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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 writ‐
       ten 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)
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