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SPUFS(7)                   Linux Programmer's Manual                  SPUFS(7)



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 sup-
       ported 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 per-
       missions 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 capabili-
              ties 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 sup-
                     ported 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 writ-
              ten 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 avail-
              able 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 pos-
              sible 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 opera-
              tion.

              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  noti-
                     fication 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  notifica-
                     tion  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  mail-
              boxes,  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 struc-
              ture:

                  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 ini-
              tiated 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 fol-
              lowing operations are supported:

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

              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 POLL-
                     OUT) 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 inter-
              face 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 map-
                     pings 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  con-
                     text.  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) specifica-
       tion

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2007-12-20                          SPUFS(7)