path: root/Documentation/filesystems/spufs.txt

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  family 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 and 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  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 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 occurred 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)