# spufs

## 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= <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.
    


## EXAMPLES



           To automatically mount(8) the SPU filesystem when booting, at the
           location _/spu_ chosen by the user, put this line into the fstab(5)
           configuration file:
           none /spu spufs gid=spu 0 0
    


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