--------------- LED BLINK PROGRAM ---------------
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--- Do NOT use this file as the source assembly, as this format of comments are
--- not allowed in either assemblers (ours, or the official ARM assembler).
--- Please read README.md before reading this file
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--- How it works ---
-- In psuedocode, the overall idea:
--
--    setup()   
--    while (true):
--       turn_on()
--       sleep()
--       turn_off()
--       sleep()
--
-- Now, there is no sleep function obviously. So, we will use a loop to simulate
-- to simulate the sleep function. The loop will run for about 3 million times.
-- this was experimentally determined to be a good value for a sleep of about half a second.
-- In other words:
-- 
--    sleep(): for i=0 to 3,145,728: continue
--
-- We now start with the actual code.
--
--
-- The setup() part:
--
movz w1, #0x10              -- w1 contains the binary value 1 0000, this is to set the GPSET0 and GPCLR0 registers, to set/clear GPIO 4. 
movz w2, #0x1000            -- value to set the FSEL4 to output (001 followed by 000 four times). This is to set the GPIO 4 to output mode.
movz x3, #0x3f20, lsl #16   -- x3 contains the address of the GPIO registers.
str w2, [x3]                -- sets GPIO 2 to output mode (FSEL = 1).

-- This is the main while loop that will run forever.
loop:
str w1, [x3, #0x1c]         -- sets GPIO 2 on. GPSET0 address is [x3] + 0x1c. This writes 1 to the 4th bit of the GPSET0 register.
movz w4, #0x30, lsl #16     -- let i = 3,145,728. Used for the sleep function.

-- sleep() function:
sleep1:
subs w4, w4, #1             -- i--;
b.ne sleep1                 -- repeat until i = 0.

-- turn off the LED.
str w1, [x3, #0x28]         -- sets GPIO 2 off. GPCLR0 address is [x3] + 0x28. This writes 1 to the 4th bit of the GPCLR0 register.
movz w4, #0x30, lsl #16     -- let i = 3,145,728. Used for the sleep function.

-- sleep() function:
sleep2:
subs w4, w4, #1             -- i--;
b.ne sleep2                 -- repeat off.

b loop                      -- repeat the main loop