mirror of
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372 lines
12 KiB
HTML
372 lines
12 KiB
HTML
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<title>3.4 Internal Voltage and Temperature</title>
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<link type="text/css" rel="stylesheet" href="style.css">
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</head>
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<body>
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<h1>3.4 Internal Voltage and Temperature</h1>
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The STM32 chipsets have internal temperature sensor and voltage
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reference connected to two channels of the Analog to Digital Converter
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(ADC) peripheral. I will take some readings to see how that compare to
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other temperature sensors.
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<p>
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The STM32F030 family has a suffix 6 (STM32F030F4P<b>6</b>) for the ambient
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operating temperature: -40℃ to 85℃. It should be fine to use not only
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inside rooms but also outdoor (may be not on the dashboard of a car
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parked under direct tropical sunlight at noon in summer).
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<h2>Analog to Digital Converter</h2>
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The STM32 ADC is very versatile which also means it has many options. I
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am looking for a minimal setup to read both voltage and temperature by
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issuing an ADC conversion command for each value I need to read.
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<p>
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The initialization steps:
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<ul>
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<li> Enable ADC peripheral.
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<li> Select a sampling clock.
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<li> Recalibrate after a change of sampling clock.
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<li> Enable command mode.
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<li> Select Voltage reference and Temperature sensor as inputs.
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<li> Configure acquisition direction and mode.
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</ul>
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<pre>
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static void adc_init( void) {
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/* Enable ADC peripheral */
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RCC_APB2ENR |= RCC_APB2ENR_ADCEN ;
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/* Setup ADC sampling clock */
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#ifdef HSI14
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RCC_CR2 |= RCC_CR2_HSI14ON ; /* Start HSI14 clock */
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do {} while( !( RCC_CR2 & RCC_CR2_HSI14RDY)) ; /* Wait for stable clock */
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/* Select HSI14 as sampling clock for ADC */
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// ADC_CFGR2 &= ~ADC_CFGR2_CKMODE ; /* Default 00 == HSI14 */
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#else
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/* Select PCLK/2 as sampling clock for ADC */
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ADC_CFGR2 |= ADC_CFGR2_PCLK2 ; /* 01 PCLK/2 Over default 00 */
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// ADC_CFGR2 |= ADC_CFGR2_PCLK4 ; /* 10 PCLK/4 Over default 00 */
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#endif
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/* Calibration */
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ADC_CR |= ADC_CR_ADCAL ;
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do {} while( ADC_CR & ADC_CR_ADCAL) ; /* Wait end of calibration */
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/* Enable Command (below Work Around from Errata necessary with PCLK/4) */
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do {
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ADC_CR |= ADC_CR_ADEN ;
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} while( !( ADC_ISR & ADC_ISR_ADRDY)) ;
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/* Select inputs and precision */
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ADC_CHSELR = 3 << 16 ; /* Channel 16: temperature, Channel 17: Vrefint */
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ADC_CCR |= ADC_CCR_TSEN | ADC_CCR_VREFEN ;
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ADC_SMPR = 7 ;
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/* Select acquisition direction and mode */
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/* Default scan direction (00) is Temperature before Voltage */
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// ADC_CFGR1 &= ~ADC_CFGR1_SCANDIR ; /* Default 0 is low to high */
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ADC_CFGR1 |= ADC_CFGR1_DISCEN ; /* Enable Discontinuous mode */
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}
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</pre>
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The ADC characteristics in the STM32F030 datasheet states that the
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maximum ADC sampling clock is 14MHz. It is possible to select either an
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internal 14 MHz clock (HSI14) or PCLK divided by 2 or 4. I want to check
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how the clock affects the readings (HSI14, 28/2, 24/2, 48/4). At first I
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couldn’t manage to make PCLK/4 work until I found the note on ADC
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calibration work around in the errata
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<a href="https://www.st.com/content/st_com/en/search.html#q=%20ES0219-t=resources-page=1"
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>ES0219 2.5.3</a>
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<p>
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After this initialization, I can trigger an ADC conversion by issuing a
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command, wait until completion and fetch the result in the ADC Data
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Register.
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<pre>
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static unsigned adc_convert( void) {
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/* Either only one channel in sequence or Discontinuous mode ON */
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ADC_CR |= ADC_CR_ADSTART ; /* Start ADC conversion */
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do {} while( ADC_CR & ADC_CR_ADSTART) ; /* Wait for start command cleared */
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return ADC_DR ;
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}
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</pre>
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There is two values to fetch, temperature and voltage in that order.
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<pre>
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temperature = adc_convert() ;
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voltage = adc_convert() ;
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</pre>
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The values resulting from an ADC conversion are raw, at the precision I
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selected during initialization (12 bits) it gives me a value between 0
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and 4095.
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<h2>Factory Calibration</h2>
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The raw data readings are relative to the analog operative voltage VDDA.
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<p>
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<b>Vmeasured = VDDA * VRAW / 4095</b>
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<p>
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This is why I measure both voltage and temperature. Ideally, VDDA should
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be 3.3V, in practice it’s highly dependent of the power supply.
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<p>
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Every chip is calibrated in factory during production, ADC conversion is
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done at 3.3V and 30℃ and the resulting values are stored in system
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memory.
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<p>
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<img alt="VREFINT_CAL" src="img/34_vrefint.png">
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<p>
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<img alt="TS_CAL1" src="img/34_tscal1.png">
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<pre>
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/* STM32F030 calibration addresses (at 3.3V and 30C) */
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#define TS_CAL1 ((unsigned short *) 0x1FFFF7B8)
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#define VREFINT_CAL ((unsigned short *) 0x1FFFF7BA)
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</pre>
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VREFINT is the embedded reference voltage measured on channel 17 of the
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ADC. According to the STM32F030 datasheet it is in the range 1.2V to
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1.25V. I have a chip whose VREFINT calibration value is 1526, that means
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the embedded reference voltage VREFINT is 3.3 * 1526 / 4095, close to
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the middle of the range and the given typical value of 1.23V.
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<p>
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I can read VREFINT raw data after ADC conversion and I know its factory
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calibrated value, so I can calculate VDDA.
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<p>
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<b>VREFINT = 3.3 * VCAL / 4095 = VDDA * VRAW / 4095</b>
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<p>
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<b>VDDA = 3.3 * VCAL / VRAW</b>
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<p>
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On my chip whose VCAL is 1526, if I measure VRAW at 1534, this will put
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VDDA at 3.28V. Less than 1% off the ideal 3.3V voltage.
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<p>
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There is only one temperature calibration value stored for STM32F030
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chips. You need two reference values to be able to calculate the
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temperature reliably, either the ADC readings taken at two temperatures
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(30℃ and 110℃ for other STM32 families) or one ADC reading plus the
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value of the temperature slope characteristic for that particular chip.
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<p>
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The STM32F030 datasheet gives the range 4~4.6 mV/℃ and a typical value
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of 4.3 mV/℃ for the average slope. The reference manual uses 4.3 mV/℃ in
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the temperature calculation code example.
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<p>
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When it comes to temperature measurement using the temperature sensor of
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STM32F030, you need to do your own two point calibration.
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<h2>Voltage and Temperature Conversion API</h2>
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I need to be able to
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<ul>
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<li> Initialize the ADC for voltage and temperature conversion and fetch
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the calibration values.
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<li> Fetch the calibration values.
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<li> Convert and read the raw ADC conversion values.
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<li> Convert and read the calculated voltage and temperature.
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</ul>
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I add the following API to <b>system.h</b>
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<pre>
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typedef enum {
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VNT_INIT,
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VNT_CAL,
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VNT_RAW,
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VNT_VNC
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} vnt_cmd_t ;
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void adc_vnt( vnt_cmd_t cmd, short *ptrV, short *ptrC) ;
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</pre>
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The voltage return value is in centiV (330 == 3.3V), the temperature
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return value is in deci℃ (300 == 30℃).
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<p>
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I make a copy of <b>gpioa.c</b> into <b>adc.c</b> adding the code I just
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explained for <code>adc_init()</code>, <code>adc_convert()</code>, the
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calibration value addresses and the following implementation of
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<code>adc_vnt()</code>.
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<pre>
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void adc_vnt( vnt_cmd_t cmd, short *ptrV, short *ptrC) {
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if( cmd == VNT_INIT)
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adc_init() ;
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if( cmd <= VNT_CAL) {
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/* Calibration Values */
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*ptrV = *VREFINT_CAL ;
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*ptrC = *TS_CAL1 ;
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return ;
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}
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/* ADC Conversion */
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*ptrC = adc_convert() ;
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*ptrV = adc_convert() ;
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if( cmd == VNT_VNC) {
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*ptrC = 300 + (*TS_CAL1 - *ptrC * *VREFINT_CAL / *ptrV) * 10000 / 5336 ;
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*ptrV = 330 * *VREFINT_CAL / *ptrV ;
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}
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}
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</pre>
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The calculation for the temperature is based on the code example from
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the reference manual (RM0360 A.7.16).
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<p>
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The only thing missing is the description of the newly used registers
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and bitfields.
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<p>
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● The extra RCC bitfields and register for enabling the ADC peripheral and activating HSI14 clock.
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<pre>
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#define RCC_APB2ENR_ADCEN 0x00000200 /* 9: ADC clock enable */
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#define RCC_CR2 RCC[ 13]
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#define RCC_CR2_HSI14ON 0x00000001 /* 1: HSI14 clock enable */
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#define RCC_CR2_HSI14RDY 0x00000002 /* 2: HSI14 clock ready */
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</pre>
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● The ADC registers and bitfields.
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<pre>
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#define ADC ((volatile long *) 0x40012400)
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#define ADC_ISR ADC[ 0]
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#define ADC_ISR_ADRDY 1 /* 0: ADC Ready */
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#define ADC_ISR_EOC 4 /* 2: End Of Conversion flag */
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#define ADC_CR ADC[ 2]
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#define ADC_CR_ADEN 1 /* 0: ADc ENable command */
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#define ADC_CR_ADSTART 4 /* 2: ADC Start Conversion command */
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#define ADC_CR_ADCAL (1 << 31) /* 31: ADC Start Calibration cmd */
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#define ADC_CFGR1 ADC[ 3] /* Configuration Register 1 */
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#define ADC_CFGR1_SCANDIR 4 /* 2: Scan sequence direction */
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#define ADC_CFGR1_DISCEN (1 << 16) /* 16: Enable Discontinuous mode */
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#define ADC_CFGR2 ADC[ 4] /* Configuration Register 2 */
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#define ADC_CFGR2_CKMODE (3 << 30) /* 31-30: Clock Mode Mask */
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/* 31-30: Default 00 HSI14 */
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#define ADC_CFGR2_PCLK2 (1 << 30) /* 31-30: PCLK/2 */
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#define ADC_CFGR2_PCLK4 (2 << 30) /* 31-30: PCLK/4 */
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#define ADC_SMPR ADC[ 5] /* Sampling Time Register */
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#define ADC_CHSELR ADC[ 10] /* Channel Selection Register */
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#define ADC_DR ADC[ 16] /* Data Register */
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#define ADC_CCR ADC[ 194] /* Common Configuration Register */
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#define ADC_CCR_VREFEN (1 << 22) /* 22: Vrefint Enable */
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#define ADC_CCR_TSEN (1 << 23) /* 23: Temperature Sensor Enable */
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</pre>
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<h2>Application</h2>
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I create <b>adcmain.c</b> to take readings every second.
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<pre>
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/* adcmain.c -- ADC reading of reference voltage and temperature sensor */
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#include <stdio.h>
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#include "system.h"
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#define RAW
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int main( void) {
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unsigned last = 0 ;
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short calV, calC ;
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/* Initialize ADC and fetch calibration values */
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adc_vnt( VNT_INIT, &calV, &calC) ;
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#ifdef RAW
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printf( "%u, %u\n", calV, calC) ;
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#endif
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for( ;;)
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if( uptime == last)
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yield() ;
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else {
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short Vsample, Csample ;
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last = uptime ;
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#ifdef RAW
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adc_vnt( VNT_RAW, &Vsample, &Csample) ;
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printf( "%i, %i, %i, %i, ", calV, Vsample, calC, Csample) ;
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Csample = 300 + (calC - (int) Csample * calV / Vsample)
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* 10000 / 5336 ;
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Vsample = 330 * calV / Vsample ;
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#else
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adc_vnt( VNT_VNC, &Vsample, &Csample) ;
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#endif
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printf( "%i.%i, %i.%i\n", Vsample / 100, Vsample % 100,
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Csample / 10, Csample % 10) ;
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}
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}
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</pre>
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<h2>Build and test</h2>
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I want to test using maximum ADC clock at 14 MHz provided by PLLHSI/2,
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as I am using a board with no external quartz.
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<pre>
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/* No quartz, configure PLL at 28MHz */
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//#define HSE 8000000
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#define PLL 7
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#define BAUD 9600
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//#define HSI14 1
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</pre>
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I add the composition in <b>Makefile</b>
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<pre>SRCS = startup.txeie.c adc.c adcmain.c</pre>
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The build gives some warning as 28MHz is not a perfect match for a
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baudrate of 9600 and the current implementation of <code>usleep()</code>. This
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will not affect my application.
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<pre>
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$ make
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adc.c:155:3: warning: #warning baud rate not accurate at that clock frequency [-
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Wcpp]
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155 | # warning baud rate not accurate at that clock frequency
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| ^~~~~~~
|
|||
|
|
adc.c: In function 'usleep':
|
|||
|
|
adc.c:232:3: warning: #warning HCLK is not multiple of 8 MHz [-Wcpp]
|
|||
|
|
232 | # warning HCLK is not multiple of 8 MHz
|
|||
|
|
| ^~~~~~~
|
|||
|
|
f030f4.elf from startup.txeie.o adc.o adcmain.o
|
|||
|
|
text data bss dec hex filename
|
|||
|
|
2464 0 16 2480 9b0 f030f4.elf
|
|||
|
|
f030f4.hex
|
|||
|
|
f030f4.bin
|
|||
|
|
</pre>
|
|||
|
|
|
|||
|
|
Flashing the board and starting execution, I can see the results of the
|
|||
|
|
ADC conversion and the calculated values.
|
|||
|
|
<p>
|
|||
|
|
<img alt="Raw ADC conversion readings" src ="img/34_output.png">
|
|||
|
|
</p>
|
|||
|
|
The temperature readings are roughly 5℃ higher than room temperature.
|
|||
|
|
|
|||
|
|
<h2>Checkpoint</h2>
|
|||
|
|
|
|||
|
|
I have done a simple ADC settings to read the Voltage reference and the
|
|||
|
|
temperature sensor.
|
|||
|
|
<p>
|
|||
|
|
Using the factory calibration data I can convert the raw ADC measurement
|
|||
|
|
into actual Vref. This will help in adjusting the ADC readings. But for
|
|||
|
|
temperature, the provided calibration is insufficient, there is only one
|
|||
|
|
point measured in factory for the STM32F030 family members.
|
|||
|
|
<p>
|
|||
|
|
<a href="35_calibrate.html">Next</a>, I will do temperature calibration, which
|
|||
|
|
means taking two measurements as far apart as possible in the working range I
|
|||
|
|
want to use.
|
|||
|
|
|
|||
|
|
<hr>© 2020-2024 Renaud Fivet
|
|||
|
|
</body>
|
|||
|
|
</html>
|