274 lines
12 KiB
ReStructuredText
274 lines
12 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
=====
|
|
spufs
|
|
=====
|
|
|
|
Name
|
|
====
|
|
|
|
spufs - the SPU file system
|
|
|
|
|
|
Description
|
|
===========
|
|
|
|
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 in the spufs root.
|
|
|
|
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 those files, but not actu-
|
|
ally add or remove files.
|
|
|
|
|
|
Mount Options
|
|
=============
|
|
|
|
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).
|
|
|
|
|
|
Files
|
|
=====
|
|
|
|
The files in spufs mostly follow the standard behavior for regular sys-
|
|
tem 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 behaviour 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
|
|
only the st_mode, st_nlink, st_uid and st_gid fields of struct stat
|
|
contain reliable information.
|
|
|
|
All files support the chmod(2)/fchmod(2) and chown(2)/fchown(2) opera-
|
|
tions, 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:
|
|
|
|
|
|
/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 documented, with the exception that seek(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 normally is 256 kilobytes.
|
|
|
|
mmap(2)
|
|
Mapping mem into the process address space gives access to the
|
|
SPU local storage within the process address space. Only
|
|
MAP_SHARED mappings are allowed.
|
|
|
|
|
|
/mbox
|
|
The first SPU to CPU communication mailbox. This file is read-only and
|
|
can be read in units of 32 bits. The file can only be used in non-
|
|
blocking mode and it even poll() will not block on it. The possible
|
|
operations on an open mbox file are:
|
|
|
|
read(2)
|
|
If a count smaller than four is requested, read returns -1 and
|
|
sets errno to EINVAL. If there is no data available in the mail
|
|
box, the return value is set to -1 and errno becomes 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, and the
|
|
poll family of system calls can be used to wait for it. The possible
|
|
operations on an open ibox file are:
|
|
|
|
read(2)
|
|
If a count smaller than four is requested, read returns -1 and
|
|
sets errno to EINVAL. If there is no data available in the mail
|
|
box and the file descriptor has been opened with O_NONBLOCK, the
|
|
return value is set to -1 and errno becomes EAGAIN.
|
|
|
|
If there is no data available in the mail box 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 communation mailbox. It is write-only and can be written
|
|
in units of 32 bits. If the mailbox is full, write() will block and
|
|
poll can be used to wait for it becoming empty again. The possible
|
|
operations on an open wbox file are: write(2) If a count smaller than
|
|
four is requested, write returns -1 and sets errno to EINVAL. If there
|
|
is no space available in the mail box and the file descriptor has been
|
|
opened with O_NONBLOCK, the return value is set to -1 and errno becomes
|
|
EAGAIN.
|
|
|
|
If there is no space available in the mail box and the file descriptor
|
|
has been opened without O_NONBLOCK, the call will block until the SPU
|
|
reads from its PPE mailbox channel. When data has been read success-
|
|
fully, four bytes are placed in the data buffer and the value four is
|
|
returned.
|
|
|
|
poll(2)
|
|
Poll on the ibox file returns (POLLOUT | POLLWRNORM) whenever
|
|
space is available for writing.
|
|
|
|
|
|
/mbox_stat, /ibox_stat, /wbox_stat
|
|
Read-only files that contain the length of the current queue, 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 4-byte
|
|
units and return a big-endian binary integer number. The possible
|
|
operations on an open ``*box_stat`` file are:
|
|
|
|
read(2)
|
|
If a count smaller than four is requested, read returns -1 and
|
|
sets errno to EINVAL. Otherwise, a four byte value is placed in
|
|
the data buffer, containing the number of elements that can be
|
|
read from (for mbox_stat and ibox_stat) or written to (for
|
|
wbox_stat) the respective mail box without blocking or resulting
|
|
in EAGAIN.
|
|
|
|
|
|
/npc, /decr, /decr_status, /spu_tag_mask, /event_mask, /srr0
|
|
Internal registers of the SPU. The representation is an ASCII string
|
|
with the numeric value of the next instruction to be executed. These
|
|
can be used in read/write mode for debugging, but normal operation of
|
|
programs should not rely on them because access to any of them except
|
|
npc requires an SPU context save and is therefore very inefficient.
|
|
|
|
The contents of these files are:
|
|
|
|
=================== ===================================
|
|
npc Next Program Counter
|
|
decr SPU Decrementer
|
|
decr_status Decrementer Status
|
|
spu_tag_mask MFC tag mask for SPU DMA
|
|
event_mask Event mask for SPU interrupts
|
|
srr0 Interrupt Return address register
|
|
=================== ===================================
|
|
|
|
|
|
The possible operations on an open npc, decr, decr_status,
|
|
spu_tag_mask, event_mask or srr0 file are:
|
|
|
|
read(2)
|
|
When the count supplied to the read call is shorter than the
|
|
required length for the pointer value plus a newline character,
|
|
subsequent reads from the same file descriptor will result in
|
|
completing the string, regardless of changes to the register by
|
|
a running SPU task. 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 operation on the file results in setting the register to
|
|
the value given in the string. The string is parsed from the
|
|
beginning to the first non-numeric character or the end of the
|
|
buffer. Subsequent writes to the same file descriptor overwrite
|
|
the previous setting.
|
|
|
|
|
|
/fpcr
|
|
This file gives access to the Floating Point Status and Control Regis-
|
|
ter as a four byte long file. The operations on the fpcr file are:
|
|
|
|
read(2)
|
|
If a count smaller than four is requested, read returns -1 and
|
|
sets errno to EINVAL. Otherwise, a four byte value is placed in
|
|
the data buffer, containing the current value of the fpcr regis-
|
|
ter.
|
|
|
|
write(2)
|
|
If a count smaller than four is requested, write 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 two signal notification channels of an SPU. These are read-write
|
|
files that operate on a 32 bit word. 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 sig-
|
|
nal2 file are:
|
|
|
|
read(2)
|
|
If a count smaller than four is requested, read returns -1 and
|
|
sets errno to EINVAL. Otherwise, a four byte value is placed in
|
|
the data buffer, containing the current value of the specified
|
|
signal notification register.
|
|
|
|
write(2)
|
|
If a count smaller than four is requested, write 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 of the old value and the input data, depending on the
|
|
contents of the signal1_type, or signal2_type respectively,
|
|
file.
|
|
|
|
|
|
/signal1_type, /signal2_type
|
|
These two files change the behavior of the signal1 and signal2 notifi-
|
|
cation files. The contain a numerical 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 subse-
|
|
quently 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 call is shorter than the
|
|
required length for the digit plus a newline character, subse-
|
|
quent reads from the same file descriptor will result in com-
|
|
pleting 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 operation on the file results in setting the register to
|
|
the value given in the string. The string is parsed from the
|
|
beginning to the first non-numeric character or the end of the
|
|
buffer. Subsequent writes to the same file descriptor overwrite
|
|
the previous setting.
|
|
|
|
|
|
Examples
|
|
========
|
|
/etc/fstab entry
|
|
none /spu spufs gid=spu 0 0
|
|
|
|
|
|
Authors
|
|
=======
|
|
Arnd Bergmann <arndb@de.ibm.com>, Mark Nutter <mnutter@us.ibm.com>,
|
|
Ulrich Weigand <Ulrich.Weigand@de.ibm.com>
|
|
|
|
See Also
|
|
========
|
|
capabilities(7), close(2), spu_create(2), spu_run(2), spufs(7)
|