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

NAME
       spufs - SPU filesystem

DESCRIPTION
       The  SPU  filesystem  is used on PowerPC machines that implement the Cell Broadband Engine
       Architecture in order to access Synergistic Processor Units (SPUs).

       The filesystem provides a name space similar to POSIX shared  memory  or  message  queues.
       Users that have write permissions on the filesystem 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=
              Set the user owning the mount point; the default is 0 (root).

       gid=
              Set the group owning the mount point; the default is 0 (root).

       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  regu‐
       lar  filesystems.   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 sup‐
       port  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  con‐
              text.  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 con‐
              tains 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_CRE‐
              ATE_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 be used only 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 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 buf‐
                     fer 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  chan‐
              nel  (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  avail‐
                     able 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 oper‐
              ations 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—that is, 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 - valid only 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  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_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 cur‐
                     rent 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  cur‐
                     rent 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 notifica‐
                     tion 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  sig‐
              nal1_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  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 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  writ‐
              ten  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_CRE‐
              ATE_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 nonblocking
                     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  over‐
                     written.

              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 4.04 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at http://www.kernel.org/doc/man-pages/.

Linux                                       2007-12-20                                   SPUFS(7)

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