1 files changed, 46 insertions, 0 deletions
diff --git a/software/first/set_LED.S b/software/first/set_LED.S
new file mode 100644
index 0000000..e436615
--- /dev/null
+++ b/software/first/set_LED.S
@@ -0,0 +1,46 @@
+.section .text
+.align 2
+.global set_LED
+.include "memory_map.inc"
+.include "gpio.inc"
+
+.equ  NOERROR,  0x0
+.equ  ERROR,    0x1
+.equ  LEDON,    0x1
+
+# a0 contains LED to set, desired LED state in a1
+# a0 is also the return value...
+
+set_LED:
+	addi sp, sp, -16 # Allocate stack frame
+	sw ra, 12(sp)    # save return address to the stack
+
+	li t0, GPIO_CTRL_ADDR      # load base GPIO address 
+	lw t1, GPIO_OUTPUT_VAL(t0) # load state
+
+	beqz a1, ledOff   # branch if == 0
+	li t2, LEDON      # load up on val into t2
+
+	beq a1, t2, ledOn # branch if on requested
+	li  a0, ERROR     # bad status request, return error
+  j exit
+
+
+ledOn:
+  or t1, t1, a0               # only change the value of the requested LED (xor in the video)
+  sw t1, GPIO_OUTPUT_VAL(t0)  # write new LED values to the right address
+	li a0, NOERROR              # success
+  j exit
+
+
+ledOff:
+  xor a0, a0, 0xffffffff       # invert bits so off bits are off
+  and t1, t1, a0               # turn of LEDs
+  sw t1, GPIO_OUTPUT_VAL(t0)   # write new LED values to the right address
+	li  a0, NOERROR              # success
+
+
+exit:
+  lw ra, 12(sp)   # load return address
+  addi sp, sp, 16 # deallocate stack frame
+	ret