ULP ADC read help

[bonadio]

Hello

I have a running app reading the ADC channel while sleeping and the channel is set fixed in the code

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.set adc_channel, 5

adc r1, 0, adc_channel + 1

This code works, but now I need to pass the channel dynamically

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;.set adc_channel, 5

	.global adc_channel
adc_channel:
	.long 0 

adc r1, 0, adc_channel + 1
	

I comment the .set and created a variable called ulp_adc_channel and set it on the c code but this does not work.

What would be the correct way to set the channel dynamically?

I tried the following code too but did not worked

Code: Select all

	.global adc_channel
adc_channel:
	.long 0 

move r2, adc_channel
adc r1, 0, r2
	

This is the full code

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#include "soc/rtc_cntl_reg.h"
#include "soc/soc_ulp.h"

	/* ADC1 channel 6, GPIO34 */
	
	; .set adc_channel, 4 

	/* Configure the number of ADC samples to average on each measurement.
	   For convenience, make it a power of 2. */
	.set adc_oversampling_factor_log, 2
	.set adc_oversampling_factor, (1 << adc_oversampling_factor_log)

	/* Define variables, which go into .bss section (zero-initialized data) */
	.bss


	.global adc_channel
adc_channel:
	.long 0 

	.global last_result
last_result:
	.long 0

	/* Code goes into .text section */
	.text
	.global entry
entry:
	/* do measurements using ADC */
	/* r0 will be used as accumulator */
	move r0, 0
	/* initialize the loop counter */
	stage_rst
measure:
	/* measure and add value to accumulator */
	; adc r1, 0, adc_channel + 1
	move r2, adc_channel 
	adc r1, 0, r2
	add r0, r0, r1
	/* increment loop counter and check exit condition */
	stage_inc 1
	jumps measure, adc_oversampling_factor, lt

	/* divide accumulator by adc_oversampling_factor.
	   Since it is chosen as a power of two, use right shift */
	rsh r0, r0, adc_oversampling_factor_log
	/* averaged value is now in r0; store it into last_result */
	move r3, last_result
	st r0, r3, 0
	halt

Thanks

[boarchuz]

Not directly possible.
You'll either need to include all variations of ADC instruction in the ULP program and have the ULP jump to the correct one based on a variable that can be changed by the SoC, or change the ULP program when you want to change the ADC channel.

You could try updating just the one instruction, eg.

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#define ULP_PROG_ADC_INSN_OFFSET 7
static void update_ulp_adc(uint8_t adc_index, uint8_t channel) {
    ulp_insn_t *adc_insn = (ulp_insn_t *)RTC_SLOW_MEM + ULP_PROG_ADC_INSN_OFFSET;
    assert(adc_insn->adc.opcode == OPCODE_ADC && "not adc instruction");
    
    ulp_insn_t new_instruction = I_ADC(adc_insn->adc.dreg, adc_index, channel);
    *adc_insn = new_instruction;
}

update_ulp_adc(0, 1); // gpio 37
update_ulp_adc(1, 9); // gpio 26

You will need to handle the possibility of a conflict.

[bonadio]

Hi @boarchuz

Thanks for the response, I will go with jump inside the ULP based on a variable

[]s