spu_run - execute an SPU context

#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).

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.

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.

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);
}

close(2), spu_create(2), capabilities(7), spufs(7)