source: soft/giet_vm/libs/libsrl/srl_lock.c @ 163

#include "srl_lock.h"

int srl_lock_lock(srl_lock_t slock )
{
   register int delay= rand();

    asm volatile ("_locks_llsc:                         \n"
                  "ll   $2,    0(%0)                \n" // $2 <= _locks_lock
                  "bnez $2,    _locks_delay         \n" // random delay if busy
                  "li   $3,    1                            \n" // prepare argument for sc  
                  "sc   $3,    0(%0)                \n" // try to set _locks_busy
                  "bnez $3,    _locks_ok        \n" // exit if atomic 
                  "_locks_delay:                                \n"
                  "move $4,    %1                           \n" // $4 <= delay
                  "_locks_loop:                             \n"
                  "addi $4,    $4,    -1            \n" // $4 <= $4 - 1
                  "beqz $4,    _locks_loop          \n" // test end delay
                  "j           _locks_llsc      \n"     // retry
                  "_locks_ok:                               \n"
                  ::"r"(&(slock.lock)),"r"(delay):"$2","$3","$4");
    return 0;
}

void srl_lock_unlock( srl_lock_t slock )
{
        asm volatile( "sw $0,   (%0)\n"
                                  "sync                   "
                                  ::"r"(&(slock.lock)));
}

int srl_lock_try_lock( srl_lock_t slock )
{
        register int ret = 0;   
        asm volatile ("ll   $2,    0(%1)                    \n" // $2 <= _locks_lock
                  "bnez $2,    _lock_done           \n" // exitif busy
                  "li   $3,    1                            \n" // prepare argument for sc  
                  "sc   $3,    0(%1)                \n" // try to set _locks_busy
                  "add  %0, $0, $3                  \n" // ret(exit) value
                  "_lock_done:                          \n"
                  :"=r"(ret)
                  :"r"(&(slock.lock))
                  :"$2","$3");
    return ret;
}