How to change stm32 m4 adc channel?

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Ed Lee

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Apr 26, 2021, 1:25:24 PMApr 26
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Does anyone know how to do it in register level?

I see many code examples using:

ADC_ChannelConfTypeDef sConfig = {ADC_CHANNEL_0, 1, ADC_SAMPLETIME_28CYCLES};
HAL_ADC_ConfigChannel(&hadc1, &sConfig);
or
ADC_RegularChannelConfig(ADC1, ADC_channel_0, 1, ADC_SampleTime_480Cycles);

but i don't have access to these routines from arm-gcc.

By the way, i am using this to read the adc data:

#include "stm32f407xx.h"
ADC1->CR2 |= ADC_CR2_SWSTART; // Start A2D
while (!(ADC1->SR & ADC_SR_EOC)); // ready wait
data = ADC1->DR;

David Brown

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Apr 27, 2021, 3:33:50 AMApr 27
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On 26/04/2021 19:25, Ed Lee wrote:
> Does anyone know how to do it in register level?
>
> I see many code examples using:
>
> ADC_ChannelConfTypeDef sConfig = {ADC_CHANNEL_0, 1, ADC_SAMPLETIME_28CYCLES};
> HAL_ADC_ConfigChannel(&hadc1, &sConfig);
> or
> ADC_RegularChannelConfig(ADC1, ADC_channel_0, 1, ADC_SampleTime_480Cycles);
>
> but i don't have access to these routines from arm-gcc.
>

That last statement shows you perhaps don't have a full understanding of
what you are doing here.

However, the most likely cause of your troubles is that the examples you
have are using an SDK from ST, and you either don't have the SDK
installed and set up correctly, or you aren't using it in your project,
or you have simply forgotten to include the appropriate headers at the
start of your C file.

I have not used ST's tools myself, but I would expect that their SDK
comes with complete working example projects for some evaluation boards.
Start with one of these, and adapt it to suit your required changes.

Michael Kellett

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Apr 27, 2021, 8:35:04 AMApr 27
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If you download and install ST's Cube etc you will end up with (amongst
a LOT of other stuff) the library code that you could use if you want
functions like:

HAL_ADC_ConfigChannel()

I don't use these - they try to be universal but end up being hard to
understand and slow.

To drive the ADC directly you will need to study the reference manual
and register descriptions and it may well help to look at some ST
examples (from the Cube again).

To address your specific problem:

Assuming a single conversion of one channel and starting after a
hardware reset:

write the channel to be converted into the SQ1 field of ADC_SQR3

make sure the L field of ADC_SQR1 = 0 so the ADC does just one conversion

set the SMP field for the channel in question to the sampling time you
want (ADC_SMPR1 or ADC_SMPR2)

enable the ADC by setting bit 0 in ADC_CR1

start the conversion by setting bit 30 in ADC_CR2

(All the above based on Ref manual for STM446xx - check details for your
own processor.)

You will need to enable the ADC clock but you must have got there already.

MK


Ed Lee

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Apr 27, 2021, 11:39:06 AMApr 27
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OK, i think this is getting close, but also need to select the Alt-Funct Reg for the port pin. I was hoping to find a complete example of such.

Michael Kellett

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Apr 27, 2021, 12:33:12 PMApr 27
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You don't use the GPIO port Alt Function Register for making a pin an
analogue input.
You do it by setting the mode bits for that pin in the GPIO Mode register.
There are two bits for each pin, coded like this:

Bits 2y:2y+1 MODERy[1:0]: Port x configuration bits (y = 0..15)
These bits are written by software to configure the I/O direction mode.
00: Input (reset state)
01: General purpose output mode
10: Alternate function mode
11: Analog mode

I don't have any shareable examples that don't use DMA with scan and
usually continuous mode for the ADC which I think might be distracting.

MK

Ed Lee

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Apr 27, 2021, 4:50:46 PMApr 27
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So, reading from PA0 or PA1 like this?

RCC->APB2ENR |= RCC_APB2ENR_ADC1EN; // Enable ADC clock
ADC1->CR2 |= ADC_CR2_ADON; // Enable ADC
ADC1->SQR1 = 0; // bit 23-20 single coversion
ADC->SMPR2 = 2; // 28 cycles

#if PA0
GPIOA->MODER |= 3; // bit 1-0 Analog mode
ADC1->SQR3 = 0; // bit 3-0,0 channel 0
#endif

#if PA1
GPIOA->MODER |= 0xc; // bit 3-2 Analog mode
ADC1->SQR3 = 1; // bit 3-0,0 channel 1
#endif

ADC1->CR2 |= ADC_CR2_SWSTART; // Start ADC
while (!(ADC1->SR & ADC_SR_EOC)); // ready wait
DATA = ADC1->DR; // read data

Michael Kellett

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Apr 28, 2021, 4:17:13 AMApr 28
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Not quite, entries in SMPR1/2 are for each ADC channel, not each entry
in the sequencer.
So for PA1 you need to set SMP1 bit field to 2,
ADC->SMPR2 = (uint32_t)2 << 3;

Here's a little challenge for you - good practice is to test this code
- and that would mean you should test that the sampling time is actually
what you meant it to be (not that you wrote x bits to y register).
How would you do that ?



MK

Ed Lee

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Apr 28, 2021, 10:17:10 AMApr 28
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OK, thanks.

> Here's a little challenge for you - good practice is to test this code
> - and that would mean you should test that the sampling time is actually
> what you meant it to be (not that you wrote x bits to y register).
> How would you do that ?

I guess i can measure the average conversion time from a sampling loop. For 100MHz clock, even 480 cycles are more than enough.

One question remain. How does it ties PA0 with channel 0? If it's hard coded, does it mean only port A can be analog?

Richard Damon

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Apr 28, 2021, 7:41:06 PMApr 28
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Each analog channel is hard tied internally to a given pin. (They are
all port A from my memory, but scattered about a bit). Read the device
reference manual for a listing of the capability of each pin.

Ed Lee

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Apr 28, 2021, 9:36:13 PMApr 28
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OK, i will have dig a bit deeper in the reference manual.

This info is critical for someone like me new to the STM chip.

For the (microchip/Atmel) μA SAM world, we have to set them explicitly.

PORT->Group[1].DIRCLR.reg = PORT_PB09;
// Enable the peripheral multiplexer for PB09
PORT->Group[1].PINCFG[9].reg |= PORT_PINCFG_PMUXEN;
// Set PB09 to function B which is analog input.
PORT->Group[1].PMUX[4].reg = PORT_PMUX_PMUXO_B;

Richard Damon

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Apr 28, 2021, 10:48:32 PMApr 28
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The STM pins also have config registers to configure which special
function (if any) they are set for. There generally is a table listing
every pin and what functions it can connect to.
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