SPU_RUN

Section: Linux Programmer's Manual (2)
Updated: 2020-11-01
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NAME

spu_run - execute an SPU context

SYNOPSIS

#include <sys/spu.h>

int spu_run(int fd, unsigned int *npc, unsigned int *event);

Note: There is no glibc wrapper for this system call; see NOTES.

DESCRIPTION

The spu_run() system call is used on PowerPC machines that implement the Cell Broadband Engine Architecture in order to access Synergistic Processor Units (SPUs). The fd argument is a file descriptor returned by spu_create(2) that refers to a specific SPU context. When the context gets scheduled to a physical SPU, it starts execution at the instruction pointer passed in npc.

Execution of SPU code happens synchronously, meaning that spu_run() blocks while the SPU is still running. If there is a need to execute SPU code in parallel with other code on either the main CPU or other SPUs, a new thread of execution must be created first (e.g., using pthread_create(3)).

When spu_run() returns, the current value of the SPU program counter is written to npc, so successive calls to spu_run() can use the same npc pointer.

The event argument provides a buffer for an extended status code. If the SPU context was created with the SPU_CREATE_EVENTS_ENABLED flag, then this buffer is populated by the Linux kernel before spu_run() returns.

The status code may be one (or more) of the following constants:

SPE_EVENT_DMA_ALIGNMENT: A DMA alignment error occurred.
SPE_EVENT_INVALID_DMA: An invalid MFC DMA command was attempted.
SPE_EVENT_SPE_DATA_STORAGE: A DMA storage error occurred.
SPE_EVENT_SPE_ERROR: An illegal instruction was executed.

NULL is a valid value for the event argument. In this case, the events will not be reported to the calling process.

RETURN VALUE

On success, spu_run() returns the value of the spu_status register. On error, it returns -1 and sets errno to one of the error codes listed below.

The spu_status register value is a bit mask of status codes and optionally a 14-bit code returned from the stop-and-signal instruction on the SPU. The bit masks for the status codes are:

0x02: SPU was stopped by a stop-and-signal instruction.
0x04: SPU was stopped by a halt instruction.
0x08: SPU is waiting for a channel.
0x10: SPU is in single-step mode.
0x20: SPU has tried to execute an invalid instruction.
0x40: SPU has tried to access an invalid channel.
0x3fff0000: The bits masked with this value contain the code returned from a stop-and-signal instruction. These bits are valid only if the 0x02 bit is set.

If spu_run() has not returned an error, one or more bits among the lower eight ones are always set.

ERRORS

EBADF: fd is not a valid file descriptor.
EFAULT: npc is not a valid pointer, or event is non-NULL and an invalid pointer.
EINTR: A signal occurred while spu_run() was in progress; see signal(7). The npc value has been updated to the new program counter value if necessary.
EINVAL: fd is not a valid file descriptor returned from spu_create(2).
ENOMEM: There was not enough memory available to handle a page fault resulting from a Memory Flow Controller (MFC) direct memory access.
ENOSYS: The functionality is not provided by the current system, because either the hardware does not provide SPUs or the spufs module is not loaded.

VERSIONS

The spu_run() system call was added to Linux in kernel 2.6.16.

CONFORMING TO

This call is Linux-specific and implemented only by the PowerPC architecture. Programs using this system call are not portable.

NOTES

Glibc does not provide a wrapper for this system call; call it using syscall(2). Note however, that spu_run() is meant to be used from libraries that implement a more abstract interface to SPUs, not to be used from regular applications. See for the recommended libraries.

EXAMPLES

The following is an example of running a simple, one-instruction SPU program with the spu_run() system call.

#include <stdlib.h> #include <stdint.h> #include <unistd.h> #include <stdio.h> #include <sys/types.h> #include <fcntl.h>

#define handle_error(msg) \
do { perror(msg); exit(EXIT_FAILURE); } while (0)

int main(void) {
int context, fd, spu_status;
uint32_t instruction, npc;

    context = spu_create("/spu/example-context", 0, 0755);
    if (context == -1)
        handle_error("spu_create");

    /* write a 'stop 0x1234' instruction to the SPU's
     * local store memory
     */
    instruction = 0x00001234;

    fd = open("/spu/example-context/mem", O_RDWR);
    if (fd == -1)
        handle_error("open");
    write(fd, &instruction, sizeof(instruction));

    /* set npc to the starting instruction address of the
     * SPU program. Since we wrote the instruction at the
     * start of the mem file, the entry point will be 0x0
     */
    npc = 0;

    spu_status = spu_run(context, &npc, NULL);
    if (spu_status == -1)
        handle_error("open");

    /* we should see a status code of 0x1234002:
     *   0x00000002 (spu was stopped due to stop-and-signal)
     * | 0x12340000 (the stop-and-signal code)
     */
    printf("SPU Status: %#08x\n", spu_status);

exit(EXIT_SUCCESS); }

COLOPHON

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