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Merge pull request #7045 from jepler/smaller-microcontroller-temperat…
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…ure-samd

samd: Size-optimize the temperature code with an 0.5 to 2.0 degree relative additional error
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@dhalbert
dhalbert committed Oct 13, 2022
2 parents dce4c9d + ead03cd commit 1569c7e
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102 changes: 50 additions & 52 deletions ports/atmel-samd/common-hal/microcontroller/Processor.c
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Original file line number Diff line number Diff line change
Expand Up @@ -73,101 +73,99 @@
#include "peripheral_clk_config.h"

#define ADC_TEMP_SAMPLE_LENGTH 4
#define INT1V_VALUE_FLOAT 1.0
#define INT1V_DIVIDER_1000 1000.0
#define ADC_12BIT_FULL_SCALE_VALUE_FLOAT 4095.0
#define INT1V_VALUE_FLOAT MICROPY_FLOAT_CONST(1.0)
#define INT1V_DIVIDER_1000 MICROPY_FLOAT_CONST(1000.0)
#define ADC_12BIT_FULL_SCALE_VALUE_FLOAT MICROPY_FLOAT_CONST(4095.0)

// channel argument (ignored in calls below)
#define IGNORED_CHANNEL 0

// Decimal to fraction conversion. (adapted from ASF sample).
STATIC float convert_dec_to_frac(uint8_t val) {
float float_val = (float)val;
if (val < 10) {
return float_val / 10.0;
} else if (val < 100) {
return float_val / 100.0;
} else {
return float_val / 1000.0;
}
}

// Extract the production calibration data information from NVM (adapted from ASF sample),
// then calculate the temperature
//
// This code performs almost all operations with scaled integers. For
// instance, tempR is in units of 1/10°C, INT1VR is in units of 1mV, etc,
// This is important to reduce the code size of the function. The effect on
// precision is a ~.9°C difference vs the floating point algorithm on an
// approximate 0..60°C range with a difference of ~.5°C at 25°C. When the fine
// calculation step is skipped, the additional error approximately doubles.
//
// To save code size, rounding is neglected. However, trying to add back rounding
// (by computing (a + b/2) / b instead of just a / b) actually didn't help
// accuracy anyway.
#ifdef SAMD21
STATIC float calculate_temperature(uint16_t raw_value) {
volatile uint32_t val1; /* Temperature Log Row Content first 32 bits */
volatile uint32_t val2; /* Temperature Log Row Content another 32 bits */
uint8_t room_temp_val_int; /* Integer part of room temperature in °C */
uint8_t room_temp_val_dec; /* Decimal part of room temperature in °C */
uint8_t hot_temp_val_int; /* Integer part of hot temperature in °C */
uint8_t hot_temp_val_dec; /* Decimal part of hot temperature in °C */
int8_t room_int1v_val; /* internal 1V reference drift at room temperature */
int8_t hot_int1v_val; /* internal 1V reference drift at hot temperature*/

float tempR; // Production Room temperature
float tempH; // Production Hot temperature
float INT1VR; // Room temp 2's complement of the internal 1V reference value
float INT1VH; // Hot temp 2's complement of the internal 1V reference value
uint16_t ADCR; // Production Room temperature ADC value
uint16_t ADCH; // Production Hot temperature ADC value
float VADCR; // Room temperature ADC voltage
float VADCH; // Hot temperature ADC voltage
uint32_t val1; /* Temperature Log Row Content first 32 bits */
uint32_t val2; /* Temperature Log Row Content another 32 bits */
int room_temp_val_int; /* Integer part of room temperature in °C */
int room_temp_val_dec; /* Decimal part of room temperature in °C */
int hot_temp_val_int; /* Integer part of hot temperature in °C */
int hot_temp_val_dec; /* Decimal part of hot temperature in °C */
int room_int1v_val; /* internal 1V reference drift at room temperature */
int hot_int1v_val; /* internal 1V reference drift at hot temperature*/

uint32_t *temp_log_row_ptr = (uint32_t *)NVMCTRL_TEMP_LOG;

val1 = *temp_log_row_ptr;
temp_log_row_ptr++;
val2 = *temp_log_row_ptr;

room_temp_val_int = (uint8_t)((val1 & FUSES_ROOM_TEMP_VAL_INT_Msk) >> FUSES_ROOM_TEMP_VAL_INT_Pos);
room_temp_val_dec = (uint8_t)((val1 & FUSES_ROOM_TEMP_VAL_DEC_Msk) >> FUSES_ROOM_TEMP_VAL_DEC_Pos);
room_temp_val_int = ((val1 & FUSES_ROOM_TEMP_VAL_INT_Msk) >> FUSES_ROOM_TEMP_VAL_INT_Pos);
room_temp_val_dec = ((val1 & FUSES_ROOM_TEMP_VAL_DEC_Msk) >> FUSES_ROOM_TEMP_VAL_DEC_Pos);

hot_temp_val_int = (uint8_t)((val1 & FUSES_HOT_TEMP_VAL_INT_Msk) >> FUSES_HOT_TEMP_VAL_INT_Pos);
hot_temp_val_dec = (uint8_t)((val1 & FUSES_HOT_TEMP_VAL_DEC_Msk) >> FUSES_HOT_TEMP_VAL_DEC_Pos);
hot_temp_val_int = ((val1 & FUSES_HOT_TEMP_VAL_INT_Msk) >> FUSES_HOT_TEMP_VAL_INT_Pos);
hot_temp_val_dec = ((val1 & FUSES_HOT_TEMP_VAL_DEC_Msk) >> FUSES_HOT_TEMP_VAL_DEC_Pos);

// necessary casts: must interpret 8 bits as signed
room_int1v_val = (int8_t)((val1 & FUSES_ROOM_INT1V_VAL_Msk) >> FUSES_ROOM_INT1V_VAL_Pos);
hot_int1v_val = (int8_t)((val2 & FUSES_HOT_INT1V_VAL_Msk) >> FUSES_HOT_INT1V_VAL_Pos);

ADCR = (uint16_t)((val2 & FUSES_ROOM_ADC_VAL_Msk) >> FUSES_ROOM_ADC_VAL_Pos);
ADCH = (uint16_t)((val2 & FUSES_HOT_ADC_VAL_Msk) >> FUSES_HOT_ADC_VAL_Pos);

tempR = room_temp_val_int + convert_dec_to_frac(room_temp_val_dec);
tempH = hot_temp_val_int + convert_dec_to_frac(hot_temp_val_dec);
int ADCR = ((val2 & FUSES_ROOM_ADC_VAL_Msk) >> FUSES_ROOM_ADC_VAL_Pos);
int ADCH = ((val2 & FUSES_HOT_ADC_VAL_Msk) >> FUSES_HOT_ADC_VAL_Pos);

INT1VR = 1 - ((float)room_int1v_val / INT1V_DIVIDER_1000);
INT1VH = 1 - ((float)hot_int1v_val / INT1V_DIVIDER_1000);
int tempR = 10 * room_temp_val_int + room_temp_val_dec;
int tempH = 10 * hot_temp_val_int + hot_temp_val_dec;

VADCR = ((float)ADCR * INT1VR) / ADC_12BIT_FULL_SCALE_VALUE_FLOAT;
VADCH = ((float)ADCH * INT1VH) / ADC_12BIT_FULL_SCALE_VALUE_FLOAT;
int INT1VR = 1000 - room_int1v_val;
int INT1VH = 1000 - hot_int1v_val;

float VADC; /* Voltage calculation using ADC result for Coarse Temp calculation */
float VADCM; /* Voltage calculation using ADC result for Fine Temp calculation. */
float INT1VM; /* Voltage calculation for reality INT1V value during the ADC conversion */
int VADCR = ADCR * INT1VR;
int VADCH = ADCH * INT1VH;

VADC = ((float)raw_value * INT1V_VALUE_FLOAT) / ADC_12BIT_FULL_SCALE_VALUE_FLOAT;
int VADC = raw_value * 1000;

// Hopefully compiler will remove common subepxressions here.

// calculate fine temperature using Equation1 and Equation
// 1b as mentioned in data sheet section "Temperature Sensor Characteristics"
// of Electrical Characteristics. (adapted from ASF sample code).
// Coarse Temp Calculation by assume INT1V=1V for this ADC conversion
float coarse_temp = tempR + (((tempH - tempR) / (VADCH - VADCR)) * (VADC - VADCR));
int coarse_temp = tempR + (tempH - tempR) * (VADC - VADCR) / (VADCH - VADCR);

#if CIRCUITPY_FULL_BUILD
// Calculation to find the real INT1V value during the ADC conversion
int INT1VM; /* Voltage calculation for reality INT1V value during the ADC conversion */

INT1VM = INT1VR + (((INT1VH - INT1VR) * (coarse_temp - tempR)) / (tempH - tempR));

VADCM = ((float)raw_value * INT1VM) / ADC_12BIT_FULL_SCALE_VALUE_FLOAT;
int VADCM = raw_value * INT1VM;

// Fine Temp Calculation by replace INT1V=1V by INT1V = INT1Vm for ADC conversion
float fine_temp = tempR + (((tempH - tempR) / (VADCH - VADCR)) * (VADCM - VADCR));
float fine_temp = tempR + (((tempH - tempR) * (VADCM - VADCR)) / (VADCH - VADCR));

return fine_temp;
return fine_temp / 10;
#else
return coarse_temp / 10.;
#endif
}
#endif // SAMD21

#ifdef SAM_D5X_E5X
// Decimal to fraction conversion. (adapted from ASF sample).
STATIC float convert_dec_to_frac(uint8_t val) {
return val / MICROPY_FLOAT_CONST(10.);
}
STATIC float calculate_temperature(uint16_t TP, uint16_t TC) {
uint32_t TLI = (*(uint32_t *)FUSES_ROOM_TEMP_VAL_INT_ADDR & FUSES_ROOM_TEMP_VAL_INT_Msk) >> FUSES_ROOM_TEMP_VAL_INT_Pos;
uint32_t TLD = (*(uint32_t *)FUSES_ROOM_TEMP_VAL_DEC_ADDR & FUSES_ROOM_TEMP_VAL_DEC_Msk) >> FUSES_ROOM_TEMP_VAL_DEC_Pos;
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6 changes: 5 additions & 1 deletion shared-bindings/microcontroller/Processor.c
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Original file line number Diff line number Diff line change
Expand Up @@ -104,7 +104,11 @@ MP_PROPERTY_GETTER(mcu_processor_reset_reason_obj,
//| temperature: Optional[float]
//| """The on-chip temperature, in Celsius, as a float. (read-only)
//|
//| Is `None` if the temperature is not available."""
//| Is `None` if the temperature is not available.
//|
//| .. note :: On small SAMD21 builds without external flash,
//| the reported temperature has reduced accuracy and precision, to save code space.
//| """
STATIC mp_obj_t mcu_processor_get_temperature(mp_obj_t self) {
float temperature = common_hal_mcu_processor_get_temperature();
return isnan(temperature) ? mp_const_none : mp_obj_new_float(temperature);
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