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Finalize ADC related code and docs.

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This commit is contained in:
Renaud 2025-01-19 15:18:45 +08:00
parent e24be26c20
commit 2ecba6974b
6 changed files with 155 additions and 55 deletions
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3
Makefile
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@ -123,7 +123,8 @@ CRC32SIGN := 1
##SRCS = startup.txeie.c adc.c adccalib.c ds18b20.c
#SRCS = startup.ram.c txeie.c uptime.1.c
#SRCS = startup.crc.c txeie.c uptime.c
SRCS = startup.crc.c adc.c adcmain.c
#SRCS = startup.crc.c adc.c adcmain.c
SRCS = startup.crc.c adc.c adcext.c
LIBSRCS = printf.c putchar.c puts.c # memset.c memcpy.c
ALLSRCS = $(SRCS) $(LIBSRCS)

75
adc.c
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@ -1,5 +1,5 @@
/* adc.c -- system layer
** Copyright (c) 2020-2021 Renaud Fivet
** Copyright (c) 2020-2025 Renaud Fivet
**
** ADC for temperature sensor and Vrefint
** gpioa low level API and usleep()
@ -64,6 +64,8 @@
#define RCC_APB2ENR_USART1EN 0x00004000 /* 14: USART1 clock enable */
#define RCC_APB2ENR_ADCEN 0x00000200 /* 9: ADC clock enable */
#define RCC_CFGR2 RCC[ 11] /* 3-0: PLL PREDIV */
#define RCC_CR2 RCC[ 13]
#define RCC_CR2_HSI14ON 0x00000001 /* 1: HSI14 clock enable */
#define RCC_CR2_HSI14RDY 0x00000002 /* 2: HSI14 clock ready */
@ -126,15 +128,20 @@
#define LED_IOP A
#define LED_PIN 4
#define LED_ON 0
/* 8MHz quartz, configure PLL at 28MHz */
/* 8MHz quartz, configure PLL at 16MHz */
//#define HSE 8000000
#define PLL 7
//#define HSEPRE 4
#define PLL 6
#define BAUD 9600
//#define HSI14 1
#ifdef PLL
# ifdef HSE
# define CLOCK HSE / 2 * PLL
# ifdef HSEPRE
# define CLOCK HSE / HSEPRE * PLL
# else
# define CLOCK HSE / 2 * PLL
# endif
# else /* HSI */
# define CLOCK 8000000 / 2 * PLL
# endif
@ -151,6 +158,12 @@
# error clock frequency exceeds 48MHz
#endif
#if CLOCK > 0x1000000
# define TICKDIV 8
#else
# define TICKDIV 1
#endif
#if CLOCK % BAUD
# warning baud rate not accurate at that clock frequency
#endif
@ -225,13 +238,11 @@ void SysTick_Handler( void) {
}
void usleep( unsigned usecs) { /* wait at least usec µs */
#if CLOCK / 8000000 < 1
# error HCLK below 8 MHz
#elif CLOCK % 8000000
# warning HCLK is not multiple of 8 MHz
void usleep( unsigned usecs) { /* wait at least usecs µs */
#if CLOCK % (TICKDIV * 1000000)
# warning usleep() not accurate at that clock frequency
#endif
usecs = SYSTICK_CVR - (CLOCK / 8000000 * usecs) ;
usecs = SYSTICK_CVR - (CLOCK / TICKDIV / 1000000 * usecs) ;
while( SYSTICK_CVR > usecs) ;
}
@ -251,7 +262,7 @@ iolvl_t gpioa_read( int pin) { /* Read level of GPIOA pin */
}
static void adc_init( void) {
const unsigned short *adc_init( unsigned channels) {
/* Enable ADC peripheral */
RCC_APB2ENR |= RCC_APB2ENR_ADCEN ;
/* Setup ADC sampling clock */
@ -260,10 +271,11 @@ static void adc_init( void) {
do {} while( !( RCC_CR2 & RCC_CR2_HSI14RDY)) ; /* Wait for stable clock */
/* Select HSI14 as sampling clock for ADC */
// ADC_CFGR2 &= ~ADC_CFGR2_CKMODE ; /* Default 00 == HSI14 */
#else
#elif CLOCK <= 28000000
/* Select PCLK/2 as sampling clock for ADC */
ADC_CFGR2 |= ADC_CFGR2_PCLK2 ; /* 01 PCLK/2 Over default 00 */
// ADC_CFGR2 |= ADC_CFGR2_PCLK4 ; /* 10 PCLK/4 Over default 00 */
#else
ADC_CFGR2 |= ADC_CFGR2_PCLK4 ; /* 10 PCLK/4 Over default 00 */
#endif
/* Calibration */
@ -276,15 +288,20 @@ static void adc_init( void) {
} while( !( ADC_ISR & ADC_ISR_ADRDY)) ;
/* Select inputs, precision and scan direction */
ADC_CHSELR = 3 << 16 ; /* Channel 16: temperature, Channel 17: Vrefint */
ADC_SMPR = 7 ;
ADC_CCR |= ADC_CCR_TSEN | ADC_CCR_VREFEN ;
ADC_CHSELR = channels ;
ADC_SMPR = 7 ; /* 7 is 239.5 ADC clock cycles */
ADC_CCR |= (channels & (1 << 17)) << 5 ; /* VREFEN */
ADC_CCR |= (channels & (1 << 16)) << 7 ; /* TSEN */
/* Default scan direction (00) is Temperature before Voltage */
// ADC_CFGR1 &= ~ADC_CFGR1_SCANDIR ; /* Default 0 is low to high */
ADC_CFGR1 |= ADC_CFGR1_SCANDIR ; /* high to low */
ADC_CFGR1 |= ADC_CFGR1_DISCEN ; /* Enable Discontinuous mode */
return TS_CAL1 ;
}
static unsigned adc_convert( void) {
unsigned adc_convert( void) {
/* Either only one channel in sequence or Discontinuous mode ON */
ADC_CR |= ADC_CR_ADSTART ; /* Start ADC conversion */
do {} while( ADC_CR & ADC_CR_ADSTART) ; /* Wait for start command cleared */
@ -293,7 +310,7 @@ static unsigned adc_convert( void) {
void adc_vnt( vnt_cmd_t cmd, short *ptrV, short *ptrC) {
if( cmd == VNT_INIT)
adc_init() ;
adc_init( 3 << 16) ;
if( cmd <= VNT_CAL) {
/* Calibration Values */
@ -303,11 +320,11 @@ void adc_vnt( vnt_cmd_t cmd, short *ptrV, short *ptrC) {
}
/* ADC Conversion */
*ptrC = adc_convert() ;
*ptrV = adc_convert() ;
*ptrC = adc_convert() ;
if( cmd == VNT_VNC) {
*ptrC = 300 + (*TS_CAL1 - *ptrC * *VREFINT_CAL / *ptrV) * 10000 / 5336 ;
*ptrC = 300 + (*TS_CAL1 - *ptrC * *VREFINT_CAL / *ptrV) * 10000 / 5336 ;
*ptrV = 330 * *VREFINT_CAL / *ptrV ;
}
}
@ -326,11 +343,15 @@ int init( void) {
#ifdef PLL
/* Setup PLL HSx/2 * 6 [24MHz] */
/* Default 0: PLL HSI/2 src, PLL MULL * 2 */
RCC_CFGR =
# ifdef HSE
RCC_CFGR_PLLSRC_HSE | RCC_CFGR_PLLXTPRE_DIV2 |
# endif
RCC_CFGR = RCC_CFGR_PLLSRC_HSE | RCC_CFGR_PLLXTPRE_DIV2 |
RCC_CFGR_PLLMUL( PLL) ;
# ifdef HSEPRE
RCC_CFGR2 = HSEPRE - 1 ;
# endif
# else
RCC_CFGR = RCC_CFGR_PLLMUL( PLL) ;
# endif
RCC_CR |= RCC_CR_PLLON ;
do {} while( (RCC_CR & RCC_CR_PLLRDY) == 0) ; /* Wait for PLL */
@ -349,9 +370,13 @@ int init( void) {
#endif
/* SYSTICK */
SYSTICK_RVR = CLOCK / 8 - 1 ; /* HBA / 8 */
SYSTICK_RVR = CLOCK / TICKDIV - 1 ; /* HCLK / [8,1] */
SYSTICK_CVR = 0 ;
SYSTICK_CSR = 3 ; /* HBA / 8, Interrupt ON, Enable */
#if TICKDIV == 8
SYSTICK_CSR = 3 ; /* HCLK / 8, Interrupt ON, Enable */
#else
SYSTICK_CSR = 7 ; /* HCLK, Interrupt ON, Enable */
#endif
/* SysTick_Handler will execute every 1s from now on */
#ifdef LED_ON

8
adcmain.c
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@ -1,5 +1,5 @@
/* adcmain.c -- ADC reading of reference voltage and temperature sensor */
/* Copyright (c) 2020-2021 Renaud Fivet */
/* Copyright (c) 2020-2025 Renaud Fivet */
#include <stdio.h>
#include "system.h"
@ -7,7 +7,7 @@
#define RAW
#define TS_CAL2 ((const short *) 0x1FFFF7C2)
#define USER0 ((const unsigned char *) 0x1FFFF804)
//#define USER0 ((const unsigned char *) 0x1FFFF804)
int main( void) {
unsigned last = 0 ;
@ -41,11 +41,11 @@ int main( void) {
# else
* 10000 / 5336 ;
# endif
Vsample = 330 * calV / Vsample ;
Vsample = 3300 * calV / Vsample ;
#else
adc_vnt( VNT_VNC, &Vsample, &Csample) ;
#endif
printf( "%i.%i, %i.%i\n", Vsample / 100, Vsample % 100,
printf( "%i.%i, %i.%i\n", Vsample / 1000, Vsample % 1000,
Csample / 10, Csample % 10) ;
}
}

13
docs/34_adcvnt.html
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@ -39,7 +39,7 @@ The initialization steps:
<li> Configure acquisition direction and mode.
</ul>
<pre>
static void adc_init( void) {
const unsigned short *adc_init( unsigned channels) {
/* Enable ADC peripheral */
RCC_APB2ENR |= RCC_APB2ENR_ADCEN ;
/* Setup ADC sampling clock */
@ -64,13 +64,16 @@ static void adc_init( void) {
} while( !( ADC_ISR & ADC_ISR_ADRDY)) ;
/* Select inputs and precision */
ADC_CHSELR = 3 << 16 ; /* Channel 16: temperature, Channel 17: Vrefint */
ADC_CCR |= ADC_CCR_TSEN | ADC_CCR_VREFEN ;
ADC_CHSELR = channels ;
ADC_CCR |= (channels & (1 << 17)) << 5 ; /* VREFEN */
ADC_CCR |= (channels & (1 << 16)) << 7 ; /* TSEN */
ADC_SMPR = 7 ;
/* Select acquisition direction and mode */
/* Default scan direction (00) is Temperature before Voltage */
// ADC_CFGR1 &= ~ADC_CFGR1_SCANDIR ; /* Default 0 is low to high */
ADC_CFGR1 |= ADC_CFGR1_DISCEN ; /* Enable Discontinuous mode */
return TS_CAL1 ;
}
</pre>
@ -88,7 +91,7 @@ command, wait until completion and fetch the result in the ADC Data
Register.
<pre>
static unsigned adc_convert( void) {
unsigned adc_convert( void) {
/* Either only one channel in sequence or Discontinuous mode ON */
ADC_CR |= ADC_CR_ADSTART ; /* Start ADC conversion */
do {} while( ADC_CR & ADC_CR_ADSTART) ; /* Wait for start command cleared */
@ -196,7 +199,7 @@ calibration value addresses and the following implementation of
<pre>
void adc_vnt( vnt_cmd_t cmd, short *ptrV, short *ptrC) {
if( cmd == VNT_INIT)
adc_init() ;
adc_init( 3 << 16) ; /* 17: V, 16: T */
if( cmd <= VNT_CAL) {
/* Calibration Values */

109
docs/39_resistor.html
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@ -15,44 +15,113 @@ potentiometers, sliders, joysticks …
<h2>Voltage Divider Circuit</h2>
<img alt="Voltage Divider Circuit" src="img/39_vdivider.png">
<p>
<b>Vout = Vin * Rref / (Rref + Rmeasured)</b>
Reading a resistor value is based on the voltage divider circuit.<br>
<img alt="Voltage Divider Circuit" src="img/39_vdivider.png"><br>
The relationship between the two voltages, <b>Vin</b> and <b>Vout</b> is
<b><pre>
Vout Vin
────── = ──────────────
Rref Rref + Rmeas
</pre></b>
<h2>ADC Readings</h2>
Assuming the ADC is configured for 12 bit precision and return a value
in the range [0 … 4095]
<p>
<b>Vout = VADC = VDDA * ADCRAW / 4095</b>
<p>
<b>Vin = VDDA</b>
<p>
<b>~VDDA~ * ADCRAW / 4095 = ~VDDA~ * Rref / (Rref + Rmeasured)</b>
<p>
<b>ADCRAW * Rmeasured = Rref * (4095 – ADCRAW)</b>
<p>
<b>Rmeasured = Rref * (4095 – ADCRAW) / ADCRAW</b>
<p>
<b>Rmeasured = Rref * (4095 / ADCRAW – 1)</b>
in the range [0 … 4095], I can express the two voltages in terms of ADC values.
<br>
&nbsp;<b>Vout = VADC = VDDA * ADCraw / 4095</b><br>
&nbsp;<b>Vin = VDDA</b>
<p>The voltage divider relationship now becomes<br>
&nbsp;<b><i>VDDA</i> * ADCraw / 4095 = <i>VDDA</i> * Rref / (Rref + Rmeasured)</b>
<p>which can be further simplified as<br>
&nbsp;<b>ADCraw * Rmeasured = Rref * (4095 – ADCraw)</b>
<p>The resistor value is then given by<br>
&nbsp;<b>Rmeasured = Rref * (4095 – ADCraw) / ADCraw</b><br>
or<br>
&nbsp;<b>Rmeasured = Rref * (4095 / ADCraw – 1)</b>
<h2>Devil in the whatnots</h2>
Some of the things to pay attention to while coding
<ul>
<li> Avoiding division by zero.
<li> Integer versus floating point calculation.
<li> Choosing the reference resistor.
<li> Calibration of the reference resistor.
</ul>
<h3>● Division by Zero</h3>
In the case where ADC readings would return 0, I chose to return INT_MAX as
a value to flag the error.
<pre>
#include &lt;limits.h>
int R = ADCraw ? Rref * (4095 / ADCraw - 1) : INT_MAX ;
</pre>
<h3>● Integer Calculation</h3>
As integer based calculation tends to round intermediary results, I use the
developped formula
<pre>int R = ADCraw ? Rref * 4095 / ADCraw - Rref : INT_MAX ;</pre>
<hr>© 2020-2024 Renaud Fivet
<h3>● Reference Resistor Selection</h3>
The pair of resistors, reference and measured, has to be selected according
to the use case. For now I am experimenting with the measurement of a
photoresistor and use a reference resistor of 10 kOhm.
<h3>● Calibration</h3>
For resistor reading, the reference voltage value VDDA does not influence the
calculation. From a hardware design point of view, having a stable reference
voltage still remains a key factor in securing reliable ADC readings.<br>
For precise resistor value reading, the calibration of the reference resistor
will be key. In other cases, the raw ADC reading can be used in combination
with dynamic range acquisition.
<h2>Sampling Code</h2>
I create <b>adcext.c</b> to take readings every second.
<pre>
#include &lt;limits.h>
#include &lt;stdio.h>
#include "system.h" /* uptime, yield(), adc_init(), adc_convert() */
#define RREF 10010 /* Rref is 10kOhm, measured @ 10.01 kOhm */
int main( void) {
unsigned last = 0 ;
const unsigned short *calp ; /* TS_CAL, VREFINT_CAL */
/* Initialize ADC and fetch calibration values */
calp = adc_init( 2 | (1 << 17)) ; /* ADC read on GPIOA1 and VREF */
short Vcal = calp[ 1] ; /* VREFINT_CAL */
printf( "factory calibration: %u, %u, %u\n", calp[ 1], calp[ 0], calp[5]) ;
for( ;;)
if( uptime == last)
yield() ;
else {
short Rsample, Vsample ;
last = uptime ;
Vsample = adc_convert() ;
Rsample = adc_convert() ;
printf( "%i, %i, %i, ", Vcal, Vsample, Rsample) ;
int res = Rsample ? RREF * 4095 / Rsample - RREF : INT_MAX ;
Vsample = 3300 * Vcal / Vsample ;
printf( "%i, %i.%i\n", res, Vsample / 1000, Vsample % 1000) ;
}
}
</pre>
I add the composition in <b>Makefile</b>
<pre>SRCS = startup.crc.c adc.c adcext.c</pre>
<h2>Checkpoint</h2>
<p>
Building up on the previous ADC reading of internal sensors, sampling of
an external resistor pair connected to one of the IO pin is straightforward.
</p>
<hr>© 2020-2025 Renaud Fivet
</body>
</html>

2
system.h
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@ -30,5 +30,7 @@ typedef enum {
} vnt_cmd_t ;
void adc_vnt( vnt_cmd_t cmd, short *ptrV, short *ptrC) ;
const unsigned short *adc_init( unsigned channels) ;
unsigned adc_convert( void) ;
/* end of system.h */