.syntax unified
.global main

//Ass-1-P-2

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ the audio framework has two functions:
@
@ 1. init_audio (call this once at the start of your program)
@
@ 2. play audio_sample (sends the low 16 bits of r0 out the
@    headphone jack - call this repeatedly in your main loop)
@
@ the rest is up to you!
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

main:
	@ your code goes here

	bl init_audio	//Init Audio, self explanatory

	mov r0, #0 		//Init the register to 0. This is possibly uneccesary

	mov r8, #0 		//Our future loop counter for the period, init here
	mov r9, #0 		//Our Ascending/Descending boolean flag, starting at 0, for ascend

	mov r10, #480 	//Upper (technically lower) limit. Interchangeable, results may be less interesting.
	mov r11, #48	//Lower (technically upper) limit.
	mov r12, #218 	//Our current frequency register, starting at 218 (440Hz on 192kHZ Board/2)

@@@@@@@@@@@@@--TOP WAVE--@@@@@@@@@@@@@@@@@@@@@@@@

init_top:
	mov r8, #0 //Reset period counter

play_top:
	cmp r8, r12						//If counter has surpassed Frequency in R2 (Hz/2) return 0
	beq init_bottom 				//If 0 returned, move to bottom wave
	mov r0, 0x00006000 				//Amplitude of the Wave
	adds r8, #1 					//Increment period counter
	bl play_audio_sample 			//Play
	b play_top						//Repeat

@@@@@@@@@@@@@@@--BOTTOM WAVE--@@@@@@@@@@@@@@@@@@

init_bottom:
	mov r8, #0 //Reset Period counter

play_bottom:
	cmp r8, r12						//If counter has surpassed Frequency in R2 (Hz/2) return 0
	beq modify_sound				//If 0 returned, move to modifying the signal
	mov r0, 0x0000A000 				//Inverse of 4000 from Top
	adds r8, #1 					//Increment period counter
	bl play_audio_sample 			//Play
	b play_bottom 					//Repeat

@@@@@@@@@@@@@@@--Handle Changes--@@@@@@@@@@@@@@@@@@

modify_sound:
	cmp r12, r10					//Compare Frequency with defind upper limit
	beq set_ascend					//If it's at the upper limit, begin ascent
	cmp r12, r11					//If at bottom limit
	beq set_descend					//then begin descent
return_point:						//Return here from toggling flag
	cmp r9, #0						//Check flag
	beq descend						//Jump to descend when 0
	b ascend						//Otherwise jump to ascend

set_ascend:
	mov r9, #0						//Set Flag to Ascend
	b return_point					//Return to Execution

set_descend:
	mov r9, #1						//Set Flag to Descend
	b return_point					//Return to Execution

ascend:
	adds r12, #2					//Add to the Frequency counter
	b repeat						//Jump to the loop point

descend:
	subs r12, #2					//Subtracts from the Frequency counter
	b repeat						//Jump to the loop point

repeat:
	b init_top						//Return to top and begin again

end:
	nop								//This is probably not needed, but there for redundancy