path: root/man7/spufs.7

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.\" HISTORY:
.\" 2005-09-28, created by Arnd Bergmann <arndb@de.ibm.com>,
.\"   Mark Nutter <mnutter@us.ibm.com> and
.\"   Ulrich Weigand <Ulrich.Weigand@de.ibm.com>
.\" 2006-06-16, revised by Eduardo M. Fleury <efleury@br.ibm.com>
.\" 2007-07-10, quite a lot of polishing by mtk
.\"
.TH SPUFS 7 2007-07-10 "Linux" "Linux Programmer's Manual"
.SH NAME
spufs \- the SPU file system
.SH 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
.BR 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 those files, but can't
add or remove files.
.SS Mount Options
.TP
.B uid=<uid>
set the user owning the mount point; the default is 0 (root).
.TP
.B gid=<gid>
set the group owning the mount point; the default is 0 (root).
.SS Files
The files in
.I spufs
mostly follow the standard behavior for regular system calls like
.BR read (2)
or
.BR 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
.BR read (2)
operation also support
.BR readv (2)
and all files that support the
.BR write (2)
operation also support
.BR writev (2).

All files support the
.BR access (2)
and
.BR stat (2)
family of operations, but for the latter call,
the only fields of the returned
.I stat
structure that contain reliable information are
.IR st_mode ,
.IR st_nlink ,
.IR st_uid ,
and
.IR st_gid .

All files support the
.BR chmod (2)/ fchmod (2)
and
.BR chown (2)/ fchown (2)
operations, but will not be able to grant permissions that contradict
the possible operations (e.g., read access on the
.I wbox
file).

The current set of files is:
.TP
.B /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
.I mem
file are:
.RS
.TP
.BR read "(2), " pread "(2), " write "(2), " pwrite "(2), " lseek (2)
These operate as usual, with the exception that
.BR seek "(2), " write (2)
and
.BR 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.
.TP
.BR mmap (2)
Mapping
.I mem
into the process address space provides access to the SPU local
storage within the process address space.
Only
.B MAP_SHARED
mappings are allowed.
.RE
.TP
.B /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 not
even
.BR poll (2)
will block on it.
The only possible operation on an open
.I mbox
file is:
.RS
.TP
.BR read (2)
If
.I count
is smaller than four,
.BR read (2)
returns \-1 and sets
.I errno
to
.BR EINVAL .
If there is no data available in the mailbox, the return
value is set to \-1 and
.I errno
is set to
.BR EAGAIN .
When data
has been read successfully, four bytes are placed in
the data buffer and the value four is returned.
.RE
.TP
.B /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
.BR poll (2)
and similar system calls can be used to monitor this file.
The possible operations on an open
.I ibox
file are:
.RS
.TP
.BR read (2)
If
.I count
is smaller than four,
.BR read (2)
returns \-1 and sets
.I errno
to
.BR EINVAL .
If there is no data available in the mailbox and the file
descriptor has been opened with
.BR O_NONBLOCK ,
the return value is set to \-1 and
.I errno
is set to
.BR EAGAIN .

If there is no data available in the mailbox and the file
descriptor has been opened without
.BR 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.
.TP
.BR poll (2)
Poll on the
.I ibox
file returns
.I "(POLLIN | POLLRDNORM)"
whenever data is available for reading.
.RE
.TP
.B /wbox
The CPU-to-SPU communication mailbox.
It is write-only and can be written in units of 32 bits.
If the mailbox is full,
.BR write (2)
will block and
.BR poll (2)
can be used to wait for it to become empty again.
The possible operations on an open
.I wbox
file are:
.RS
.TP
.BR write (2)
If
.I count
is smaller than four,
.BR write (2)
returns \-1 and sets
.I errno
to
.BR EINVAL .
If there is no space available in the mailbox and the file
descriptor has been opened with
.BR O_NONBLOCK ,
the return
value is set to \-1 and
.I errno
is set to
.BR EAGAIN .

If there is no space available in the mailbox and the file
descriptor has been opened without
.BR O_NONBLOCK ,
the call will
block until the SPU reads from its PPE mailbox channel.
When data has been written successfully,
the system call returns four as its function result.
.TP
.BR poll (2)
A poll on the
.I wbox
file returns
.I "(POLLOUT | POLLWRNORM)"
whenever space is available for writing.
.RE
.TP
.BR /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
.IR mbox " or " ibox
or how many words can be written to
.I wbox
without blocking.
The files can be read only in four-byte units and return
a big-endian binary integer number.
The possible operations on an open
.I *box_stat
file are:
.RS
.TP
.BR read (2)
If
.I count
is smaller than four,
.BR read (2)
returns \-1 and sets
.I errno
to
.BR 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
.I mbox_stat
and
.IR ibox_stat )
or written to (for
.IR wbox_stat )
the respective mailbox without blocking or getting an
.BR EAGAIN
error.
.RE
.TP
.BR /npc ", " /decr ", " /decr_status ", " /spu_tag_mask ", " \
/event_mask ", " /srr0
These files expose internal registers of the SPU.
The values are represented
as ASCII strings containing the numeric value of each register.
These can be used in read/write mode for debugging, but normal
operation of programs should not rely on these files because
accesses to any of them except
.I npc
require an SPU context save, which is very inefficient.
.IP
The contents of these files are:
.RS
.TP 16
.I npc
Next Program Counter
.TP
.I decr
SPU Decrementer
.TP
.I decr_status
Decrementer Status
.TP
.I spu_tag_mask
MFC tag mask for SPU DMA
.TP
.I event_mask
Event mask for SPU interrupts
.TP
.I srr0
Interrupt Return address register
.RE
.IP
The possible operations on one of these files are:
.RS
.TP
.BR read (2)
When the
.I count
supplied to the
.BR read (2)
call is shorter than the required length for the register
value plus a newline character, subsequent reads from the same
file descriptor will complete 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 a new value.
.TP
.BR write (2)
A
.BR 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 non-numeric character or the end of the buffer.
Subsequent writes to the same file descriptor overwrite the
previous setting.
.RE
.TP
.B /fpcr
This file provides access to the Floating Point Status and
Control Register as a four-byte file.
The operations on the
.I fpcr
file are:
.RS
.TP
.BR read (2)
If
.I count
is smaller than four,
.BR read (2)
returns \-1 and sets
.I errno
to
.BR EINVAL .
Otherwise, a four-byte value is placed in the data buffer;
this is the current value of the
.I fpcr
register.
.TP
.BR write (2)
If
.I count
is smaller than four,
.BR write (2)
returns \-1 and sets
.I errno
to
.BR EINVAL .
Otherwise, a four-byte value is copied from the data buffer,
updating the value of the
.I fpcr
register.
.RE
.TP
.BR /signal1 ", " /signal2
The files provide access to the two signal notification channels
of an SPU.
These are read-write files that operate on 32-bit 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
.I signal1
or
.I signal2
file are:
.RS
.TP
.BR read (2)
If
.I count
is smaller than four,
.BR read (2)
returns \-1 and sets
.I errno
to
.BR EINVAL .
Otherwise, a four-byte value is placed in the data buffer;
this is the current value of the specified signal notification
register.
.TP
.BR write (2)
If
.I count
is smaller than four,
.BR write (2)
returns \-1 and sets
.I errno
to
.BR 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
.IR signal1_type
or
.IR signal2_type
files respectively.
.RE
.TP
.BR /signal1_type ", " /signal2_type
These two files change the behavior of the
.IR signal1
and
.I signal2
notification files.
They 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
.I signal1_type
or
.I signal2_type
file are:
.RS
.TP
.BR read (2)
When the count supplied to the
.BR 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.
.TP
.BR write (2)
A
.BR 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 non-numeric character or the end of the buffer.
Subsequent writes to the same file descriptor overwrite the
previous setting.
.RE
.SH EXAMPLE
.TP
.IR /etc/fstab "  entry"
none  	/spu  	spufs  	gid=spu  	0	0
.\" .SH AUTHORS
.\" Arnd Bergmann <arndb@de.ibm.com>,
.\" Mark Nutter <mnutter@us.ibm.com> and
.\" Ulrich Weigand <Ulrich.Weigand@de.ibm.com>
.SH SEE ALSO
.BR close (2),
.BR spu_create (2),
.BR spu_run (2)