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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 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 the files, but  can’t
       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).

       mode=<mode>
              Set  the  mode  of the top-level directory in spufs, as an octal
              mode string.  The default is 0775.

   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 standard behavior
       described 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
       for  the  latter  call,  the only fields of the returned stat structure
       that contain reliable information are st_mode,  st_nlink,  st_uid,  and
       st_gid.

       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:

       /capabilities
              Contains  a comma-delimited string representing the capabilities
              of this SPU context.  Possible capabilities are:

              sched  This context may be scheduled.

              step   This  context  can  be  run  in  single-step  mode,   for
                     debugging.

              New capabilities flags may be added in the future.

       /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 usual, with the exception that lseek(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 is normally 256 kilobytes.

              mmap(2)
                     Mapping  mem  into  the  process  address  space provides
                     access to  the  SPU  local  storage  within  the  process
                     address space.  Only MAP_SHARED mappings are allowed.

       /regs  Contains the saved general-purpose registers of the SPU context.
              This file contains the 128-bit values  of  each  register,  from
              register  0 to register 127, in order.  This allows the general-
              purpose registers to be inspected for debugging.

              Reading to or writing from this file requires that  the  context
              is  scheduled  out,  so  use  of this file is not recommended in
              normal program operation.

              The regs file is not present on contexts that have been  created
              with the SPU_CREATE_NOSCHED flag.

       /mbox  The  first SPU-to-CPU communication mailbox.  This file is read-
              only and can be read in units of 4 bytes.  The file can only  be
              used in non-blocking mode - even poll(2) cannot be used to block
              on this file.  The only possible operation on an open mbox  file
              is:

              read(2)
                     If  count  is  smaller  than four, read(2) returns -1 and
                     sets errno to EINVAL.  If there is no data  available  in
                     the  mailbox  (i.e.,  the  SPU  has  not  sent  a mailbox
                     message), the return value is set to -1 and errno is  set
                     to  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,  thus calling read(2) on an open ibox file will block
              until the SPU has written data to its interrupt mailbox  channel
              (unless  the  file  has been opened with O_NONBLOCK, see below).
              Also, poll(2) and similar system calls can be  used  to  monitor
              for the presence of mailbox data.

              The possible operations on an open ibox file are:

              read(2)
                     If  count  is  smaller  than four, read(2) returns -1 and
                     sets errno to EINVAL.  If there is no data  available  in
                     the  mailbox and the file descriptor has been opened with
                     O_NONBLOCK, the return value is set to -1  and  errno  is
                     set to EAGAIN.

                     If there is no data available in the mailbox 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 communication mailbox.  It is write-only and can
              be written in units of four bytes.   If  the  mailbox  is  full,
              write(2)  will block, and poll(2) can be used to block until the
              mailbox is available for writing again.  The possible operations
              on an open wbox file are:

              write(2)
                     If  count  is  smaller than four, write(2) returns -1 and
                     sets errno to EINVAL.  If there is no space available  in
                     the  mailbox and the file descriptor has been opened with
                     O_NONBLOCK, the return value is set to -1  and  errno  is
                     set to EAGAIN.

                     If  there  is  no  space available in the mailbox and the
                     file descriptor has been opened without  O_NONBLOCK,  the
                     call will block until the SPU reads from its PPE (PowerPC
                     Processing Element) mailbox channel.  When data has  been
                     written successfully, the system call returns four as its
                     function result.

              poll(2)
                     A poll on the wbox file returns  (POLLOUT  |  POLLWRNORM)
                     whenever space is available for writing.

       /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
              mbox  or  ibox  or how many words can be written to wbox without
              blocking.  The files can be read only  in  four-byte  units  and
              return  a  big-endian  binary integer number.  The only possible
              operation on an open *box_stat file is:

              read(2)
                     If count is smaller than four,  read(2)  returns  -1  and
                     sets  errno  to  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  mbox_stat  and
                     ibox_stat) or written to (for wbox_stat)  the  respective
                     mailbox without blocking or returning an EAGAIN error.

       /npc,  /decr,  /decr_status, /spu_tag_mask, /event_mask, /event_status,
       /srr0, /lslr
              Internal  registers  of  the  SPU.  These files contain an ASCII
              string representing the hex value  of  the  specified  register.
              Reads  and  writes  on  these  files (except for npc, see below)
              require that the SPU  context  be  scheduled  out,  so  frequent
              access  to  these  files  is  not recommended for normal program
              operation.

              The contents of these files are:

              npc             Next Program Counter - only valid when  the  SPU
                              is in a stopped state.

              decr            SPU Decrementer

              decr_status     Decrementer Status

              spu_tag_mask    MFC tag mask for SPU DMA

              event_mask      Event mask for SPU interrupts

              event_status    Number of SPU events pending (read-only)

              srr0            Interrupt Return address register

              lslr            Local Store Limit Register

              The possible operations on these files are:

              read(2)
                     Reads  the current register value.  If the register value
                     is larger than the buffer passed to  the  read(2)  system
                     call,  subsequent  reads  will  continue reading from the
                     same buffer, until the end of the buffer is reached.

                     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.

              write(2)
                     A 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.

                     Except for the npc file, these files are not  present  on
                     contexts    that    have    been    created    with   the
                     SPU_CREATE_NOSCHED flag.

       /fpcr  This file provides access  to  the  Floating  Point  Status  and
              Control  Register  (fcpr)  as  a  binary,  four-byte  file.  The
              operations on the fpcr file are:

              read(2)
                     If count is smaller than four,  read(2)  returns  -1  and
                     sets  errno  to  EINVAL.  Otherwise, a four-byte value is
                     placed in the data buffer; this is the current  value  of
                     the fpcr register.

              write(2)
                     If  count  is  smaller than four, write(2) 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 files provide access to the two signal notification channels
              of an SPU.  These are read-write files that operate on four-byte
              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 signal1 or  signal2
              file are:

              read(2)
                     If  count  is  smaller  than four, read(2) returns -1 and
                     sets errno to EINVAL.  Otherwise, a  four-byte  value  is
                     placed  in  the data buffer; this is the current value of
                     the specified signal notification register.

              write(2)
                     If count is smaller than four, write(2)  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 operation
                     of the old value and the input  data,  depending  on  the
                     contents   of  the  signal1_type  or  signal2_type  files
                     respectively.

       /signal1_type, /signal2_type
              These two files change the behavior of the signal1  and  signal2
              notification  files.   They contain a numeric 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(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.

              write(2)
                     A 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.

       /mbox_info, /ibox_info, /wbox_info, /dma_into, /proxydma_info
              Read-only  files  that  contain  the  saved  state  of  the  SPU
              mailboxes and DMA queues.  This allows  the  SPU  status  to  be
              inspected,  mainly  for  debugging.  The mbox_info and ibox_info
              files each contain the four-byte mailbox message that  has  been
              written  by  the  SPU.   If no message has been written to these
              mailboxes, then contents  of  these  files  is  undefined.   The
              mbox_stat,  ibox_stat  and wbox_stat files contain the available
              message count.

              The wbox_info  file  contains  an  array  of  four-byte  mailbox
              messages,  which  have  been sent to the SPU.  With current CBEA
              machines, the array is four items in length, so up to 4 * 4 = 16
              bytes can be read from this file.  If any mailbox queue entry is
              empty, then the bytes read at  the  corresponding  location  are
              undefined.

              The  dma_info  file  contains  the  contents  of the SPU MFC DMA
              queue, represented as the following structure:

                  struct spu_dma_info {
                      uint64_t         dma_info_type;
                      uint64_t         dma_info_mask;
                      uint64_t         dma_info_status;
                      uint64_t         dma_info_stall_and_notify;
                      uint64_t         dma_info_atomic_command_status;
                      struct mfc_cq_sr dma_info_command_data[16];
                  };

              The last member of this data structure is the actual DMA  queue,
              containing 16 entries.  The mfc_cq_sr structure is defined as:

                  struct mfc_cq_sr {
                      uint64_t mfc_cq_data0_RW;
                      uint64_t mfc_cq_data1_RW;
                      uint64_t mfc_cq_data2_RW;
                      uint64_t mfc_cq_data3_RW;
                  };

              The   proxydma_info   file  contains  similar  information,  but
              describes the proxy DMA queue (i.e., DMAs initiated by  entities
              outside the SPU) instead.  The file is in the following format:

                  struct spu_proxydma_info {
                      uint64_t         proxydma_info_type;
                      uint64_t         proxydma_info_mask;
                      uint64_t         proxydma_info_status;
                      struct mfc_cq_sr proxydma_info_command_data[8];
                  };

              Accessing these files requires that the SPU context is scheduled
              out - frequent use can be inefficient.  These files  should  not
              be used for normal program operation.

              These  files  are not present on contexts that have been created
              with the SPU_CREATE_NOSCHED flag.

       /cntl  This file provides access to the SPU Run Control and SPU  status
              registers,  as  an  ASCII  string.  The following operations are
              supported:

              read(2)
                     Reads from the cntl file will return an ASCII string with
                     the hex value of the SPU Status register.

              write(2)
                     Writes  to  the  cntl file will set the context’s SPU Run
                     Control register.

       /mfc   Provides access to  the  Memory  Flow  Controller  of  the  SPU.
              Reading  from the file returns the contents of the SPU’s MFC Tag
              Status register, and writing to the file initiates  a  DMA  from
              the MFC.  The following operations are supported:

              write(2)
                     Writes to this file need to be in the format of a MFC DMA
                     command, defined as follows:

                         struct mfc_dma_command {
                             int32_t  pad;    /* reserved */
                             uint32_t lsa;    /* local storage address */
                             uint64_t ea;     /* effective address */
                             uint16_t size;   /* transfer size */
                             uint16_t tag;    /* command tag */
                             uint16_t class;  /* class ID */
                             uint16_t cmd;    /* command opcode */
                         };

                     Writes  are  required   to   be   exactly   sizeof(struct
                     mfc_dma_command) bytes in size.  The command will be sent
                     to the SPU’s MFC proxy queue, and the tag stored  in  the
                     kernel (see below).

              read(2)
                     Reads  the  contents  of the tag status register.  If the
                     file  is  opened  in   blocking   mode   (i.e.,   without
                     O_NONBLOCK), then the read will block until a DMA tag (as
                     performed by a previous  write)  is  complete.   In  non-
                     blocking  mode,  the  MFC  tag  status  register  will be
                     returned without waiting.

              poll(2)
                     Calling poll(2) on the mfc file will block  until  a  new
                     DMA  can  be started (by checking for POLLOUT) or until a
                     previously started DMA (by checking for POLLIN) has  been
                     completed.

                     /mss    Provides    access   to   the   MFC   MultiSource
                     Synchronization  (MSS)  facility.   By  mmap(2)-ing  this
                     file, processes can access the MSS area of the SPU.

                     The following operations are supported:

              mmap(2)
                     Mapping  mss  into the process address space gives access
                     to the SPU MSS area within  the  process  address  space.
                     Only MAP_SHARED mappings are allowed.

       /psmap Provides  access  to the whole problem-state mapping of the SPU.
              Applications can use this area to interface to the  SPU,  rather
              than writing to individual register files in spufs.

              The following operations are supported:

              mmap(2)
                     Mapping  psmap  gives  a  process a direct map of the SPU
                     problem  state  area.   Only  MAP_SHARED   mappings   are
                     supported.

       /phys-id
              Read-only  file  containing the physical SPU number that the SPU
              context is running on.  When the context is  not  running,  this
              file contains the string "-1".

              The physical SPU number is given by an ASCII hex string.

       /object-id
              Allows  applications  to  store (or retrieve) a single 64-bit ID
              into the context.  This ID is later used by profiling  tools  to
              uniquely identify the context.

              write(2)
                     By   writing   an   ASCII   hex  value  into  this  file,
                     applications can set the object ID of  the  SPU  context.
                     Any previous value of the object ID is overwritten.

              read(2)
                     Reading  this file gives an ASCII hex string representing
                     the object ID for this SPU context.

EXAMPLE

       /etc/fstab  entry
              none      /spu      spufs     gid=spu   0    0

SEE ALSO

       close(2),  spu_create(2),   spu_run(2),   capabilities(7),   The   Cell
       Broadband Engine Architecture (CBEA) specification

COLOPHON

       This  page  is  part of release 3.21 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.