STM32WL55 - ADC conversion time

[MichaelMor]

Hello everyone!

I'm working on STM32WL55JCI7 board and trying to run ADC at the fastest speed (min total conversion time mention on datasheet 0.4uSec) and I don't receive this time.

My configuration is the following:

And to measure total time of conversion I'm using GPIO as RT check like the following:

//Turn GPIO on 

HAL_GPIO_WritePin(GPIOC, GPIO_PIN_4, GPIO_PIN_SET);

 

// Start ADC conversion, function reutrn

HAL_ADC_Start(&hadc);

 

    /* Wait till conversion is done */

while(LL_ADC_REG_IsConversionOngoing(hadc.Instance) == 0UL);

 

//Turn GPIO off

HAL_GPIO_WritePin(GPIOC, GPIO_PIN_4, GPIO_PIN_RESET);

 

Result (via scope) is 2.1uSec total time.

Also my optimization of C/C++ builder setting is optimize for speed.
Any advice how to run ADC at maximum speed?

BTW, when trying to change to Sync clock divide by 1 getting the following error:

I'll appreciate your help!

Thanks!

[AScha.3]

just to do a correct time measurement : put in a set/reset pin without adc() , to see how much time hal functions need.

like this:

//Turn GPIO on 
HAL_GPIO_WritePin(GPIOC, GPIO_PIN_4, GPIO_PIN_SET);
 
//Turn GPIO off
HAL_GPIO_WritePin(GPIOC, GPIO_PIN_4, GPIO_PIN_RESET);

 

the adc conv.time is the time(adc+pin set)  - time(pin set) .

[MichaelMor]

But does the way I measured ADC runtime is fine? there is a better/accurate way? like system clock cycles?
I tried, so with ADC I got the following result (GPIO4 connected to scope -1.287uSec)

 

and with only set/reset command give me (343nSec):

 

So I got 1287 - 343 = ~900nSec = 0.9uSec, still twice then datasheet
How can I reduce it?

[AScha.3]

>But does the way I measured ADC runtime is fine?

basically - yes. but your ADC-conv.time is including the HAL call time, going sub...return, and the wait-ready-loop, also need some time, to check for adc ready.

so to see the adc-time alone , you should start adc by register access, if possible.

(i did this way: first convert by HAL call; now adc is set ready to run, hal did it. then write to AD_CR -> ADEN bit 1...

try...

>How can I reduce it?

direct register access; but "pure" adc speed you can get only by using DMA to put result to an array, without any cpu start and check ready loops; and simply adc in continuous mode, so running as fast, as it can be.