NAME

spu_run - execute an SPU context

LIBRARY

Standard C library (libc, -lc)

SYNOPSIS

#include <sys/spu.h>          /* Definition of SPU_* constants */
#include <sys/syscall.h>      /* Definition of SYS_* constants */
#include <unistd.h>

int syscall(SYS_spu_run, int fd, uint32_t *npc, uint32_t *event);

Note: glibc provides no wrapper for spu_run(), necessitating the use of syscall(2).

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 failure, it returns -1 and sets errno is set to indicate the error.

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.

STANDARDS

Linux on PowerPC.

HISTORY

Linux 2.6.16.

NOTES

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 http://www.bsc.es/projects/deepcomputing/linuxoncell/ 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 <err.h>
#include <fcntl.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
int main(void)
{
    int       context, fd, spu_status;
    uint32_t  instruction, npc;
    context = syscall(SYS_spu_create, "/spu/example-context", 0, 0755);
    if (context == -1)
        err(EXIT_FAILURE, "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)
        err(EXIT_FAILURE, "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 = syscall(SYS_spu_run, context, &npc, NULL);
    if (spu_status == -1)
        err(EXIT_FAILURE, "open");
    /*
     * We should see a status code of 0x12340002:
     *   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);
}