1SPUFS(7) Linux Programmer's Manual SPUFS(7)
2
6 spufs - SPU file system
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9 The SPU file system is used on PowerPC machines that implement the Cell
10 Broadband Engine Architecture in order to access Synergistic Processor
11 Units (SPUs).
12 The file system provides a name space similar to POSIX shared memory or
14 message queues. Users that have write permissions on the file system
15 can use spu_create(2) to establish SPU contexts under the spufs root
16 directory.
17 Every SPU context is represented by a directory containing a predefined
19 set of files. These files can be used for manipulating the state of
20 the logical SPU. Users can change permissions on the files, but can't
21 add or remove files.
22 Mount options
24 uid=<uid>
25 Set the user owning the mount point; the default is 0 (root).
26 gid=<gid>
28 Set the group owning the mount point; the default is 0 (root).
29 mode=<mode>
31 Set the mode of the top-level directory in spufs, as an octal
32 mode string. The default is 0775.
33 Files
35 The files in spufs mostly follow the standard behavior for regular sys‐
36 tem calls like read(2) or write(2), but often support only a subset of
37 the operations supported on regular file systems. This list details
38 the supported operations and the deviations from the standard behavior
39 described in the respective man pages.
40 All files that support the read(2) operation also support readv(2) and
42 all files that support the write(2) operation also support writev(2).
43 All files support the access(2) and stat(2) family of operations, but
44 for the latter call, the only fields of the returned stat structure
45 that contain reliable information are st_mode, st_nlink, st_uid, and
46 st_gid.
47 All files support the chmod(2)/fchmod(2) and chown(2)/fchown(2) opera‐
49 tions, but will not be able to grant permissions that contradict the
50 possible operations (e.g., read access on the wbox file).
51 The current set of files is:
53 /capabilities
55 Contains a comma-delimited string representing the capabilities
56 of this SPU context. Possible capabilities are:
57 sched This context may be scheduled.
59 step This context can be run in single-step mode, for debug‐
61 ging.
62 New capabilities flags may be added in the future.
64 /mem the contents of the local storage memory of the SPU. This can
66 be accessed like a regular shared memory file and contains both
67 code and data in the address space of the SPU. The possible
68 operations on an open mem file are:
69 read(2), pread(2), write(2), pwrite(2), lseek(2)
71 These operate as usual, with the exception that lseek(2),
72 write(2), and pwrite(2) are not supported beyond the end
73 of the file. The file size is the size of the local
74 storage of the SPU, which is normally 256 kilobytes.
75 mmap(2)
77 Mapping mem into the process address space provides
78 access to the SPU local storage within the process
79 address space. Only MAP_SHARED mappings are allowed.
80 /regs Contains the saved general-purpose registers of the SPU context.
82 This file contains the 128-bit values of each register, from
83 register 0 to register 127, in order. This allows the general-
84 purpose registers to be inspected for debugging.
85 Reading to or writing from this file requires that the context
87 is scheduled out, so use of this file is not recommended in nor‐
88 mal program operation.
89 The regs file is not present on contexts that have been created
91 with the SPU_CREATE_NOSCHED flag.
92 /mbox The first SPU-to-CPU communication mailbox. This file is read-
94 only and can be read in units of 4 bytes. The file can be used
95 only in nonblocking mode - even poll(2) cannot be used to block
96 on this file. The only possible operation on an open mbox file
97 is:
98 read(2)
100 If count is smaller than four, read(2) returns -1 and
101 sets errno to EINVAL. If there is no data available in
102 the mailbox (i.e., the SPU has not sent a mailbox mes‐
103 sage), the return value is set to -1 and errno is set to
104 EAGAIN. When data has been read successfully, four bytes
105 are placed in the data buffer and the value four is
106 returned.
107 /ibox The second SPU-to-CPU communication mailbox. This file is simi‐
109 lar to the first mailbox file, but can be read in blocking I/O
110 mode, thus calling read(2) on an open ibox file will block until
111 the SPU has written data to its interrupt mailbox channel
112 (unless the file has been opened with O_NONBLOCK, see below).
113 Also, poll(2) and similar system calls can be used to monitor
114 for the presence of mailbox data.
115 The possible operations on an open ibox file are:
117 read(2)
119 If count is smaller than four, read(2) returns -1 and
120 sets errno to EINVAL. If there is no data available in
121 the mailbox and the file descriptor has been opened with
122 O_NONBLOCK, the return value is set to -1 and errno is
123 set to EAGAIN.
124 If there is no data available in the mailbox and the file
126 descriptor has been opened without O_NONBLOCK, the call
127 will block until the SPU writes to its interrupt mailbox
128 channel. When data has been read successfully, four
129 bytes are placed in the data buffer and the value four is
130 returned.
131 poll(2)
133 Poll on the ibox file returns (POLLIN | POLLRDNORM) when‐
134 ever data is available for reading.
135 /wbox The CPU-to-SPU communication mailbox. It is write-only and can
137 be written in units of four bytes. If the mailbox is full,
138 write(2) will block, and poll(2) can be used to block until the
139 mailbox is available for writing again. The possible operations
140 on an open wbox file are:
141 write(2)
143 If count is smaller than four, write(2) returns -1 and
144 sets errno to EINVAL. If there is no space available in
145 the mailbox and the file descriptor has been opened with
146 O_NONBLOCK, the return value is set to -1 and errno is
147 set to EAGAIN.
148 If there is no space available in the mailbox and the
150 file descriptor has been opened without O_NONBLOCK, the
151 call will block until the SPU reads from its PPE (PowerPC
152 Processing Element) mailbox channel. When data has been
153 written successfully, the system call returns four as its
154 function result.
155 poll(2)
157 A poll on the wbox file returns (POLLOUT | POLLWRNORM)
158 whenever space is available for writing.
159 /mbox_stat, /ibox_stat, /wbox_stat
161 These are read-only files that contain the length of the current
162 queue of each mailbox, i.e., how many words can be read from
163 mbox or ibox or how many words can be written to wbox without
164 blocking. The files can be read only in four-byte units and
165 return a big-endian binary integer number. The only possible
166 operation on an open *box_stat file is:
167 read(2)
169 If count is smaller than four, read(2) returns -1 and
170 sets errno to EINVAL. Otherwise, a four-byte value is
171 placed in the data buffer. This value is the number of
172 elements that can be read from (for mbox_stat and
173 ibox_stat) or written to (for wbox_stat) the respective
174 mailbox without blocking or returning an EAGAIN error.
175 /npc, /decr, /decr_status, /spu_tag_mask, /event_mask, /event_status,
177 /srr0, /lslr
178 Internal registers of the SPU. These files contain an ASCII
179 string representing the hex value of the specified register.
180 Reads and writes on these files (except for npc, see below)
181 require that the SPU context be scheduled out, so frequent
182 access to these files is not recommended for normal program
183 operation.
184 The contents of these files are:
186 npc Next Program Counter - valid only when the SPU
188 is in a stopped state.
189 decr SPU Decrementer
191 decr_status Decrementer Status
193 spu_tag_mask MFC tag mask for SPU DMA
195 event_mask Event mask for SPU interrupts
197 event_status Number of SPU events pending (read-only)
199 srr0 Interrupt Return address register
201 lslr Local Store Limit Register
203 The possible operations on these files are:
205 read(2)
207 Reads the current register value. If the register value
208 is larger than the buffer passed to the read(2) system
209 call, subsequent reads will continue reading from the
210 same buffer, until the end of the buffer is reached.
211 When a complete string has been read, all subsequent read
213 operations will return zero bytes and a new file descrip‐
214 tor needs to be opened to read a new value.
215 write(2)
217 A write(2) operation on the file sets the register to the
218 value given in the string. The string is parsed from the
219 beginning until the first nonnumeric character or the end
220 of the buffer. Subsequent writes to the same file
221 descriptor overwrite the previous setting.
222 Except for the npc file, these files are not present on
224 contexts that have been created with the SPU_CRE‐
225 ATE_NOSCHED flag.
226 /fpcr This file provides access to the Floating Point Status and Con‐
228 trol Register (fcpr) as a binary, four-byte file. The opera‐
229 tions on the fpcr file are:
230 read(2)
232 If count is smaller than four, read(2) returns -1 and
233 sets errno to EINVAL. Otherwise, a four-byte value is
234 placed in the data buffer; this is the current value of
235 the fpcr register.
236 write(2)
238 If count is smaller than four, write(2) returns -1 and
239 sets errno to EINVAL. Otherwise, a four-byte value is
240 copied from the data buffer, updating the value of the
241 fpcr register.
242 /signal1, /signal2
244 The files provide access to the two signal notification channels
245 of an SPU. These are read-write files that operate on four-byte
246 words. Writing to one of these files triggers an interrupt on
247 the SPU. The value written to the signal files can be read from
248 the SPU through a channel read or from host user space through
249 the file. After the value has been read by the SPU, it is reset
250 to zero. The possible operations on an open signal1 or signal2
251 file are:
252 read(2)
254 If count is smaller than four, read(2) returns -1 and
255 sets errno to EINVAL. Otherwise, a four-byte value is
256 placed in the data buffer; this is the current value of
257 the specified signal notification register.
258 write(2)
260 If count is smaller than four, write(2) returns -1 and
261 sets errno to EINVAL. Otherwise, a four-byte value is
262 copied from the data buffer, updating the value of the
263 specified signal notification register. The signal noti‐
264 fication register will either be replaced with the input
265 data or will be updated to the bitwise OR operation of
266 the old value and the input data, depending on the con‐
267 tents of the signal1_type or signal2_type files respec‐
268 tively.
269 /signal1_type, /signal2_type
271 These two files change the behavior of the signal1 and signal2
272 notification files. They contain a numeric ASCII string which
273 is read as either "1" or "0". In mode 0 (overwrite), the hard‐
274 ware replaces the contents of the signal channel with the data
275 that is written to it. In mode 1 (logical OR), the hardware
276 accumulates the bits that are subsequently written to it. The
277 possible operations on an open signal1_type or signal2_type file
278 are:
279 read(2)
281 When the count supplied to the read(2) call is shorter
282 than the required length for the digit (plus a newline
283 character), subsequent reads from the same file descrip‐
284 tor will complete the string. When a complete string has
285 been read, all subsequent read operations will return
286 zero bytes and a new file descriptor needs to be opened
287 to read the value again.
288 write(2)
290 A write(2) operation on the file sets the register to the
291 value given in the string. The string is parsed from the
292 beginning until the first nonnumeric character or the end
293 of the buffer. Subsequent writes to the same file
294 descriptor overwrite the previous setting.
295 /mbox_info, /ibox_info, /wbox_info, /dma_into, /proxydma_info
297 Read-only files that contain the saved state of the SPU mail‐
298 boxes and DMA queues. This allows the SPU status to be
299 inspected, mainly for debugging. The mbox_info and ibox_info
300 files each contain the four-byte mailbox message that has been
301 written by the SPU. If no message has been written to these
302 mailboxes, then contents of these files is undefined. The
303 mbox_stat, ibox_stat and wbox_stat files contain the available
304 message count.
305 The wbox_info file contains an array of four-byte mailbox mes‐
307 sages, which have been sent to the SPU. With current CBEA
308 machines, the array is four items in length, so up to 4 * 4 = 16
309 bytes can be read from this file. If any mailbox queue entry is
310 empty, then the bytes read at the corresponding location are
311 undefined.
312 The dma_info file contains the contents of the SPU MFC DMA
314 queue, represented as the following structure:
315 struct spu_dma_info {
317 uint64_t dma_info_type;
318 uint64_t dma_info_mask;
319 uint64_t dma_info_status;
320 uint64_t dma_info_stall_and_notify;
321 uint64_t dma_info_atomic_command_status;
322 struct mfc_cq_sr dma_info_command_data[16];
323 };
324 The last member of this data structure is the actual DMA queue,
326 containing 16 entries. The mfc_cq_sr structure is defined as:
327 struct mfc_cq_sr {
329 uint64_t mfc_cq_data0_RW;
330 uint64_t mfc_cq_data1_RW;
331 uint64_t mfc_cq_data2_RW;
332 uint64_t mfc_cq_data3_RW;
333 };
334 The proxydma_info file contains similar information, but
336 describes the proxy DMA queue (i.e., DMAs initiated by entities
337 outside the SPU) instead. The file is in the following format:
338 struct spu_proxydma_info {
340 uint64_t proxydma_info_type;
341 uint64_t proxydma_info_mask;
342 uint64_t proxydma_info_status;
343 struct mfc_cq_sr proxydma_info_command_data[8];
344 };
345 Accessing these files requires that the SPU context is scheduled
347 out - frequent use can be inefficient. These files should not
348 be used for normal program operation.
349 These files are not present on contexts that have been created
351 with the SPU_CREATE_NOSCHED flag.
352 /cntl This file provides access to the SPU Run Control and SPU status
354 registers, as an ASCII string. The following operations are
355 supported:
356 read(2)
358 Reads from the cntl file will return an ASCII string with
359 the hex value of the SPU Status register.
360 write(2)
362 Writes to the cntl file will set the context's SPU Run
363 Control register.
364 /mfc Provides access to the Memory Flow Controller of the SPU. Read‐
366 ing from the file returns the contents of the SPU's MFC Tag Sta‐
367 tus register, and writing to the file initiates a DMA from the
368 MFC. The following operations are supported:
369 write(2)
371 Writes to this file need to be in the format of a MFC DMA
372 command, defined as follows:
373 struct mfc_dma_command {
375 int32_t pad; /* reserved */
376 uint32_t lsa; /* local storage address */
377 uint64_t ea; /* effective address */
378 uint16_t size; /* transfer size */
379 uint16_t tag; /* command tag */
380 uint16_t class; /* class ID */
381 uint16_t cmd; /* command opcode */
382 };
383 Writes are required to be exactly sizeof(struct
385 mfc_dma_command) bytes in size. The command will be sent
386 to the SPU's MFC proxy queue, and the tag stored in the
387 kernel (see below).
388 read(2)
390 Reads the contents of the tag status register. If the
391 file is opened in blocking mode (i.e., without O_NON‐
392 BLOCK), then the read will block until a DMA tag (as per‐
393 formed by a previous write) is complete. In nonblocking
394 mode, the MFC tag status register will be returned with‐
395 out waiting.
396 poll(2)
398 Calling poll(2) on the mfc file will block until a new
399 DMA can be started (by checking for POLLOUT) or until a
400 previously started DMA (by checking for POLLIN) has been
401 completed.
402 /mss Provides access to the MFC MultiSource Synchroniza‐
404 tion (MSS) facility. By mmap(2)-ing this file, processes
405 can access the MSS area of the SPU.
406 The following operations are supported:
408 mmap(2)
410 Mapping mss into the process address space gives access
411 to the SPU MSS area within the process address space.
412 Only MAP_SHARED mappings are allowed.
413 /psmap Provides access to the whole problem-state mapping of the SPU.
415 Applications can use this area to interface to the SPU, rather
416 than writing to individual register files in spufs.
417 The following operations are supported:
419 mmap(2)
421 Mapping psmap gives a process a direct map of the SPU
422 problem state area. Only MAP_SHARED mappings are sup‐
423 ported.
424 /phys-id
426 Read-only file containing the physical SPU number that the SPU
427 context is running on. When the context is not running, this
428 file contains the string "-1".
429 The physical SPU number is given by an ASCII hex string.
431 /object-id
433 Allows applications to store (or retrieve) a single 64-bit ID
434 into the context. This ID is later used by profiling tools to
435 uniquely identify the context.
436 write(2)
438 By writing an ASCII hex value into this file, applica‐
439 tions can set the object ID of the SPU context. Any pre‐
440 vious value of the object ID is overwritten.
441 read(2)
443 Reading this file gives an ASCII hex string representing
444 the object ID for this SPU context.
445
447 /etc/fstab entry
448 none /spu spufs gid=spu 0 0
449
451 close(2), spu_create(2), spu_run(2), capabilities(7)
452 The Cell Broadband Engine Architecture (CBEA) specification
454
456 This page is part of release 3.53 of the Linux man-pages project. A
457 description of the project, and information about reporting bugs, can
458 be found at http://www.kernel.org/doc/man-pages/.
459Linux 2007-12-20 SPUFS(7)