1spufs(7) Miscellaneous Information Manual spufs(7)
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6 spufs - SPU filesystem
7
9 The SPU filesystem is used on PowerPC machines that implement the Cell
10 Broadband Engine Architecture in order to access Synergistic Processor
11 Units (SPUs).
12 The filesystem provides a name space similar to POSIX shared memory or
14 message queues. Users that have write permissions on the filesystem
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 filesystems. This list details the
38 supported operations and the deviations from the standard behavior de‐
39 scribed 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 op‐
68 erations 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 ac‐
78 cess to the SPU local storage within the process address
79 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 re‐
106 turned.
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 (un‐
112 less 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—that is, 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 re‐
165 turn a big-endian binary integer number. The only possible op‐
166 eration 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) re‐
181 quire that the SPU context be scheduled out, so frequent access
182 to these files is not recommended for normal program operation.
183 The contents of these files are:
185 npc Next Program Counter - valid only when the SPU
187 is in a stopped state.
188 decr SPU Decrementer
190 decr_status Decrementer Status
192 spu_tag_mask MFC tag mask for SPU DMA
194 event_mask Event mask for SPU interrupts
196 event_status Number of SPU events pending (read-only)
198 srr0 Interrupt Return address register
200 lslr Local Store Limit Register
202 The possible operations on these files are:
204 read(2)
206 Reads the current register value. If the register value
207 is larger than the buffer passed to the read(2) system
208 call, subsequent reads will continue reading from the
209 same buffer, until the end of the buffer is reached.
210 When a complete string has been read, all subsequent read
212 operations will return zero bytes and a new file descrip‐
213 tor needs to be opened to read a new value.
214 write(2)
216 A write(2) operation on the file sets the register to the
217 value given in the string. The string is parsed from the
218 beginning until the first nonnumeric character or the end
219 of the buffer. Subsequent writes to the same file de‐
220 scriptor overwrite the previous setting.
221 Except for the npc file, these files are not present on
223 contexts that have been created with the SPU_CRE‐
224 ATE_NOSCHED flag.
225 /fpcr This file provides access to the Floating Point Status and Con‐
227 trol Register (fcpr) as a binary, four-byte file. The opera‐
228 tions on the fpcr file are:
229 read(2)
231 If count is smaller than four, read(2) returns -1 and
232 sets errno to EINVAL. Otherwise, a four-byte value is
233 placed in the data buffer; this is the current value of
234 the fpcr register.
235 write(2)
237 If count is smaller than four, write(2) returns -1 and
238 sets errno to EINVAL. Otherwise, a four-byte value is
239 copied from the data buffer, updating the value of the
240 fpcr register.
241 /signal1, /signal2
243 The files provide access to the two signal notification channels
244 of an SPU. These are read-write files that operate on four-byte
245 words. Writing to one of these files triggers an interrupt on
246 the SPU. The value written to the signal files can be read from
247 the SPU through a channel read or from host user space through
248 the file. After the value has been read by the SPU, it is reset
249 to zero. The possible operations on an open signal1 or signal2
250 file are:
251 read(2)
253 If count is smaller than four, read(2) returns -1 and
254 sets errno to EINVAL. Otherwise, a four-byte value is
255 placed in the data buffer; this is the current value of
256 the specified signal notification register.
257 write(2)
259 If count is smaller than four, write(2) returns -1 and
260 sets errno to EINVAL. Otherwise, a four-byte value is
261 copied from the data buffer, updating the value of the
262 specified signal notification register. The signal noti‐
263 fication register will either be replaced with the input
264 data or will be updated to the bitwise OR operation of
265 the old value and the input data, depending on the con‐
266 tents of the signal1_type or signal2_type files respec‐
267 tively.
268 /signal1_type, /signal2_type
270 These two files change the behavior of the signal1 and signal2
271 notification files. They contain a numeric ASCII string which
272 is read as either "1" or "0". In mode 0 (overwrite), the hard‐
273 ware replaces the contents of the signal channel with the data
274 that is written to it. In mode 1 (logical OR), the hardware ac‐
275 cumulates the bits that are subsequently written to it. The
276 possible operations on an open signal1_type or signal2_type file
277 are:
278 read(2)
280 When the count supplied to the read(2) call is shorter
281 than the required length for the digit (plus a newline
282 character), subsequent reads from the same file descrip‐
283 tor will complete the string. When a complete string has
284 been read, all subsequent read operations will return
285 zero bytes and a new file descriptor needs to be opened
286 to read the value again.
287 write(2)
289 A write(2) operation on the file sets the register to the
290 value given in the string. The string is parsed from the
291 beginning until the first nonnumeric character or the end
292 of the buffer. Subsequent writes to the same file de‐
293 scriptor overwrite the previous setting.
294 /mbox_info, /ibox_info, /wbox_info, /dma_into, /proxydma_info
296 Read-only files that contain the saved state of the SPU mail‐
297 boxes and DMA queues. This allows the SPU status to be in‐
298 spected, mainly for debugging. The mbox_info and ibox_info
299 files each contain the four-byte mailbox message that has been
300 written by the SPU. If no message has been written to these
301 mailboxes, then contents of these files is undefined. The
302 mbox_stat, ibox_stat, and wbox_stat files contain the available
303 message count.
304 The wbox_info file contains an array of four-byte mailbox mes‐
306 sages, which have been sent to the SPU. With current CBEA ma‐
307 chines, the array is four items in length, so up to 4 * 4 = 16
308 bytes can be read from this file. If any mailbox queue entry is
309 empty, then the bytes read at the corresponding location are un‐
310 defined.
311 The dma_info file contains the contents of the SPU MFC DMA
313 queue, represented as the following structure:
314 struct spu_dma_info {
316 uint64_t dma_info_type;
317 uint64_t dma_info_mask;
318 uint64_t dma_info_status;
319 uint64_t dma_info_stall_and_notify;
320 uint64_t dma_info_atomic_command_status;
321 struct mfc_cq_sr dma_info_command_data[16];
322 };
323 The last member of this data structure is the actual DMA queue,
325 containing 16 entries. The mfc_cq_sr structure is defined as:
326 struct mfc_cq_sr {
328 uint64_t mfc_cq_data0_RW;
329 uint64_t mfc_cq_data1_RW;
330 uint64_t mfc_cq_data2_RW;
331 uint64_t mfc_cq_data3_RW;
332 };
333 The proxydma_info file contains similar information, but de‐
335 scribes the proxy DMA queue (i.e., DMAs initiated by entities
336 outside the SPU) instead. The file is in the following format:
337 struct spu_proxydma_info {
339 uint64_t proxydma_info_type;
340 uint64_t proxydma_info_mask;
341 uint64_t proxydma_info_status;
342 struct mfc_cq_sr proxydma_info_command_data[8];
343 };
344 Accessing these files requires that the SPU context is scheduled
346 out - frequent use can be inefficient. These files should not
347 be used for normal program operation.
348 These files are not present on contexts that have been created
350 with the SPU_CREATE_NOSCHED flag.
351 /cntl This file provides access to the SPU Run Control and SPU status
353 registers, as an ASCII string. The following operations are
354 supported:
355 read(2)
357 Reads from the cntl file will return an ASCII string with
358 the hex value of the SPU Status register.
359 write(2)
361 Writes to the cntl file will set the context's SPU Run
362 Control register.
363 /mfc Provides access to the Memory Flow Controller of the SPU. Read‐
365 ing from the file returns the contents of the SPU's MFC Tag Sta‐
366 tus register, and writing to the file initiates a DMA from the
367 MFC. The following operations are supported:
368 write(2)
370 Writes to this file need to be in the format of a MFC DMA
371 command, defined as follows:
372 struct mfc_dma_command {
374 int32_t pad; /* reserved */
375 uint32_t lsa; /* local storage address */
376 uint64_t ea; /* effective address */
377 uint16_t size; /* transfer size */
378 uint16_t tag; /* command tag */
379 uint16_t class; /* class ID */
380 uint16_t cmd; /* command opcode */
381 };
382 Writes are required to be exactly sizeof(struct
384 mfc_dma_command) bytes in size. The command will be sent
385 to the SPU's MFC proxy queue, and the tag stored in the
386 kernel (see below).
387 read(2)
389 Reads the contents of the tag status register. If the
390 file is opened in blocking mode (i.e., without O_NON‐
391 BLOCK), then the read will block until a DMA tag (as per‐
392 formed by a previous write) is complete. In nonblocking
393 mode, the MFC tag status register will be returned with‐
394 out waiting.
395 poll(2)
397 Calling poll(2) on the mfc file will block until a new
398 DMA can be started (by checking for POLLOUT) or until a
399 previously started DMA (by checking for POLLIN) has been
400 completed.
401 /mss Provides access to the MFC MultiSource Synchroniza‐
403 tion (MSS) facility. By mmap(2)-ing this file, processes
404 can access the MSS area of the SPU.
405 The following operations are supported:
407 mmap(2)
409 Mapping mss into the process address space gives access
410 to the SPU MSS area within the process address space.
411 Only MAP_SHARED mappings are allowed.
412 /psmap Provides access to the whole problem-state mapping of the SPU.
414 Applications can use this area to interface to the SPU, rather
415 than writing to individual register files in spufs.
416 The following operations are supported:
418 mmap(2)
420 Mapping psmap gives a process a direct map of the SPU
421 problem state area. Only MAP_SHARED mappings are sup‐
422 ported.
423 /phys-id
425 Read-only file containing the physical SPU number that the SPU
426 context is running on. When the context is not running, this
427 file contains the string "-1".
428 The physical SPU number is given by an ASCII hex string.
430 /object-id
432 Allows applications to store (or retrieve) a single 64-bit ID
433 into the context. This ID is later used by profiling tools to
434 uniquely identify the context.
435 write(2)
437 By writing an ASCII hex value into this file, applica‐
438 tions can set the object ID of the SPU context. Any pre‐
439 vious value of the object ID is overwritten.
440 read(2)
442 Reading this file gives an ASCII hex string representing
443 the object ID for this SPU context.
444
446 To automatically mount(8) the SPU filesystem when booting, at the loca‐
447 tion /spu chosen by the user, put this line into the fstab(5) configu‐
448 ration file:
449 none /spu spufs gid=spu 0 0
450
452 close(2), spu_create(2), spu_run(2), capabilities(7)
453 The Cell Broadband Engine Architecture (CBEA) specification
455Linux man-pages 6.04 2023-02-05 spufs(7)