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linux/Documentation/filesystems/spufs.txt
Arnd Bergmann 67207b9664 [PATCH] spufs: The SPU file system, base 
This is the current version of the spu file system, used
for driving SPEs on the Cell Broadband Engine.

This release is almost identical to the version for the
2.6.14 kernel posted earlier, which is available as part
of the Cell BE Linux distribution from
http://www.bsc.es/projects/deepcomputing/linuxoncell/.

The first patch provides all the interfaces for running
spu application, but does not have any support for
debugging SPU tasks or for scheduling. Both these
functionalities are added in the subsequent patches.

See Documentation/filesystems/spufs.txt on how to use
spufs.

Signed-off-by: Arnd Bergmann <arndb@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
2006-01-09 14:49:12 +11:00

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SPUFS(2) Linux Programmer's Manual SPUFS(2)
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 familiy 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 can 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 writting 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 or 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)
Linux 2005-09-28 SPUFS(2)
------------------------------------------------------------------------------
SPU_RUN(2) Linux Programmer's Manual SPU_RUN(2)
NAME
spu_run - execute an spu context
SYNOPSIS
#include <sys/spu.h>
int spu_run(int fd, unsigned int *npc, unsigned int *event);
DESCRIPTION
The spu_run system call is used on PowerPC machines that implement the
Cell Broadband Engine Architecture in order to access Synergistic Pro-
cessor Units (SPUs). It uses the fd that was returned from spu_cre-
ate(2) to address a specific SPU context. When the context gets sched-
uled to a physical SPU, it starts execution at the instruction pointer
passed in npc.
Execution of SPU code happens synchronously, meaning that spu_run does
not return while the SPU is still running. If there is a need to exe-
cute SPU code in parallel with other code on either the main CPU or
other SPUs, you need to create a new thread of execution first, e.g.
using the pthread_create(3) call.
When spu_run returns, the current value of the SPU instruction pointer
is written back to npc, so you can call spu_run again without updating
the pointers.
event can be a NULL pointer or point to an extended status code that
gets filled when spu_run returns. It can be one of the following con-
stants:
SPE_EVENT_DMA_ALIGNMENT
A DMA alignment error
SPE_EVENT_SPE_DATA_SEGMENT
A DMA segmentation error
SPE_EVENT_SPE_DATA_STORAGE
A DMA storage error
If NULL is passed as the event argument, these errors will result in a
signal delivered to the calling process.
RETURN VALUE
spu_run returns the value of the spu_status register or -1 to indicate
an error and set errno to one of the error codes listed below. The
spu_status register value contains a bit mask of status codes and
optionally a 14 bit code returned from the stop-and-signal instruction
on the SPU. The bit masks for the status codes are:
0x02 SPU was stopped by stop-and-signal.
0x04 SPU was stopped by halt.
0x08 SPU is waiting for a channel.
0x10 SPU is in single-step mode.
0x20 SPU has tried to execute an invalid instruction.
0x40 SPU has tried to access an invalid channel.
0x3fff0000
The bits masked with this value contain the code returned from
stop-and-signal.
There are always one or more of the lower eight bits set or an error
code is returned from spu_run.
ERRORS
EAGAIN or EWOULDBLOCK
fd is in non-blocking mode and spu_run would block.
EBADF fd is not a valid file descriptor.
EFAULT npc is not a valid pointer or status is neither NULL nor a valid
pointer.
EINTR A signal occured while spu_run was in progress. The npc value
has been updated to the new program counter value if necessary.
EINVAL fd is not a file descriptor returned from spu_create(2).
ENOMEM Insufficient memory was available to handle a page fault result-
ing from an MFC direct memory access.
ENOSYS the functionality is not provided by the current system, because
either the hardware does not provide SPUs or the spufs module is
not loaded.
NOTES
spu_run is meant to be used from libraries that implement a more
abstract interface to SPUs, not to be used from regular applications.
See http://www.bsc.es/projects/deepcomputing/linuxoncell/ for the rec-
ommended libraries.
CONFORMING TO
This call is Linux specific and only implemented by the ppc64 architec-
ture. Programs using this system call are not portable.
BUGS
The code does not yet fully implement all features lined out here.
AUTHOR
Arnd Bergmann <arndb@de.ibm.com>
SEE ALSO
capabilities(7), close(2), spu_create(2), spufs(7)
Linux 2005-09-28 SPU_RUN(2)
------------------------------------------------------------------------------
SPU_CREATE(2) Linux Programmer's Manual SPU_CREATE(2)
NAME
spu_create - create a new spu context
SYNOPSIS
#include <sys/types.h>
#include <sys/spu.h>
int spu_create(const char *pathname, int flags, mode_t mode);
DESCRIPTION
The spu_create system call is used on PowerPC machines that implement
the Cell Broadband Engine Architecture in order to access Synergistic
Processor Units (SPUs). It creates a new logical context for an SPU in
pathname and returns a handle to associated with it. pathname must
point to a non-existing directory in the mount point of the SPU file
system (spufs). When spu_create is successful, a directory gets cre-
ated on pathname and it is populated with files.
The returned file handle can only be passed to spu_run(2) or closed,
other operations are not defined on it. When it is closed, all associ-
ated directory entries in spufs are removed. When the last file handle
pointing either inside of the context directory or to this file
descriptor is closed, the logical SPU context is destroyed.
The parameter flags can be zero or any bitwise or'd combination of the
following constants:
SPU_RAWIO
Allow mapping of some of the hardware registers of the SPU into
user space. This flag requires the CAP_SYS_RAWIO capability, see
capabilities(7).
The mode parameter specifies the permissions used for creating the new
directory in spufs. mode is modified with the user's umask(2) value
and then used for both the directory and the files contained in it. The
file permissions mask out some more bits of mode because they typically
support only read or write access. See stat(2) for a full list of the
possible mode values.
RETURN VALUE
spu_create returns a new file descriptor. It may return -1 to indicate
an error condition and set errno to one of the error codes listed
below.
ERRORS
EACCESS
The current user does not have write access on the spufs mount
point.
EEXIST An SPU context already exists at the given path name.
EFAULT pathname is not a valid string pointer in the current address
space.
EINVAL pathname is not a directory in the spufs mount point.
ELOOP Too many symlinks were found while resolving pathname.
EMFILE The process has reached its maximum open file limit.
ENAMETOOLONG
pathname was too long.
ENFILE The system has reached the global open file limit.
ENOENT Part of pathname could not be resolved.
ENOMEM The kernel could not allocate all resources required.
ENOSPC There are not enough SPU resources available to create a new
context or the user specific limit for the number of SPU con-
texts has been reached.
ENOSYS the functionality is not provided by the current system, because
either the hardware does not provide SPUs or the spufs module is
not loaded.
ENOTDIR
A part of pathname is not a directory.
NOTES
spu_create is meant to be used from libraries that implement a more
abstract interface to SPUs, not to be used from regular applications.
See http://www.bsc.es/projects/deepcomputing/linuxoncell/ for the rec-
ommended libraries.
FILES
pathname must point to a location beneath the mount point of spufs. By
convention, it gets mounted in /spu.
CONFORMING TO
This call is Linux specific and only implemented by the ppc64 architec-
ture. Programs using this system call are not portable.
BUGS
The code does not yet fully implement all features lined out here.
AUTHOR
Arnd Bergmann <arndb@de.ibm.com>
SEE ALSO
capabilities(7), close(2), spu_run(2), spufs(7)
Linux 2005-09-28 SPU_CREATE(2)
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