setLED.S

# SPDX-License-Identifier: Unlicense
# Copyright (c) 2018 Western Digital Corporation or its affiliates.

.section .text
.align 2
.globl setLED

.include "memory_map.inc"
.include "gpio.inc"

.equ NOERROR,   0x00
.equ ERROR,     0x01
.equ LEDON,     0x01

# Selected LED to set comes in register a0
# Desired On/Off state comes in register a1

setLED:
    addi sp, sp, -16            # Allocate Stack Frame
    sw ra, 12(sp)               # Save the return address onto the stack

    li t0, GPIO_CTRL_ADDR       # Load the base GPIO address
    lw t1, GPIO_OUTPUT_VAL(t0)  # Get the current value of the pins

    beqz a1, ledOff             # Branch to ledOff if the request is to turn off LED
    li t2, LEDON                # Load On/1 to compare if that's what was requested
    beq a1, t2, ledOn           # Branch to ledOn if that's what was requested
    li a0, ERROR                # If we get here, we have a bogus request, return error
    j exit

ledOn:
    xor t1, t1, a0              # Do an XOR to only change the the value of the requested LED
    sw t1, GPIO_OUTPUT_VAL(t0)  # Write the new output so we turn on the requested LED
    li a0, NOERROR              # Return no error
    j exit

ledOff:
    xor a0, a0, 0xffffffff      # Invert everything so all bits are one except the requested bit
    and t1, t1, a0              # Add the values to only turn off the requested bit
    sw t1, GPIO_OUTPUT_VAL(t0)  # Write the new value to turn off the requested LED
    li a0, NOERROR              # Return no error

exit:
    lw ra, 12(sp)               # Restore the return address
    addi sp, sp, 16             # Deallocate stack frame
    ret