Firewire (IEEE 1394) driver Interface Guide¶

Introduction and Overview¶

The Linux FireWire subsystem adds some interfaces into the Linux system to: use/maintain+any resource on IEEE 1394 bus.

The main purpose of these interfaces is to access address space on each node on IEEE 1394 bus by ISO/IEC 13213 (IEEE 1212) procedure, and to control isochronous resources on the bus by IEEE 1394 procedure.

Two types of interfaces are added, according to consumers of the interface. A set of userspace interfaces is available via firewire character devices. A set of kernel interfaces is available via exported symbols in firewire-core module.

Firewire char device data structures¶

What:           /dev/fw[0-9]+
Date:           May 2007
KernelVersion:  2.6.22
Contact:        linux1394-devel@lists.sourceforge.net
Description:
                The character device files /dev/fw* are the interface between
                firewire-core and IEEE 1394 device drivers implemented in
                userspace.  The ioctl(2)- and read(2)-based ABI is defined and
                documented in <linux/firewire-cdev.h>.

                This ABI offers most of the features which firewire-core also
                exposes to kernelspace IEEE 1394 drivers.

                Each /dev/fw* is associated with one IEEE 1394 node, which can
                be remote or local nodes.  Operations on a /dev/fw* file have
                different scope:

                  - The 1394 node which is associated with the file:

                          - Asynchronous request transmission
                          - Get the Configuration ROM
                          - Query node ID
                          - Query maximum speed of the path between this node
                            and local node

                  - The 1394 bus (i.e. "card") to which the node is attached to:

                          - Isochronous stream transmission and reception
                          - Asynchronous stream transmission and reception
                          - Asynchronous broadcast request transmission
                          - PHY packet transmission and reception
                          - Allocate, reallocate, deallocate isochronous
                            resources (channels, bandwidth) at the bus's IRM
                          - Query node IDs of local node, root node, IRM, bus
                            manager
                          - Query cycle time
                          - Bus reset initiation, bus reset event reception

                  - All 1394 buses:

                          - Allocation of IEEE 1212 address ranges on the local
                            link layers, reception of inbound requests to such
                            an address range, asynchronous response transmission
                            to inbound requests
                          - Addition of descriptors or directories to the local
                            nodes' Configuration ROM

                Due to the different scope of operations and in order to let
                userland implement different access permission models, some
                operations are restricted to /dev/fw* files that are associated
                with a local node:

                          - Addition of descriptors or directories to the local
                            nodes' Configuration ROM
                          - PHY packet transmission and reception

                A /dev/fw* file remains associated with one particular node
                during its entire life time.  Bus topology changes, and hence
                node ID changes, are tracked by firewire-core.  ABI users do not
                need to be aware of topology.

                The following file operations are supported:

                open(2)
                    Currently the only useful flags are O_RDWR.

                ioctl(2)
                    Initiate various actions.  Some take immediate effect, others
                    are performed asynchronously while or after the ioctl returns.
                    See the inline documentation in <linux/firewire-cdev.h> for
                    descriptions of all ioctls.

                poll(2), select(2), epoll_wait(2) etc.
                    Watch for events to become available to be read.

                read(2)
                    Receive various events.  There are solicited events like
                    outbound asynchronous transaction completion or isochronous
                    buffer completion, and unsolicited events such as bus resets,
                    request reception, or PHY packet reception.  Always use a read
                    buffer which is large enough to receive the largest event that
                    could ever arrive.  See <linux/firewire-cdev.h> for descriptions
                    of all event types and for which ioctls affect reception of
                    events.

                mmap(2)
                    Allocate a DMA buffer for isochronous reception or transmission
                    and map it into the process address space.  The arguments should
                    be used as follows:  addr = NULL, length = the desired buffer
                    size, i.e. number of packets times size of largest packet,
                    prot = at least PROT_READ for reception and at least PROT_WRITE
                    for transmission, flags = MAP_SHARED, fd = the handle to the
                    /dev/fw*, offset = 0.

                Isochronous reception works in packet-per-buffer fashion except
                for multichannel reception which works in buffer-fill mode.

                munmap(2)
                    Unmap the isochronous I/O buffer from the process address space.

                close(2)
                    Besides stopping and freeing I/O contexts that were associated
                    with the file descriptor, back out any changes to the local
                    nodes' Configuration ROM.  Deallocate isochronous channels and
                    bandwidth at the IRM that were marked for kernel-assisted
                    re- and deallocation.

Users:          libraw1394;
                libdc1394;
                libhinawa;
                tools like linux-firewire-utils, fwhack, ...

struct fw_cdev_event_common¶: Common part of all fw_cdev_event_* types

Definition

struct fw_cdev_event_common {
  __u64 closure;
  __u32 type;
};

Members

closure: For arbitrary use by userspace
type: Discriminates the fw_cdev_event_* types

Description

This struct may be used to access generic members of all fw_cdev_event_* types regardless of the specific type.

Data passed in the closure field for a request will be returned in the corresponding event. It is big enough to hold a pointer on all platforms. The ioctl used to set closure depends on the type of event.

struct fw_cdev_event_bus_reset¶: Sent when a bus reset occurred

Definition

struct fw_cdev_event_bus_reset {
  __u64 closure;
  __u32 type;
  __u32 node_id;
  __u32 local_node_id;
  __u32 bm_node_id;
  __u32 irm_node_id;
  __u32 root_node_id;
  __u32 generation;
};

Members

closure: See fw_cdev_event_common; set by FW_CDEV_IOC_GET_INFO ioctl
type: See fw_cdev_event_common; always FW_CDEV_EVENT_BUS_RESET
node_id: New node ID of this node
local_node_id: Node ID of the local node, i.e. of the controller
bm_node_id: Node ID of the bus manager
irm_node_id: Node ID of the iso resource manager
root_node_id: Node ID of the root node
generation: New bus generation

Description

This event is sent when the bus the device belongs to goes through a bus reset. It provides information about the new bus configuration, such as new node ID for this device, new root ID, and others.

If bm_node_id is 0xffff right after bus reset it can be reread by an FW_CDEV_IOC_GET_INFO ioctl after bus manager selection was finished. Kernels with ABI version < 4 do not set bm_node_id.

struct fw_cdev_event_response¶: Sent when a response packet was received

Definition

struct fw_cdev_event_response {
  __u64 closure;
  __u32 type;
  __u32 rcode;
  __u32 length;
  __u32 data[];
};

Members

closure: See fw_cdev_event_common; set by FW_CDEV_IOC_SEND_REQUEST or FW_CDEV_IOC_SEND_BROADCAST_REQUEST or FW_CDEV_IOC_SEND_STREAM_PACKET ioctl
type: See fw_cdev_event_common; always FW_CDEV_EVENT_RESPONSE
rcode: Response code returned by the remote node
length: Data length, i.e. the response’s payload size in bytes
data: Payload data, if any

Description

This event is sent when the stack receives a response to an outgoing request sent by FW_CDEV_IOC_SEND_REQUEST ioctl. The payload data for responses carrying data (read and lock responses) follows immediately and can be accessed through the data field.

The event is also generated after conclusions of transactions that do not involve response packets. This includes unified write transactions, broadcast write transactions, and transmission of asynchronous stream packets. rcode indicates success or failure of such transmissions.

struct fw_cdev_event_request¶: Old version of fw_cdev_event_request2

Definition

struct fw_cdev_event_request {
  __u64 closure;
  __u32 type;
  __u32 tcode;
  __u64 offset;
  __u32 handle;
  __u32 length;
  __u32 data[];
};

Members

closure: See fw_cdev_event_common; set by FW_CDEV_IOC_ALLOCATE ioctl
type: See fw_cdev_event_common; always FW_CDEV_EVENT_REQUEST
tcode: Transaction code of the incoming request
offset: The offset into the 48-bit per-node address space
handle: Reference to the kernel-side pending request
length: Data length, i.e. the request’s payload size in bytes
data: Incoming data, if any

Description

This event is sent instead of fw_cdev_event_request2 if the kernel or the client implements ABI version <= 3. fw_cdev_event_request lacks essential information; use fw_cdev_event_request2 instead.

struct fw_cdev_event_request2¶: Sent on incoming request to an address region

Definition

struct fw_cdev_event_request2 {
  __u64 closure;
  __u32 type;
  __u32 tcode;
  __u64 offset;
  __u32 source_node_id;
  __u32 destination_node_id;
  __u32 card;
  __u32 generation;
  __u32 handle;
  __u32 length;
  __u32 data[];
};

Members

closure: See fw_cdev_event_common; set by FW_CDEV_IOC_ALLOCATE ioctl
type: See fw_cdev_event_common; always FW_CDEV_EVENT_REQUEST2
tcode: Transaction code of the incoming request
offset: The offset into the 48-bit per-node address space
source_node_id: Sender node ID
destination_node_id: Destination node ID
card: The index of the card from which the request came
generation: Bus generation in which the request is valid
handle: Reference to the kernel-side pending request
length: Data length, i.e. the request’s payload size in bytes
data: Incoming data, if any

Description

This event is sent when the stack receives an incoming request to an address region registered using the FW_CDEV_IOC_ALLOCATE ioctl. The request is guaranteed to be completely contained in the specified region. Userspace is responsible for sending the response by FW_CDEV_IOC_SEND_RESPONSE ioctl, using the same handle.

The payload data for requests carrying data (write and lock requests) follows immediately and can be accessed through the data field.

Unlike fw_cdev_event_request, tcode of lock requests is one of the firewire-core specific TCODE_LOCK_MASK_SWAP…``TCODE_LOCK_VENDOR_DEPENDENT``, i.e. encodes the extended transaction code.

card may differ from fw_cdev_get_info.card because requests are received from all cards of the Linux host. source_node_id, destination_node_id, and generation pertain to that card. Destination node ID and bus generation may therefore differ from the corresponding fields of the last fw_cdev_event_bus_reset.

destination_node_id may also differ from the current node ID because of a non-local bus ID part or in case of a broadcast write request. Note, a client must call an FW_CDEV_IOC_SEND_RESPONSE ioctl even in case of a broadcast write request; the kernel will then release the kernel-side pending request but will not actually send a response packet.

In case of a write request to FCP_REQUEST or FCP_RESPONSE, the kernel already sent a write response immediately after the request was received; in this case the client must still call an FW_CDEV_IOC_SEND_RESPONSE ioctl to release the kernel-side pending request, though another response won’t be sent.

If the client subsequently needs to initiate requests to the sender node of an fw_cdev_event_request2, it needs to use a device file with matching card index, node ID, and generation for outbound requests.

struct fw_cdev_event_iso_interrupt¶: Sent when an iso packet was completed

Definition

struct fw_cdev_event_iso_interrupt {
  __u64 closure;
  __u32 type;
  __u32 cycle;
  __u32 header_length;
  __u32 header[];
};

Members

closure: See fw_cdev_event_common; set by FW_CDEV_CREATE_ISO_CONTEXT ioctl
type: See fw_cdev_event_common; always FW_CDEV_EVENT_ISO_INTERRUPT
cycle: Cycle counter of the last completed packet
header_length: Total length of following headers, in bytes
header: Stripped headers, if any

Description

This event is sent when the controller has completed an fw_cdev_iso_packet with the FW_CDEV_ISO_INTERRUPT bit set, when explicitly requested with FW_CDEV_IOC_FLUSH_ISO, or when there have been so many completed packets without the interrupt bit set that the kernel’s internal buffer for header is about to overflow. (In the last case, ABI versions < 5 drop header data up to the next interrupt packet.)

Isochronous transmit events (context type FW_CDEV_ISO_CONTEXT_TRANSMIT):

In version 3 and some implementations of version 2 of the ABI, header_length is a multiple of 4 and header contains timestamps of all packets up until the interrupt packet. The format of the timestamps is as described below for isochronous reception. In version 1 of the ABI, header_length was 0.

Isochronous receive events (context type FW_CDEV_ISO_CONTEXT_RECEIVE):

The headers stripped of all packets up until and including the interrupt packet are returned in the header field. The amount of header data per packet is as specified at iso context creation by fw_cdev_create_iso_context.header_size.

Hence, _interrupt.header_length / _context.header_size is the number of packets received in this interrupt event. The client can now iterate through the mmap()’ed DMA buffer according to this number of packets and to the buffer sizes as the client specified in fw_cdev_queue_iso.

Since version 2 of this ABI, the portion for each packet in _interrupt.header consists of the 1394 isochronous packet header, followed by a timestamp quadlet if fw_cdev_create_iso_context.header_size > 4, followed by quadlets from the packet payload if fw_cdev_create_iso_context.header_size > 8.

Format of 1394 iso packet header: 16 bits data_length, 2 bits tag, 6 bits channel, 4 bits tcode, 4 bits sy, in big endian byte order. data_length is the actual received size of the packet without the four 1394 iso packet header bytes.

Format of timestamp: 16 bits invalid, 3 bits cycleSeconds, 13 bits cycleCount, in big endian byte order.

In version 1 of the ABI, no timestamp quadlet was inserted; instead, payload data followed directly after the 1394 is header if header_size > 4. Behaviour of ver. 1 of this ABI is no longer available since ABI ver. 2.

struct fw_cdev_event_iso_interrupt_mc¶: An iso buffer chunk was completed

Definition

struct fw_cdev_event_iso_interrupt_mc {
  __u64 closure;
  __u32 type;
  __u32 completed;
};

Members

closure: See fw_cdev_event_common; set by FW_CDEV_CREATE_ISO_CONTEXT ioctl
type: FW_CDEV_EVENT_ISO_INTERRUPT_MULTICHANNEL
completed: Offset into the receive buffer; data before this offset is valid

Description

This event is sent in multichannel contexts (context type FW_CDEV_ISO_CONTEXT_RECEIVE_MULTICHANNEL) for fw_cdev_iso_packet buffer chunks that have been completely filled and that have the FW_CDEV_ISO_INTERRUPT bit set, or when explicitly requested with FW_CDEV_IOC_FLUSH_ISO.

The buffer is continuously filled with the following data, per packet:

the 1394 iso packet header as described at fw_cdev_event_iso_interrupt, but in little endian byte order,
packet payload (as many bytes as specified in the data_length field of the 1394 iso packet header) in big endian byte order,
0…3 padding bytes as needed to align the following trailer quadlet,
trailer quadlet, containing the reception timestamp as described at fw_cdev_event_iso_interrupt, but in little endian byte order.

Hence the per-packet size is data_length (rounded up to a multiple of 4) + 8. When processing the data, stop before a packet that would cross the completed offset.

A packet near the end of a buffer chunk will typically spill over into the next queued buffer chunk. It is the responsibility of the client to check for this condition, assemble a broken-up packet from its parts, and not to re-queue any buffer chunks in which as yet unread packet parts reside.

struct fw_cdev_event_iso_resource¶: Iso resources were allocated or freed

Definition

struct fw_cdev_event_iso_resource {
  __u64 closure;
  __u32 type;
  __u32 handle;
  __s32 channel;
  __s32 bandwidth;
};

Members

closure: See fw_cdev_event_common; set by``FW_CDEV_IOC_(DE)ALLOCATE_ISO_RESOURCE(_ONCE)`` ioctl
type: FW_CDEV_EVENT_ISO_RESOURCE_ALLOCATED or FW_CDEV_EVENT_ISO_RESOURCE_DEALLOCATED
handle: Reference by which an allocated resource can be deallocated
channel: Isochronous channel which was (de)allocated, if any
bandwidth: Bandwidth allocation units which were (de)allocated, if any

Description

An FW_CDEV_EVENT_ISO_RESOURCE_ALLOCATED event is sent after an isochronous resource was allocated at the IRM. The client has to check channel and bandwidth for whether the allocation actually succeeded.

An FW_CDEV_EVENT_ISO_RESOURCE_DEALLOCATED event is sent after an isochronous resource was deallocated at the IRM. It is also sent when automatic reallocation after a bus reset failed.

channel is <0 if no channel was (de)allocated or if reallocation failed. bandwidth is 0 if no bandwidth was (de)allocated or if reallocation failed.

struct fw_cdev_event_phy_packet¶: A PHY packet was transmitted or received

Definition

struct fw_cdev_event_phy_packet {
  __u64 closure;
  __u32 type;
  __u32 rcode;
  __u32 length;
  __u32 data[];
};

Members

closure: See fw_cdev_event_common; set by FW_CDEV_IOC_SEND_PHY_PACKET or FW_CDEV_IOC_RECEIVE_PHY_PACKETS ioctl
type: FW_CDEV_EVENT_PHY_PACKET_SENT or %…_RECEIVED
rcode: RCODE_…, indicates success or failure of transmission
length: Data length in bytes
data: Incoming data

Description

If type is FW_CDEV_EVENT_PHY_PACKET_SENT, length is 0 and data empty, except in case of a ping packet: Then, length is 4, and data**[0] is the ping time in 49.152MHz clocks if **rcode is RCODE_COMPLETE.

If type is FW_CDEV_EVENT_PHY_PACKET_RECEIVED, length is 8 and data consists of the two PHY packet quadlets, in host byte order.

union fw_cdev_event¶: Convenience union of fw_cdev_event_* types

Definition

union fw_cdev_event {
  struct fw_cdev_event_common             common;
  struct fw_cdev_event_bus_reset          bus_reset;
  struct fw_cdev_event_response           response;
  struct fw_cdev_event_request            request;
  struct fw_cdev_event_request2           request2;
  struct fw_cdev_event_iso_interrupt      iso_interrupt;
  struct fw_cdev_event_iso_interrupt_mc   iso_interrupt_mc;
  struct fw_cdev_event_iso_resource       iso_resource;
  struct fw_cdev_event_phy_packet         phy_packet;
};

Members

common: Valid for all types
bus_reset: Valid if common.type == FW_CDEV_EVENT_BUS_RESET
response: Valid if common.type == FW_CDEV_EVENT_RESPONSE
request: Valid if common.type == FW_CDEV_EVENT_REQUEST
request2: Valid if common.type == FW_CDEV_EVENT_REQUEST2
iso_interrupt: Valid if common.type == FW_CDEV_EVENT_ISO_INTERRUPT
iso_interrupt_mc: Valid if common.type == FW_CDEV_EVENT_ISO_INTERRUPT_MULTICHANNEL
iso_resource: Valid if common.type == FW_CDEV_EVENT_ISO_RESOURCE_ALLOCATED or FW_CDEV_EVENT_ISO_RESOURCE_DEALLOCATED
phy_packet: Valid if common.type == FW_CDEV_EVENT_PHY_PACKET_SENT or FW_CDEV_EVENT_PHY_PACKET_RECEIVED

Description

Convenience union for userspace use. Events could be read(2) into an appropriately aligned char buffer and then cast to this union for further processing. Note that for a request, response or iso_interrupt event, the data[] or header[] may make the size of the full event larger than sizeof(union fw_cdev_event). Also note that if you attempt to read(2) an event into a buffer that is not large enough for it, the data that does not fit will be discarded so that the next read(2) will return a new event.

struct fw_cdev_get_info¶: General purpose information ioctl

Definition

struct fw_cdev_get_info {
  __u32 version;
  __u32 rom_length;
  __u64 rom;
  __u64 bus_reset;
  __u64 bus_reset_closure;
  __u32 card;
};

Members

version: The version field is just a running serial number. Both an input parameter (ABI version implemented by the client) and output parameter (ABI version implemented by the kernel). A client shall fill in the ABI version for which the client was implemented. This is necessary for forward compatibility.
rom_length: If rom is non-zero, up to rom_length bytes of Configuration ROM will be copied into that user space address. In either case, rom_length is updated with the actual length of the Configuration ROM.
rom: If non-zero, address of a buffer to be filled by a copy of the device’s Configuration ROM
bus_reset: If non-zero, address of a buffer to be filled by a struct fw_cdev_event_bus_reset with the current state of the bus. This does not cause a bus reset to happen.
bus_reset_closure: Value of closure in this and subsequent bus reset events
card: The index of the card this device belongs to

Description

The FW_CDEV_IOC_GET_INFO ioctl is usually the very first one which a client performs right after it opened a /dev/fw* file.

As a side effect, reception of FW_CDEV_EVENT_BUS_RESET events to be read(2) is started by this ioctl.

struct fw_cdev_send_request¶: Send an asynchronous request packet

Definition

struct fw_cdev_send_request {
  __u32 tcode;
  __u32 length;
  __u64 offset;
  __u64 closure;
  __u64 data;
  __u32 generation;
};

Members

tcode: Transaction code of the request
length: Length of outgoing payload, in bytes
offset: 48-bit offset at destination node
closure: Passed back to userspace in the response event
data: Userspace pointer to payload
generation: The bus generation where packet is valid

Description

Send a request to the device. This ioctl implements all outgoing requests. Both quadlet and block request specify the payload as a pointer to the data in the data field. Once the transaction completes, the kernel writes an fw_cdev_event_response event back. The closure field is passed back to user space in the response event.

struct fw_cdev_send_response¶: Send an asynchronous response packet

Definition

struct fw_cdev_send_response {
  __u32 rcode;
  __u32 length;
  __u64 data;
  __u32 handle;
};

Members

rcode: Response code as determined by the userspace handler
length: Length of outgoing payload, in bytes
data: Userspace pointer to payload
handle: The handle from the fw_cdev_event_request

Description

Send a response to an incoming request. By setting up an address range using the FW_CDEV_IOC_ALLOCATE ioctl, userspace can listen for incoming requests. An incoming request will generate an FW_CDEV_EVENT_REQUEST, and userspace must send a reply using this ioctl. The event has a handle to the kernel-side pending transaction, which should be used with this ioctl.

struct fw_cdev_allocate¶: Allocate a CSR in an address range

Definition

struct fw_cdev_allocate {
  __u64 offset;
  __u64 closure;
  __u32 length;
  __u32 handle;
  __u64 region_end;
};

Members

offset: Start offset of the address range
closure: To be passed back to userspace in request events
length: Length of the CSR, in bytes
handle: Handle to the allocation, written by the kernel
region_end: First address above the address range (added in ABI v4, 2.6.36)

Description

Allocate an address range in the 48-bit address space on the local node (the controller). This allows userspace to listen for requests with an offset within that address range. Every time when the kernel receives a request within the range, an fw_cdev_event_request2 event will be emitted. (If the kernel or the client implements ABI version <= 3, an fw_cdev_event_request will be generated instead.)

The closure field is passed back to userspace in these request events. The handle field is an out parameter, returning a handle to the allocated range to be used for later deallocation of the range.

The address range is allocated on all local nodes. The address allocation is exclusive except for the FCP command and response registers. If an exclusive address region is already in use, the ioctl fails with errno set to EBUSY.

If kernel and client implement ABI version >= 4, the kernel looks up a free spot of size length inside [offset..**region_end**) and, if found, writes the start address of the new CSR back in offset. I.e. offset is an in and out parameter. If this automatic placement of a CSR in a bigger address range is not desired, the client simply needs to set region_end = offset + length.

If the kernel or the client implements ABI version <= 3, region_end is ignored and effectively assumed to be offset + length.

region_end is only present in a kernel header >= 2.6.36. If necessary, this can for example be tested by #ifdef FW_CDEV_EVENT_REQUEST2.

struct fw_cdev_deallocate¶: Free a CSR address range or isochronous resource

Definition

struct fw_cdev_deallocate {
  __u32 handle;
};

Members

handle: Handle to the address range or iso resource, as returned by the kernel when the range or resource was allocated

struct fw_cdev_initiate_bus_reset¶: Initiate a bus reset

Definition

struct fw_cdev_initiate_bus_reset {
  __u32 type;
};

Members

type: FW_CDEV_SHORT_RESET or FW_CDEV_LONG_RESET

Description

Initiate a bus reset for the bus this device is on. The bus reset can be either the original (long) bus reset or the arbitrated (short) bus reset introduced in 1394a-2000.

The ioctl returns immediately. A subsequent fw_cdev_event_bus_reset indicates when the reset actually happened. Since ABI v4, this may be considerably later than the ioctl because the kernel ensures a grace period between subsequent bus resets as per IEEE 1394 bus management specification.

struct fw_cdev_add_descriptor¶: Add contents to the local node’s config ROM

Definition

struct fw_cdev_add_descriptor {
  __u32 immediate;
  __u32 key;
  __u64 data;
  __u32 length;
  __u32 handle;
};

Members

immediate: If non-zero, immediate key to insert before pointer
key: Upper 8 bits of root directory pointer
data: Userspace pointer to contents of descriptor block
length: Length of descriptor block data, in quadlets
handle: Handle to the descriptor, written by the kernel

Description

Add a descriptor block and optionally a preceding immediate key to the local node’s Configuration ROM.

The key field specifies the upper 8 bits of the descriptor root directory pointer and the data and length fields specify the contents. The key should be of the form 0xXX000000. The offset part of the root directory entry will be filled in by the kernel.

If not 0, the immediate field specifies an immediate key which will be inserted before the root directory pointer.

immediate, key, and data array elements are CPU-endian quadlets.

If successful, the kernel adds the descriptor and writes back a handle to the kernel-side object to be used for later removal of the descriptor block and immediate key. The kernel will also generate a bus reset to signal the change of the Configuration ROM to other nodes.

This ioctl affects the Configuration ROMs of all local nodes. The ioctl only succeeds on device files which represent a local node.

struct fw_cdev_remove_descriptor¶: Remove contents from the Configuration ROM

Definition

struct fw_cdev_remove_descriptor {
  __u32 handle;
};

Members

handle: Handle to the descriptor, as returned by the kernel when the descriptor was added

Description

Remove a descriptor block and accompanying immediate key from the local nodes’ Configuration ROMs. The kernel will also generate a bus reset to signal the change of the Configuration ROM to other nodes.

struct fw_cdev_create_iso_context¶: Create a context for isochronous I/O

Definition

struct fw_cdev_create_iso_context {
  __u32 type;
  __u32 header_size;
  __u32 channel;
  __u32 speed;
  __u64 closure;
  __u32 handle;
};

Members

type: FW_CDEV_ISO_CONTEXT_TRANSMIT or FW_CDEV_ISO_CONTEXT_RECEIVE or FW_CDEV_ISO_CONTEXT_RECEIVE_MULTICHANNEL
header_size: Header size to strip in single-channel reception
channel: Channel to bind to in single-channel reception or transmission
speed: Transmission speed
closure: To be returned in fw_cdev_event_iso_interrupt or fw_cdev_event_iso_interrupt_multichannel
handle: Handle to context, written back by kernel

Description

Prior to sending or receiving isochronous I/O, a context must be created. The context records information about the transmit or receive configuration and typically maps to an underlying hardware resource. A context is set up for either sending or receiving. It is bound to a specific isochronous channel.

In case of multichannel reception, header_size and channel are ignored and the channels are selected by FW_CDEV_IOC_SET_ISO_CHANNELS.

For FW_CDEV_ISO_CONTEXT_RECEIVE contexts, header_size must be at least 4 and must be a multiple of 4. It is ignored in other context types.

speed is ignored in receive context types.

If a context was successfully created, the kernel writes back a handle to the context, which must be passed in for subsequent operations on that context.

Limitations: No more than one iso context can be created per fd. The total number of contexts that all userspace and kernelspace drivers can create on a card at a time is a hardware limit, typically 4 or 8 contexts per direction, and of them at most one multichannel receive context.

struct fw_cdev_set_iso_channels¶: Select channels in multichannel reception

Definition

struct fw_cdev_set_iso_channels {
  __u64 channels;
  __u32 handle;
};

Members

channels: Bitmask of channels to listen to
handle: Handle of the mutichannel receive context

Description

channels is the bitwise or of 1ULL << n for each channel n to listen to.

The ioctl fails with errno EBUSY if there is already another receive context on a channel in channels. In that case, the bitmask of all unoccupied channels is returned in channels.

struct fw_cdev_iso_packet¶: Isochronous packet

Definition

struct fw_cdev_iso_packet {
  __u32 control;
  __u32 header[];
};

Members

control: Contains the header length (8 uppermost bits), the sy field (4 bits), the tag field (2 bits), a sync flag or a skip flag (1 bit), an interrupt flag (1 bit), and the payload length (16 lowermost bits)
header: Header and payload in case of a transmit context.

Description

struct fw_cdev_iso_packet is used to describe isochronous packet queues. Use the FW_CDEV_ISO_* macros to fill in control. The header array is empty in case of receive contexts.

Context type FW_CDEV_ISO_CONTEXT_TRANSMIT:

control.HEADER_LENGTH must be a multiple of 4. It specifies the numbers of bytes in header that will be prepended to the packet’s payload. These bytes are copied into the kernel and will not be accessed after the ioctl has returned.

The control.SY and TAG fields are copied to the iso packet header. These fields are specified by IEEE 1394a and IEC 61883-1.

The control.SKIP flag specifies that no packet is to be sent in a frame. When using this, all other fields except control.INTERRUPT must be zero.

When a packet with the control.INTERRUPT flag set has been completed, an fw_cdev_event_iso_interrupt event will be sent.

Context type FW_CDEV_ISO_CONTEXT_RECEIVE:

control.HEADER_LENGTH must be a multiple of the context’s header_size. If the HEADER_LENGTH is larger than the context’s header_size, multiple packets are queued for this entry.

The control.SY and TAG fields are ignored.

If the control.SYNC flag is set, the context drops all packets until a packet with a sy field is received which matches fw_cdev_start_iso.sync.

control.PAYLOAD_LENGTH defines how many payload bytes can be received for one packet (in addition to payload quadlets that have been defined as headers and are stripped and returned in the fw_cdev_event_iso_interrupt structure). If more bytes are received, the additional bytes are dropped. If less bytes are received, the remaining bytes in this part of the payload buffer will not be written to, not even by the next packet. I.e., packets received in consecutive frames will not necessarily be consecutive in memory. If an entry has queued multiple packets, the PAYLOAD_LENGTH is divided equally among them.

When a packet with the control.INTERRUPT flag set has been completed, an fw_cdev_event_iso_interrupt event will be sent. An entry that has queued multiple receive packets is completed when its last packet is completed.

Context type FW_CDEV_ISO_CONTEXT_RECEIVE_MULTICHANNEL:

Here, fw_cdev_iso_packet would be more aptly named _iso_buffer_chunk since it specifies a chunk of the mmap()’ed buffer, while the number and alignment of packets to be placed into the buffer chunk is not known beforehand.

control.PAYLOAD_LENGTH is the size of the buffer chunk and specifies room for header, payload, padding, and trailer bytes of one or more packets. It must be a multiple of 4.

control.HEADER_LENGTH, TAG and SY are ignored. SYNC is treated as described for single-channel reception.

When a buffer chunk with the control.INTERRUPT flag set has been filled entirely, an fw_cdev_event_iso_interrupt_mc event will be sent.

struct fw_cdev_queue_iso¶: Queue isochronous packets for I/O

Definition

struct fw_cdev_queue_iso {
  __u64 packets;
  __u64 data;
  __u32 size;
  __u32 handle;
};

Members

packets: Userspace pointer to an array of fw_cdev_iso_packet
data: Pointer into mmap()’ed payload buffer
size: Size of the packets array, in bytes
handle: Isochronous context handle

Description

Queue a number of isochronous packets for reception or transmission. This ioctl takes a pointer to an array of fw_cdev_iso_packet structs, which describe how to transmit from or receive into a contiguous region of a mmap()’ed payload buffer. As part of transmit packet descriptors, a series of headers can be supplied, which will be prepended to the payload during DMA.

The kernel may or may not queue all packets, but will write back updated values of the packets, data and size fields, so the ioctl can be resubmitted easily.

In case of a multichannel receive context, data must be quadlet-aligned relative to the buffer start.

struct fw_cdev_start_iso¶: Start an isochronous transmission or reception

Definition

struct fw_cdev_start_iso {
  __s32 cycle;
  __u32 sync;
  __u32 tags;
  __u32 handle;
};

Members

cycle: Cycle in which to start I/O. If cycle is greater than or equal to 0, the I/O will start on that cycle.
sync: Determines the value to wait for receive packets that have the FW_CDEV_ISO_SYNC bit set
tags: Tag filter bit mask. Only valid for isochronous reception. Determines the tag values for which packets will be accepted. Use FW_CDEV_ISO_CONTEXT_MATCH_* macros to set tags.
handle: Isochronous context handle within which to transmit or receive

struct fw_cdev_stop_iso¶: Stop an isochronous transmission or reception

Definition

struct fw_cdev_stop_iso {
  __u32 handle;
};

Members

handle: Handle of isochronous context to stop

struct fw_cdev_flush_iso¶: flush completed iso packets

Definition

struct fw_cdev_flush_iso {
  __u32 handle;
};

Members

handle: handle of isochronous context to flush

Description

For FW_CDEV_ISO_CONTEXT_TRANSMIT or FW_CDEV_ISO_CONTEXT_RECEIVE contexts, report any completed packets.

For FW_CDEV_ISO_CONTEXT_RECEIVE_MULTICHANNEL contexts, report the current offset in the receive buffer, if it has changed; this is typically in the middle of some buffer chunk.

Any FW_CDEV_EVENT_ISO_INTERRUPT or FW_CDEV_EVENT_ISO_INTERRUPT_MULTICHANNEL events generated by this ioctl are sent synchronously, i.e., are available for reading from the file descriptor when this ioctl returns.

struct fw_cdev_get_cycle_timer¶: read cycle timer register

Definition

struct fw_cdev_get_cycle_timer {
  __u64 local_time;
  __u32 cycle_timer;
};

Members

local_time: system time, in microseconds since the Epoch
cycle_timer: Cycle Time register contents

Description

Same as FW_CDEV_IOC_GET_CYCLE_TIMER2, but fixed to use CLOCK_REALTIME and only with microseconds resolution.

In version 1 and 2 of the ABI, this ioctl returned unreliable (non- monotonic) cycle_timer values on certain controllers.

struct fw_cdev_get_cycle_timer2¶: read cycle timer register

Definition

struct fw_cdev_get_cycle_timer2 {
  __s64 tv_sec;
  __s32 tv_nsec;
  __s32 clk_id;
  __u32 cycle_timer;
};

Members

tv_sec: system time, seconds
tv_nsec: system time, sub-seconds part in nanoseconds
clk_id: input parameter, clock from which to get the system time
cycle_timer: Cycle Time register contents

Description

The FW_CDEV_IOC_GET_CYCLE_TIMER2 ioctl reads the isochronous cycle timer and also the system clock. This allows to correlate reception time of isochronous packets with system time.

clk_id lets you choose a clock like with POSIX’ clock_gettime function. Supported clk_id values are POSIX’ CLOCK_REALTIME and CLOCK_MONOTONIC and Linux’ CLOCK_MONOTONIC_RAW.

cycle_timer consists of 7 bits cycleSeconds, 13 bits cycleCount, and 12 bits cycleOffset, in host byte order. Cf. the Cycle Time register per IEEE 1394 or Isochronous Cycle Timer register per OHCI-1394.

struct fw_cdev_allocate_iso_resource¶: (De)allocate a channel or bandwidth

Definition

struct fw_cdev_allocate_iso_resource {
  __u64 closure;
  __u64 channels;
  __u32 bandwidth;
  __u32 handle;
};

Members

closure: Passed back to userspace in corresponding iso resource events
channels: Isochronous channels of which one is to be (de)allocated
bandwidth: Isochronous bandwidth units to be (de)allocated
handle: Handle to the allocation, written by the kernel (only valid in case of FW_CDEV_IOC_ALLOCATE_ISO_RESOURCE ioctls)

Description

The FW_CDEV_IOC_ALLOCATE_ISO_RESOURCE ioctl initiates allocation of an isochronous channel and/or of isochronous bandwidth at the isochronous resource manager (IRM). Only one of the channels specified in channels is allocated. An FW_CDEV_EVENT_ISO_RESOURCE_ALLOCATED is sent after communication with the IRM, indicating success or failure in the event data. The kernel will automatically reallocate the resources after bus resets. Should a reallocation fail, an FW_CDEV_EVENT_ISO_RESOURCE_DEALLOCATED event will be sent. The kernel will also automatically deallocate the resources when the file descriptor is closed.

The FW_CDEV_IOC_DEALLOCATE_ISO_RESOURCE ioctl can be used to initiate deallocation of resources which were allocated as described above. An FW_CDEV_EVENT_ISO_RESOURCE_DEALLOCATED event concludes this operation.

The FW_CDEV_IOC_ALLOCATE_ISO_RESOURCE_ONCE ioctl is a variant of allocation without automatic re- or deallocation. An FW_CDEV_EVENT_ISO_RESOURCE_ALLOCATED event concludes this operation, indicating success or failure in its data.

The FW_CDEV_IOC_DEALLOCATE_ISO_RESOURCE_ONCE ioctl works like FW_CDEV_IOC_ALLOCATE_ISO_RESOURCE_ONCE except that resources are freed instead of allocated. An FW_CDEV_EVENT_ISO_RESOURCE_DEALLOCATED event concludes this operation.

To summarize, FW_CDEV_IOC_ALLOCATE_ISO_RESOURCE allocates iso resources for the lifetime of the fd or handle. In contrast, FW_CDEV_IOC_ALLOCATE_ISO_RESOURCE_ONCE allocates iso resources for the duration of a bus generation.

channels is a host-endian bitfield with the least significant bit representing channel 0 and the most significant bit representing channel 63: 1ULL << c for each channel c that is a candidate for (de)allocation.

bandwidth is expressed in bandwidth allocation units, i.e. the time to send one quadlet of data (payload or header data) at speed S1600.

struct fw_cdev_send_stream_packet¶: send an asynchronous stream packet

Definition

struct fw_cdev_send_stream_packet {
  __u32 length;
  __u32 tag;
  __u32 channel;
  __u32 sy;
  __u64 closure;
  __u64 data;
  __u32 generation;
  __u32 speed;
};

Members

length: Length of outgoing payload, in bytes
tag: Data format tag
channel: Isochronous channel to transmit to
sy: Synchronization code
closure: Passed back to userspace in the response event
data: Userspace pointer to payload
generation: The bus generation where packet is valid
speed: Speed to transmit at

Description

The FW_CDEV_IOC_SEND_STREAM_PACKET ioctl sends an asynchronous stream packet to every device which is listening to the specified channel. The kernel writes an fw_cdev_event_response event which indicates success or failure of the transmission.

struct fw_cdev_send_phy_packet¶: send a PHY packet

Definition

struct fw_cdev_send_phy_packet {
  __u64 closure;
  __u32 data[2];
  __u32 generation;
};

Members

closure: Passed back to userspace in the PHY-packet-sent event
data: First and second quadlet of the PHY packet
generation: The bus generation where packet is valid

Description

The FW_CDEV_IOC_SEND_PHY_PACKET ioctl sends a PHY packet to all nodes on the same card as this device. After transmission, an FW_CDEV_EVENT_PHY_PACKET_SENT event is generated.

The payload data[] shall be specified in host byte order. Usually, data[1] needs to be the bitwise inverse of data[0]. VersaPHY packets are an exception to this rule.

The ioctl is only permitted on device files which represent a local node.

struct fw_cdev_receive_phy_packets¶: start reception of PHY packets

Definition

struct fw_cdev_receive_phy_packets {
  __u64 closure;
};

Members

closure: Passed back to userspace in phy packet events

Description

This ioctl activates issuing of FW_CDEV_EVENT_PHY_PACKET_RECEIVED due to incoming PHY packets from any node on the same bus as the device.

The ioctl is only permitted on device files which represent a local node.

Firewire device probing and sysfs interfaces¶

What:           /sys/bus/firewire/devices/fw[0-9]+/
Date:           May 2007
KernelVersion:  2.6.22
Contact:        linux1394-devel@lists.sourceforge.net
Description:
                IEEE 1394 node device attributes.
                Read-only.  Mutable during the node device's lifetime.
                See IEEE 1212 for semantic definitions.

                config_rom
                        Contents of the Configuration ROM register.
                        Binary attribute; an array of host-endian u32.

                guid
                        The node's EUI-64 in the bus information block of
                        Configuration ROM.
                        Hexadecimal string representation of an u64.


What:           /sys/bus/firewire/devices/fw[0-9]+/units
Date:           June 2009
KernelVersion:  2.6.31
Contact:        linux1394-devel@lists.sourceforge.net
Description:
                IEEE 1394 node device attribute.
                Read-only.  Mutable during the node device's lifetime.
                See IEEE 1212 for semantic definitions.

                units
                        Summary of all units present in an IEEE 1394 node.
                        Contains space-separated tuples of specifier_id and
                        version of each unit present in the node.  Specifier_id
                        and version are hexadecimal string representations of
                        u24 of the respective unit directory entries.
                        Specifier_id and version within each tuple are separated
                        by a colon.

Users:          udev rules to set ownership and access permissions or ACLs of
                /dev/fw[0-9]+ character device files


What:           /sys/bus/firewire/devices/fw[0-9]+/is_local
Date:           July 2012
KernelVersion:  3.6
Contact:        linux1394-devel@lists.sourceforge.net
Description:
                IEEE 1394 node device attribute.
                Read-only and immutable.
Values:         1: The sysfs entry represents a local node (a controller card).

                0: The sysfs entry represents a remote node.


What:           /sys/bus/firewire/devices/fw[0-9]+[.][0-9]+/
Date:           May 2007
KernelVersion:  2.6.22
Contact:        linux1394-devel@lists.sourceforge.net
Description:
                IEEE 1394 unit device attributes.
                Read-only.  Immutable during the unit device's lifetime.
                See IEEE 1212 for semantic definitions.

                modalias
                        Same as MODALIAS in the uevent at device creation.

                rom_index
                        Offset of the unit directory within the parent device's
                        (node device's) Configuration ROM, in quadlets.
                        Decimal string representation.


What:           /sys/bus/firewire/devices/*/
Date:           May 2007
KernelVersion:  2.6.22
Contact:        linux1394-devel@lists.sourceforge.net
Description:
                Attributes common to IEEE 1394 node devices and unit devices.
                Read-only.  Mutable during the node device's lifetime.
                Immutable during the unit device's lifetime.
                See IEEE 1212 for semantic definitions.

                These attributes are only created if the root directory of an
                IEEE 1394 node or the unit directory of an IEEE 1394 unit
                actually contains according entries.

                hardware_version
                        Hexadecimal string representation of an u24.

                hardware_version_name
                        Contents of a respective textual descriptor leaf.

                model
                        Hexadecimal string representation of an u24.

                model_name
                        Contents of a respective textual descriptor leaf.

                specifier_id
                        Hexadecimal string representation of an u24.
                        Mandatory in unit directories according to IEEE 1212.

                vendor
                        Hexadecimal string representation of an u24.
                        Mandatory in the root directory according to IEEE 1212.

                vendor_name
                        Contents of a respective textual descriptor leaf.

                version
                        Hexadecimal string representation of an u24.
                        Mandatory in unit directories according to IEEE 1212.


What:           /sys/bus/firewire/drivers/sbp2/fw*/host*/target*/*:*:*:*/ieee1394_id
                formerly
                /sys/bus/ieee1394/drivers/sbp2/fw*/host*/target*/*:*:*:*/ieee1394_id
Date:           Feb 2004
KernelVersion:  2.6.4
Contact:        linux1394-devel@lists.sourceforge.net
Description:
                SCSI target port identifier and logical unit identifier of a
                logical unit of an SBP-2 target.  The identifiers are specified
                in SAM-2...SAM-4 annex A.  They are persistent and world-wide
                unique properties the SBP-2 attached target.

                Read-only attribute, immutable during the target's lifetime.
                Format, as exposed by firewire-sbp2 since 2.6.22, May 2007:
                Colon-separated hexadecimal string representations of

                        u64 EUI-64 : u24 directory_ID : u16 LUN

                without 0x prefixes, without whitespace.  The former sbp2 driver
                (removed in 2.6.37 after being superseded by firewire-sbp2) used
                a somewhat shorter format which was not as close to SAM.

Users:          udev rules to create /dev/disk/by-id/ symlinks

int fw_csr_string(const u32 *directory, int key, char *buf, size_t size)¶: reads a string from the configuration ROM

Parameters

const u32 *directory: e.g. root directory or unit directory
int key: the key of the preceding directory entry
char *buf: where to put the string
size_t size: size of buf, in bytes

Description

The string is taken from a minimal ASCII text descriptor leaf just after the entry with the key. The string is zero-terminated. An overlong string is silently truncated such that it and the zero byte fit into size.

Returns strlen(buf) or a negative error code.

Firewire core transaction interfaces¶

void fw_send_request(struct fw_card *card, struct fw_transaction *t, int tcode, int destination_id, int generation, int speed, unsigned long long offset, void *payload, size_t length, fw_transaction_callback_t callback, void *callback_data)¶: submit a request packet for transmission

Parameters

struct fw_card *card: interface to send the request at
struct fw_transaction *t: transaction instance to which the request belongs
int tcode: transaction code
int destination_id: destination node ID, consisting of bus_ID and phy_ID
int generation: bus generation in which request and response are valid
int speed: transmission speed
unsigned long long offset: 48bit wide offset into destination’s address space
void *payload: data payload for the request subaction
size_t length: length of the payload, in bytes
fw_transaction_callback_t callback: function to be called when the transaction is completed
void *callback_data: data to be passed to the transaction completion callback

Description

Submit a request packet into the asynchronous request transmission queue. Can be called from atomic context. If you prefer a blocking API, use fw_run_transaction() in a context that can sleep.

In case of lock requests, specify one of the firewire-core specific TCODE_ constants instead of TCODE_LOCK_REQUEST in tcode.

Make sure that the value in destination_id is not older than the one in generation. Otherwise the request is in danger to be sent to a wrong node.

In case of asynchronous stream packets i.e. TCODE_STREAM_DATA, the caller needs to synthesize destination_id with fw_stream_packet_destination_id(). It will contain tag, channel, and sy data instead of a node ID then.

The payload buffer at data is going to be DMA-mapped except in case of length <= 8 or of local (loopback) requests. Hence make sure that the buffer complies with the restrictions of the streaming DMA mapping API. payload must not be freed before the callback is called.

In case of request types without payload, data is NULL and length is 0.

After the transaction is completed successfully or unsuccessfully, the callback will be called. Among its parameters is the response code which is either one of the rcodes per IEEE 1394 or, in case of internal errors, the firewire-core specific RCODE_SEND_ERROR. The other firewire-core specific rcodes (RCODE_CANCELLED, RCODE_BUSY, RCODE_GENERATION, RCODE_NO_ACK) denote transaction timeout, busy responder, stale request generation, or missing ACK respectively.

Note some timing corner cases: fw_send_request() may complete much earlier than when the request packet actually hits the wire. On the other hand, transaction completion and hence execution of callback may happen even before fw_send_request() returns.

int fw_run_transaction(struct fw_card *card, int tcode, int destination_id, int generation, int speed, unsigned long long offset, void *payload, size_t length)¶: send request and sleep until transaction is completed

Parameters

struct fw_card *card: card interface for this request
int tcode: transaction code
int destination_id: destination node ID, consisting of bus_ID and phy_ID
int generation: bus generation in which request and response are valid
int speed: transmission speed
unsigned long long offset: 48bit wide offset into destination’s address space
void *payload: data payload for the request subaction
size_t length: length of the payload, in bytes

Description

Returns the RCODE. See fw_send_request() for parameter documentation. Unlike fw_send_request(), data points to the payload of the request or/and to the payload of the response. DMA mapping restrictions apply to outbound request payloads of >= 8 bytes but not to inbound response payloads.

int fw_core_add_address_handler(struct fw_address_handler *handler, const struct fw_address_region *region)¶: register for incoming requests

Parameters

struct fw_address_handler *handler: callback
const struct fw_address_region *region: region in the IEEE 1212 node space address range

Description

region->start, ->end, and handler->length have to be quadlet-aligned.

When a request is received that falls within the specified address range, the specified callback is invoked. The parameters passed to the callback give the details of the particular request.

To be called in process context. Return value: 0 on success, non-zero otherwise.

The start offset of the handler’s address region is determined by fw_core_add_address_handler() and is returned in handler->offset.

Address allocations are exclusive, except for the FCP registers.

void fw_core_remove_address_handler(struct fw_address_handler *handler)¶: unregister an address handler

Parameters

struct fw_address_handler *handler: callback

Description

To be called in process context.

When fw_core_remove_address_handler() returns, handler->callback() is guaranteed to not run on any CPU anymore.

int fw_get_request_speed(struct fw_request *request)¶: returns speed at which the request was received

Parameters

struct fw_request *request: firewire request data

u32 fw_request_get_timestamp(const struct fw_request *request)¶: Get timestamp of the request.

Parameters

const struct fw_request *request: The opaque pointer to request structure.

Description

Get timestamp when 1394 OHCI controller receives the asynchronous request subaction. The timestamp consists of the low order 3 bits of second field and the full 13 bits of count field of isochronous cycle time register.

Return

timestamp of the request.

const char *fw_rcode_string(int rcode)¶: convert a firewire result code to an error description

Parameters

int rcode: the result code

Firewire Isochronous I/O interfaces¶

void fw_iso_resource_manage(struct fw_card *card, int generation, u64 channels_mask, int *channel, int *bandwidth, bool allocate)¶: Allocate or deallocate a channel and/or bandwidth

Parameters

struct fw_card *card: card interface for this action
int generation: bus generation
u64 channels_mask: bitmask for channel allocation
int *channel: pointer for returning channel allocation result
int *bandwidth: pointer for returning bandwidth allocation result
bool allocate: whether to allocate (true) or deallocate (false)

Description

In parameters: card, generation, channels_mask, bandwidth, allocate Out parameters: channel, bandwidth

This function blocks (sleeps) during communication with the IRM.

Allocates or deallocates at most one channel out of channels_mask. channels_mask is a bitfield with MSB for channel 63 and LSB for channel 0. (Note, the IRM’s CHANNELS_AVAILABLE is a big-endian bitfield with MSB for channel 0 and LSB for channel 63.) Allocates or deallocates as many bandwidth allocation units as specified.

Returns channel < 0 if no channel was allocated or deallocated. Returns bandwidth = 0 if no bandwidth was allocated or deallocated.

If generation is stale, deallocations succeed but allocations fail with channel = -EAGAIN.

If channel allocation fails, no bandwidth will be allocated either. If bandwidth allocation fails, no channel will be allocated either. But deallocations of channel and bandwidth are tried independently of each other’s success.