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

NAME
       spufs - 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 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‐
		     ging.

	      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 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
		     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) when‐
		     ever 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 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.

	      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 noti‐
		     fication  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 con‐
		     tents of the signal1_type or signal2_type	files  respec‐
		     tively.

       /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 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];
		  };

	      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.	 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
		     file  is  opened  in  blocking mode (i.e., without O_NON‐
		     BLOCK), then the read will block until a DMA tag (as per‐
		     formed  by a previous write) is complete.	In nonblocking
		     mode, the MFC tag status register will be returned	 with‐
		     out 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  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 Broadband Engine Architecture (CBEA) specification

COLOPHON
       This  page  is  part of release 3.44 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/.

Linux				  2007-12-20			      SPUFS(7)
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