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spufs — SPU filesystem
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.
Set the user owning the mount point; the default is 0 (root).
Set the group owning the mount point; the default is 0 (root).
Set the mode of the top-level directory in
spufs
, as
an octal mode string. The default is 0775.
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. OnlyMAP_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 setserrno
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 anderrno
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 setserrno
to EINVAL. If there is no data available in the mailbox and the file descriptor has been opened withO_NONBLOCK
, the return value is set to −1 anderrno
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 setserrno
to EINVAL. If there is no space available in the mailbox and the file descriptor has been opened withO_NONBLOCK
, the return value is set to −1 anderrno
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 setserrno
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 (formbox_stat
andibox_stat
) or written to (forwbox_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 theSPU_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 setserrno
to EINVAL. Otherwise, a four-byte value is placed in the data buffer; this is the current value of thefpcr
register.- write(2)
If
count
is smaller than four, write(2) returns −1 and setserrno
to EINVAL. Otherwise, a four-byte value is copied from the data buffer, updating the value of thefpcr
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 setserrno
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 setserrno
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 thesignal1_type
orsignal2_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:
/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 forPOLLOUT
) or until a previously started DMA (by checking forPOLLIN
) 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. OnlyMAP_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. OnlyMAP_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.
close(2), spu_create(2), spu_run(2), capabilities(7)
The Cell Broadband Engine Architecture (CBEA) specification
This page is part of release 3.54 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/.
Copyright (c) International Business Machines Corp., 2006 %%%LICENSE_START(GPLv2+_SW_3_PARA) This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this manual; if not, see <http://www.gnu.org/licenses/>. %%%LICENSE_END HISTORY: 2005-09-28, created by Arnd Bergmann <arndbde.ibm.com>, Mark Nutter <mnutterus.ibm.com> and Ulrich Weigand <Ulrich.Weigandde.ibm.com> 2006-06-16, revised by Eduardo M. Fleury <efleurybr.ibm.com> 2007-07-10, quite a lot of polishing by mtk 2007-09-28, updates for newer kernels by Jeremy Kerr <jkozlabs.org> |