PSP Hello World callback.s Assembly

.data
    callback_exitRequest:   .word   1
    callback_sceKernelCreateCallback_001:   .asciiz "Exit Callback"
    callback_sceKernelCreateThread_001:     .asciiz "Callback Update Thread"

.text
    .globl  isRunning
    .type isRunning, @function
isRunning:
    la $t0, callback_exitRequest
    lw $v0, ($t0)
    jr $ra
    nop


    .globl  exitCallback
    .type exitCallback, @function
exitCallback:
    la $t0, callback_exitRequest
    li $t1, 0
    sw $t1, ($t0)
    li $v0, 0
    jr $ra
    nop


    .globl  callbackThread
    .type callbackThread, @function
callbackThread:
    addiu $sp, $sp, -4      # retain ra
    sw $ra, ($sp)

    la $t0, callback_sceKernelCreateCallback_001
    lw $a0, ($t0)
    la $t0, exitCallback
    lw $a1, ($t0)
    li $a2, 0
    jal sceKernelCreateCallback
    nop
    move $a0, $v0
    jal sceKernelRegisterExitCallback
    nop
    jal sceKernelSleepThreadCB
    nop

    lw $ra, ($sp)           # pop $ra from stack
    addiu $sp, $sp, 4
    jr $ra
    nop


    .globl  setupExitCallback
    .type setupExitCallback, @function
setupExitCallback:
    addiu $sp, $sp, -4      # retain ra
    sw $ra, ($sp)

    la $t0, callback_sceKernelCreateThread_001
    lw $a0, ($t0)
    la $t0, callbackThread
    lw $a1, ($t0)
    li $a2, 0x11
    li $a3, 0xFA0
    li $t0, 0x80000000
    li $t1, 0
    sw $t0, 16($fp)
    sw $t1, 20($fp)
    jal sceKernelCreateThread   # have to load some variables to stack
    nop

    blez $v0, .nullptrts
    move $a0, $v0
    jal sceKernelStartThread
    nop
.nullptrts:
    lw $ra, ($sp)           # pop $ra from stack
    addiu $sp, $sp, 4
    jr $ra
    nop