spufs


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 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 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) 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:

       /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  debug-
                     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 nor-
              mal 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 nonblocking 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 mes-
                     sage), 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 simi-
              lar 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

              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

              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 descrip-
                     tor 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 nonnumeric 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_CRE-
                     ATE_NOSCHED flag.

       /fpcr  This  file provides access to the Floating Point Status and Con-
              trol Register (fcpr) as a binary, four-byte  file.   The  opera-
              tions 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.

              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 hard-
              ware 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  descrip-
                     tor 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 nonnumeric 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  mail-
              boxes  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 mes-
              sages, 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];
                  };

              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.  Read-
              ing from the file returns the contents of the SPU's MFC Tag Sta-
              tus  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
                     /mss Provides access to the MFC MultiSource  Synchroniza-
                     tion (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 sup-
                     ported.

       /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,  applica-
                     tions can set the object ID of the SPU context.  Any pre-
                     vious 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 Broad-
       band Engine Architecture (CBEA) specification

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