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 manipu-
       lating 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  sup-
       port  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:

       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  avail-
              able  in  the  mail  box, the return value is set to -1 and errno becomes EAGAIN. When data has been read success-
              fully, 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  avail-
              able  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 successfully, 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  opera-
              tions 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 Register 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 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 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:

       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 sig-
              nal 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:

       read(2)
              When the count supplied to the read call is shorter than the required length for the digit plus a newline  charac-
              ter,  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.

       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 <arndbATde.com>, Mark Nutter <mnutterATus.com>, Ulrich Weigand <Ulrich.WeigandATde.com>

SEE ALSO
       capabilities(7), close(2), spu_create(2), spu_run(2), spufs(7)



Linux                                                      2005-09-28                                                   SPUFS(2)