Open Music Labs Forums

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UP/DOWN SWEEP 18b - for the MICrODEC
Text based flow chart
last edited by: mcanulty  - Sept.28.2010
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variables:

	bit direction flag

	int left in 
		left LSB in
		left MSB in

	int left out
		left LSB out
		left MSB out

	int right in
		right LSB in
		right MSB in

	int right out
		right LSB out
		right MSB out

	18b read pointer
		read pntr LSB
		read pntr MSB
		read pntr HIGH
		
	18b write pointer
		read pntr LSB
		read pntr MSB
		read pntr HIGH
		
	18b read offset vector
		offset LSB
		offset MSB
		offset HIGH
		
	18b buffer size
		buff size LSB
		buff size MSB
		buff size HIGH
		
	int ADC value
		ADC val LSB
		ADC val MSB


START UP/DOWNSWEEP INTERRUPT ROUTINE


====  AUDIO XFER  =================================================================

-	out Left MSB
		
-	wait for SPI flag
	
-	in left MSB

-	out left LSB
	
-	request data from SRAM at read pointer (left/even)
		
-	increment read address (now points at right/odd)
		mask off unused bits
		set we bit
		
-	receive data from read pointer request 
		place in left channel out regs
		
-	wait for SPI flag
		
-	in left LSB

-	out right MSB

-	write left channel to SRAM at write pointer (left/even)
		set address lines to write pointer
		pull CE and WE low
		switch data lines direction to out
		load data lines
		pull we high
		switch data lines direction to in
		
-	wait for SPI flag

-	in right MSB

-	out right LSB

-	request data from SRAM at read pointer (right/odd)
		
-	increment write address (now points at right/odd)
		mask off unused bits
		
-	receive data from read pointer request 
		place in right channel out regs
	
-	wait for SPI flag

-	in right LSB

-	write right channel to SRAM at write pointer (right/odd)
		set address lines to write pointer
		pull CE and WE low
		switch data lines direction to out
		load data lines
		pull we high
		switch data lines direction to in
		
-	increment write address pointer (now points at left/even)

-	set read address equal to write address (in order to later subtract the offset)
		write pointer LSB  data -> read pointer LSB register 
		write pointer MSB  data -> read pointer MSB register
		write pointer HIGH data -> read pointer HIGH register
		
-	BRANCH TEST - Are we in forward mode?
		if yes, go to FORWARD MODE OFFSET UPDATE
		if no, go to REVERSE MODE OFFSET UPDATE
		
===================================================================================	
		
		
==== FORWARD MODE OFFSET UPDATE  ==================================================

-	decrease offset vector by 2  (read pointer plays forwards at 2x)

-	BRANCH TEST - Have we reached the beginning of the buffer, ie, offset equals 0?							  
		if yes, set offset to 4 and switch mode to reverse
		if no, proceed to CALCULATE READ ADDRESS 
		
===================================================================================	


==== REVERSE MODE OFFSET UPDATE  ==================================================

-	increase offset vector by 4  (read pointer plays backwards at 1x)

-	BRANCH TEST - Have we reached the bottom of the buffer, ie, offset >= buff size?
		if yes, reduce offset by 2 (replay last sample), switch mode to forward
		if no, proceed to CALCULATE READ ADDRESS 
		
===================================================================================	


==== CALCULATE READ ADDRESS  =======================================================

-	set read address pointer to write address pointer (already done)		

-	subtract offset from read address pointer

-	mask off unused bits in read pointer HIGH

-	set WE bit in read pointer HIGH

-	proceed to UPDATE BUFFER SIZE

===================================================================================	


====  UPDATE BUFFER SIZE  ===========================================================

-	place ADC Value in Buffer Size 
		ADC val LSB -> Buffer Size LSB
		ADC val MSB -> Buffer Size MSB
					0 -> Buffer Size HIGH
			
-	left shift Buffer Size two times (multiply by four) 

===================================================================================	


END UP/DOWNSWEEP INTERRUPT ROUTINE