| NAME | DESCRIPTION | EXAMPLE | SEE ALSO | COLOPHON | The Linux Programming Interface |
SPUFS(7) Linux Programmer's Manual SPUFS(7)
spufs - SPU file system
The SPU file system is used on PowerPC machines that implement the Cell
Broadband Engine Architecture in order to access Synergistic Processor Units
(SPUs).
The file system provides a name space similar to POSIX shared memory or
message queues. Users that have write permissions on the file system can use
spu_create(2) to establish SPU contexts under the spufs root directory.
Every SPU context is represented by a directory containing a predefined set of
files. These files can be used for manipulating the state of the logical SPU.
Users can change permissions on the files, but can't add or remove files.
uid=<uid>
Set the user owning the mount point; the default is 0 (root).
gid=<gid>
Set the group owning the mount point; the default is 0 (root).
mode=<mode>
Set the mode of the top-level directory in spufs, as an octal mode
string. The default is 0775.
The files in spufs mostly follow the standard behavior for regular system
calls like read(2) or write(2), but often support only a subset of the
operations supported on regular file systems. This list details the supported
operations and the deviations from the standard behavior described in the
respective man pages.
All files that support the read(2) operation also support readv(2) and all
files that support the write(2) operation also support writev(2). All files
support the access(2) and stat(2) family of operations, but for the latter
call, the only fields of the returned stat structure that contain reliable
information are st_mode, st_nlink, st_uid, and st_gid.
All files support the chmod(2)/fchmod(2) and chown(2)/fchown(2) operations,
but will not be able to grant permissions that contradict the possible
operations (e.g., read access on the wbox file).
The current set of files is:
/capabilities
Contains a comma-delimited string representing the capabilities of this
SPU context. Possible capabilities are:
sched This context may be scheduled.
step This context can be run in single-step mode, for debugging.
New capabilities flags may be added in the future.
/mem the contents of the local storage memory of the SPU. This can be
accessed like a regular shared memory file and contains both code and
data in the address space of the SPU. The possible operations on an
open mem file are:
read(2), pread(2), write(2), pwrite(2), lseek(2)
These operate as usual, with the exception that lseek(2),
write(2), and pwrite(2) are not supported beyond the end of the
file. The file size is the size of the local storage of the
SPU, which is normally 256 kilobytes.
mmap(2)
Mapping mem into the process address space provides access to
the SPU local storage within the process address space. Only
MAP_SHARED mappings are allowed.
/regs Contains the saved general-purpose registers of the SPU context. This
file contains the 128-bit values of each register, from register 0 to
register 127, in order. This allows the general-purpose registers to
be inspected for debugging.
Reading to or writing from this file requires that the context is
scheduled out, so use of this file is not recommended in normal program
operation.
The regs file is not present on contexts that have been created with
the SPU_CREATE_NOSCHED flag.
/mbox The first SPU-to-CPU communication mailbox. This file is read-only and
can be read in units of 4 bytes. The file can only be used in
nonblocking mode - even poll(2) cannot be used to block on this file.
The only possible operation on an open mbox file is:
read(2)
If count is smaller than four, read(2) returns -1 and sets errno
to EINVAL. If there is no data available in the mailbox (i.e.,
the SPU has not sent a mailbox message), the return value is set
to -1 and errno is set to EAGAIN. When data has been read
successfully, four bytes are placed in the data buffer and the
value four is returned.
/ibox The second SPU-to-CPU communication mailbox. This file is similar to
the first mailbox file, but can be read in blocking I/O mode, thus
calling read(2) on an open ibox file will block until the SPU has
written data to its interrupt mailbox channel (unless the file has been
opened with O_NONBLOCK, see below). Also, poll(2) and similar system
calls can be used to monitor for the presence of mailbox data.
The possible operations on an open ibox file are:
read(2)
If count is smaller than four, read(2) returns -1 and sets errno
to EINVAL. If there is no data available in the mailbox and the
file descriptor has been opened with O_NONBLOCK, the return
value is set to -1 and errno is set to EAGAIN.
If there is no data available in the mailbox and the file
descriptor has been opened without O_NONBLOCK, the call will
block until the SPU writes to its interrupt mailbox channel.
When data has been read successfully, four bytes are placed in
the data buffer and the value four is returned.
poll(2)
Poll on the ibox file returns (POLLIN | POLLRDNORM) whenever
data is available for reading.
/wbox The CPU-to-SPU communication mailbox. It is write-only and can be
written in units of four bytes. If the mailbox is full, write(2) will
block, and poll(2) can be used to block until the mailbox is available
for writing again. The possible operations on an open wbox file are:
write(2)
If count is smaller than four, write(2) returns -1 and sets
errno to EINVAL. If there is no space available in the mailbox
and the file descriptor has been opened with O_NONBLOCK, the
return value is set to -1 and errno is set to EAGAIN.
If there is no space available in the mailbox and the file
descriptor has been opened without O_NONBLOCK, the call will
block until the SPU reads from its PPE (PowerPC Processing
Element) mailbox channel. When data has been written
successfully, the system call returns four as its function
result.
poll(2)
A poll on the wbox file returns (POLLOUT | POLLWRNORM) whenever
space is available for writing.
/mbox_stat, /ibox_stat, /wbox_stat
These are read-only files that contain the length of the current queue
of each mailbox, i.e., how many words can be read from mbox or ibox or
how many words can be written to wbox without blocking. The files can
be read only in four-byte units and return a big-endian binary integer
number. The only possible operation on an open *box_stat file is:
read(2)
If count is smaller than four, read(2) returns -1 and sets errno
to EINVAL. Otherwise, a four-byte value is placed in the data
buffer. This value is the number of elements that can be read
from (for mbox_stat and ibox_stat) or written to (for wbox_stat)
the respective mailbox without blocking or returning an EAGAIN
error.
/npc, /decr, /decr_status, /spu_tag_mask, /event_mask, /event_status, /srr0,
/lslr
Internal registers of the SPU. These files contain an ASCII string
representing the hex value of the specified register. Reads and writes
on these files (except for npc, see below) require that the SPU context
be scheduled out, so frequent access to these files is not recommended
for normal program operation.
The contents of these files are:
npc Next Program Counter - only valid when the SPU is in a
stopped state.
decr SPU Decrementer
decr_status Decrementer Status
spu_tag_mask MFC tag mask for SPU DMA
event_mask Event mask for SPU interrupts
event_status Number of SPU events pending (read-only)
srr0 Interrupt Return address register
lslr Local Store Limit Register
The possible operations on these files are:
read(2)
Reads the current register value. If the register value is
larger than the buffer passed to the read(2) system call,
subsequent reads will continue reading from the same buffer,
until the end of the buffer is reached.
When a complete string has been read, all subsequent read
operations will return zero bytes and a new file descriptor
needs to be opened to read a new value.
write(2)
A write(2) operation on the file sets the register to the value
given in the string. The string is parsed from the beginning
until the first nonnumeric character or the end of the buffer.
Subsequent writes to the same file descriptor overwrite the
previous setting.
Except for the npc file, these files are not present on contexts
that have been created with the SPU_CREATE_NOSCHED flag.
/fpcr This file provides access to the Floating Point Status and Control
Register (fcpr) as a binary, four-byte file. The operations on the
fpcr file are:
read(2)
If count is smaller than four, read(2) returns -1 and sets errno
to EINVAL. Otherwise, a four-byte value is placed in the data
buffer; this is the current value of the fpcr register.
write(2)
If count is smaller than four, write(2) returns -1 and sets
errno to EINVAL. Otherwise, a four-byte value is copied from
the data buffer, updating the value of the fpcr register.
/signal1, /signal2
The files provide access to the two signal notification channels of an
SPU. These are read-write files that operate on four-byte words.
Writing to one of these files triggers an interrupt on the SPU. The
value written to the signal files can be read from the SPU through a
channel read or from host user space through the file. After the value
has been read by the SPU, it is reset to zero. The possible operations
on an open signal1 or signal2 file are:
read(2)
If count is smaller than four, read(2) returns -1 and sets errno
to EINVAL. Otherwise, a four-byte value is placed in the data
buffer; this is the current value of the specified signal
notification register.
write(2)
If count is smaller than four, write(2) returns -1 and sets
errno to EINVAL. Otherwise, a four-byte value is copied from
the data buffer, updating the value of the specified signal
notification register. The signal notification register will
either be replaced with the input data or will be updated to the
bitwise OR operation of the old value and the input data,
depending on the contents of the signal1_type or signal2_type
files respectively.
/signal1_type, /signal2_type
These two files change the behavior of the signal1 and signal2
notification files. They contain a numeric ASCII string which is read
as either "1" or "0". In mode 0 (overwrite), the hardware replaces the
contents of the signal channel with the data that is written to it. In
mode 1 (logical OR), the hardware accumulates the bits that are
subsequently written to it. The possible operations on an open
signal1_type or signal2_type file are:
read(2)
When the count supplied to the read(2) call is shorter than the
required length for the digit (plus a newline character),
subsequent reads from the same file descriptor will complete the
string. When a complete string has been read, all subsequent
read operations will return zero bytes and a new file descriptor
needs to be opened to read the value again.
write(2)
A write(2) operation on the file sets the register to the value
given in the string. The string is parsed from the beginning
until the first nonnumeric character or the end of the buffer.
Subsequent writes to the same file descriptor overwrite the
previous setting.
/mbox_info, /ibox_info, /wbox_info, /dma_into, /proxydma_info
Read-only files that contain the saved state of the SPU mailboxes and
DMA queues. This allows the SPU status to be inspected, mainly for
debugging. The mbox_info and ibox_info files each contain the four-
byte mailbox message that has been written by the SPU. If no message
has been written to these mailboxes, then contents of these files is
undefined. The mbox_stat, ibox_stat and wbox_stat files contain the
available message count.
The wbox_info file contains an array of four-byte mailbox messages,
which have been sent to the SPU. With current CBEA machines, the array
is four items in length, so up to 4 * 4 = 16 bytes can be read from
this file. If any mailbox queue entry is empty, then the bytes read at
the corresponding location are undefined.
The dma_info file contains the contents of the SPU MFC DMA queue,
represented as the following structure:
struct spu_dma_info {
uint64_t dma_info_type;
uint64_t dma_info_mask;
uint64_t dma_info_status;
uint64_t dma_info_stall_and_notify;
uint64_t dma_info_atomic_command_status;
struct mfc_cq_sr dma_info_command_data[16];
};
The last member of this data structure is the actual DMA queue,
containing 16 entries. The mfc_cq_sr structure is defined as:
struct mfc_cq_sr {
uint64_t mfc_cq_data0_RW;
uint64_t mfc_cq_data1_RW;
uint64_t mfc_cq_data2_RW;
uint64_t mfc_cq_data3_RW;
};
The proxydma_info file contains similar information, but describes the
proxy DMA queue (i.e., DMAs initiated by entities outside the SPU)
instead. The file is in the following format:
struct spu_proxydma_info {
uint64_t proxydma_info_type;
uint64_t proxydma_info_mask;
uint64_t proxydma_info_status;
struct mfc_cq_sr proxydma_info_command_data[8];
};
Accessing these files requires that the SPU context is scheduled out -
frequent use can be inefficient. These files should not be used for
normal program operation.
These files are not present on contexts that have been created with the
SPU_CREATE_NOSCHED flag.
/cntl This file provides access to the SPU Run Control and SPU status
registers, as an ASCII string. The following operations are supported:
read(2)
Reads from the cntl file will return an ASCII string with the
hex value of the SPU Status register.
write(2)
Writes to the cntl file will set the context's SPU Run Control
register.
/mfc Provides access to the Memory Flow Controller of the SPU. Reading from
the file returns the contents of the SPU's MFC Tag Status register, and
writing to the file initiates a DMA from the MFC. The following
operations are supported:
write(2)
Writes to this file need to be in the format of a MFC DMA
command, defined as follows:
struct mfc_dma_command {
int32_t pad; /* reserved */
uint32_t lsa; /* local storage address */
uint64_t ea; /* effective address */
uint16_t size; /* transfer size */
uint16_t tag; /* command tag */
uint16_t class; /* class ID */
uint16_t cmd; /* command opcode */
};
Writes are required to be exactly sizeof(struct mfc_dma_command)
bytes in size. The command will be sent to the SPU's MFC proxy
queue, and the tag stored in the kernel (see below).
read(2)
Reads the contents of the tag status register. If the file is
opened in blocking mode (i.e., without O_NONBLOCK), then the
read will block until a DMA tag (as performed by a previous
write) is complete. In nonblocking mode, the MFC tag status
register will be returned without waiting.
poll(2)
Calling poll(2) on the mfc file will block until a new DMA can
be started (by checking for POLLOUT) or until a previously
started DMA (by checking for POLLIN) has been completed.
/mss Provides access to the MFC MultiSource Synchronization
(MSS) facility. By mmap(2)-ing this file, processes can access
the MSS area of the SPU.
The following operations are supported:
mmap(2)
Mapping mss into the process address space gives access to the
SPU MSS area within the process address space. Only MAP_SHARED
mappings are allowed.
/psmap Provides access to the whole problem-state mapping of the SPU.
Applications can use this area to interface to the SPU, rather than
writing to individual register files in spufs.
The following operations are supported:
mmap(2)
Mapping psmap gives a process a direct map of the SPU problem
state area. Only MAP_SHARED mappings are supported.
/phys-id
Read-only file containing the physical SPU number that the SPU context
is running on. When the context is not running, this file contains the
string "-1".
The physical SPU number is given by an ASCII hex string.
/object-id
Allows applications to store (or retrieve) a single 64-bit ID into the
context. This ID is later used by profiling tools to uniquely identify
the context.
write(2)
By writing an ASCII hex value into this file, applications can
set the object ID of the SPU context. Any previous value of the
object ID is overwritten.
read(2)
Reading this file gives an ASCII hex string representing the
object ID for this SPU context.
/etc/fstab entry
none /spu spufs gid=spu 0 0
close(2), spu_create(2), spu_run(2), capabilities(7), The Cell Broadband
Engine Architecture (CBEA) specification
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2007-12-20 SPUFS(7)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface