NAME | DESCRIPTION | EXAMPLE | SEE ALSO | COLOPHON

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

NAME         top

       spufs - SPU filesystem

DESCRIPTION         top

       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=<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 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 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
              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 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—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 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 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
              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
                     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 overwritten.

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

EXAMPLE         top

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

SEE ALSO         top

       close(2), spu_create(2), spu_run(2), capabilities(7)

       The Cell Broadband Engine Architecture (CBEA) specification

COLOPHON         top

       This page is part of release 4.08 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
       https://www.kernel.org/doc/man-pages/.

Linux                            2007-12-20                         SPUFS(7)