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 actually
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 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 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)
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:
/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:
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.
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:
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:
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 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 successfully, four bytes are placed in
the data buffer and the value four is returned.
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:
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:
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.
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 Register as a four byte long file. The operations
on the
fpcr
file are:
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 register.
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
signal2
file are:
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.
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 notification 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 subsequently written to it.
The possible operations on an open
signal1_type
or
signal2_type
file are:
When the count supplied to the
read
call is shorter than the required length for the digit
plus a newline character, subsequent reads from the same
file descriptor will result in completing 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.
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.
