embedded-systems

# Embedded Systems ## What I Do I specialize in embedded systems—computing systems designed for specific control functions within larger mechanical or electrical systems. My expertise spans microcontroller programming (ARM Cortex-M, AVR, PIC), bare-metal firmware development, real-time operating systems (FreeRTOS, Zephyr), peripheral interfaces (GPIO, UART, SPI, I2C, ADC, PWM), low-power design, hardware-software co-design, and embedded Linux systems. I work with resource constraints (memory, processing power, power consumption) while delivering reliable, deterministic, and efficient embedded solutions. ## When to Use Me - Developing firmware for microcontrollers and SoCs - Building IoT devices with strict power budgets - Implementing motor control, sensor interfaces, or actuator systems - Creating bare-metal drivers without an OS - Building RTOS-based applications with multiple tasks - Porting or customizing embedded Linux systems - Implementing bootloaders and secure boot - Optimizing code for resource-constrained environments ## Core Concepts 1. **Microcontroller Architecture**: ARM Cortex-M, Peripherals, Memory Maps, Clock Systems 2. **Peripheral Interfaces**: GPIO, UART, SPI, I2C, USB, CAN, ADC, DAC, PWM 3. **Interrupt Handling**: NVIC, vector tables, interrupt priorities, ISR design 4. **Memory Constraints**: Flash, RAM limitations, memory-mapped I/O 5. **Power Management**: Sleep modes, clock gating, dynamic voltage scaling 6. **Real-Time Constraints**: Deterministic timing, interrupt latency, task scheduling 7. **Communication Protocols**: UART, SPI, I2C, CAN, Bluetooth, WiFi stacks 8. **Bootloaders**: Firmware update mechanisms, secure boot, OTA updates 9. **Debugging**: JTAG, SWD, printf debugging, logic analyzers 10. **Safety and Reliability**: Watchdogs, CRC, error detection, fault handling ## Code Examples ```c // GPIO and Interrupt Handling on STM32 #include "stm32f4xx.h" #include "system_stm32f4xx.h" #define LED_PIN GPIO_ODR_ODR_12 #define BUTTON_PIN GPIO_IDR_ID0 volatile uint32_t button_press_count = 0; volatile uint32_t last_debounce_time = 0; #define DEBOUNCE_DELAY_MS 50 void GPIO_Init(void) { // Enable GPIOD clock (LED) and GPIOA (Button) RCC->AHB1ENR |= RCC_AHB1ENR_GPIODEN | RCC_AHB1ENR_GPIOAEN; // Configure LED pins (PD12-PD15) as output GPIOD->MODER &= ~GPIO_MODER_MODER12_0 | GPIO_MODER_MODER13_0 | GPIO_MODER_MODER14_0 | GPIO_MODER_MODER15_0; GPIOD->MODER |= GPIO_MODER_MODER12_0 | GPIO_MODER_MODER13_0 | GPIO_MODER_MODER14_0 | GPIO_MODER_MODER15_0; // Configure button pin (PA0) as input GPIOA->MODER &= ~GPIO_MODER_MODER0; GPIOA->PUPDR |= GPIO_PUPDR_PUPD0_1; // Pull-down // Configure interrupt for button (EXTI0) RCC->APB2ENR |= RCC_APB2ENR_SYSCFGEN; SYSCFG->EXTICR[0] &= ~SYSCFG_EXTICR1_EXTI0; SYSCFG->EXTICR[0] |= SYSCFG_EXTICR1_EXTI0_PA; EXTI->IMR |= EXTI_IMR_IM0; // Unmask interrupt EXTI->FTSR |= EXTI_FTSR_TR0; // Falling edge trigger EXTI->RTSR &= ~EXTI_RTSR_TR0; // Disable rising edge // Configure NVIC priority for EXTI0 interrupt NVIC_SetPriority(EXTI0_IRQn, 5); NVIC_EnableIRQ(EXTI0_IRQn); } void EXTI0_IRQHandler(void) { if (EXTI->PR & EXTI_PR_PR0) { uint32_t current_time = HAL_GetTick(); if (current_time - last_debounce_time > DEBOUNCE_DELAY_MS) { button_press_count++; last_debounce_time = current_time; // Toggle LED GPIOD->ODR ^= LED_PIN; } EXTI->PR |= EXTI_PR_PR0; // Clear interrupt flag } } void delay_ms(uint32_t ms) { SysTick->LOAD = (SystemCoreClock / 1000) * ms - 1; SysTick->VAL = 0; while (!(SysTick->CTRL & SysTick_CTRL_COUNTFLAG_Msk)); } int main(void) { SystemInit(); GPIO_Init(); while (1) { // Main loop - can be empty if using interrupts __WFI(); // Wait for interrupt } } ``` ```python # MicroPython I2C Sensor Interface from machine import Pin, I2C import time class BME280Sensor: """BME280 temperature, humidity, pressure sensor driver.""" BME280_ADDR = 0x76 REG_CTRL_HUM = 0xF2 REG_CTRL_MEAS = 0xF4 REG_CONFIG = 0xF5 REG_TEMP = 0xFA REG_HUM = 0xFD REG_PRESS = 0xF7 def __init__(self, scl_pin=22, sda_pin=21): self.i2c = I2C(scl=Pin(scl_pin), sda=Pin(sda_pin), freq=100000) self.dig = {} self._calibrate() def _read_u16(self, reg): """Read unsigned 16-bit value.""" data = self.i2c.readfrom_mem(self.BME280_ADDR, reg, 2) return (data[0] << 8) | data[1] def _read_s16(self, reg): """Read signed 16-bit value.""" val = self._read_u16(reg) if val > 32767: val -= 65536 return val def _calibrate(self): """Read calibration data from sensor.""" cal_data = self.i2c.readfrom_mem(self.BME280_ADDR, 0x88, 24) self.dig['T1'] = cal_data[0] | (cal_data[1] << 8) self.dig['T2'] = self._read_s16(0x88) self.dig['T3'] = self._read_s16(0x8C) self.dig['P1'] = self._read_u16(0x8E) self.dig['P2'] = self._read_s16(0x90) self.dig['P3'] = self._read_s16(0x92) self.dig['P4'] = self._read_s16(0x94) self.dig['P5'] = self._read_s16(0x96) self.dig['P6'] = self._read_s16(0x98) self.dig['P7'] = self._read_s16(0x9A) self.dig['P8'] = self._read_s16(0x9C) self.dig['P9'] = self._read_s16(0x9E) hum_cal = self.i2c.readfrom_mem(self.BME280_ADDR, 0xA1, 1)[0] self.dig['H1'] = hum_cal hum_cal2 = self.i2c.readfrom_mem(self.BME280_ADDR, 0xE1, 7) self.dig['H2'] = self._read_s16(0xE1) self.dig['H3'] = hum_cal2[2] self.dig['H4'] = (hum_cal2[4] << 4) | (hum_cal2[3] & 0x0F) self.dig['H5'] = (hum_cal2[5] << 4) | (hum_cal2[3] >> 4) self.dig['H6'] = hum_cal2[6] def _compensate_temp(self, adc_T): """Compensate temperature reading.""" var1 = (adc_T / 16384.0 - self.dig['T1'] / 1024.0) * self.dig['T2'] var2 = ((adc_T / 131072.0 - self.dig['T1'] / 8192.0) ** 2) * self.dig['T3'] return (var1 + var2) / 5120.0 def _compensate_press(self, adc_P, t_fine): """Compensate pressure reading.""" var1 = (t_fine / 2.0) - 64000.0 var2 = var1 * var1 * self.dig['P6'] / 32768.0 var2 = var2 + var1 * self.dig['P5'] * 2.0 var2 = (var2 / 4.0) + self.dig['P4'] * 65536.0 var1 = (self.dig['P3'] * var1 * var1 / 524288.0 + self.dig['P2'] * var1) / 524288.0 var1 = (1.0 + var1 / 32768.0) * self.dig['P1'] if var1 == 0: return 0 pressure = 1048576.0 - adc_P pressure = (pressure - var2 / 4096.0) * 6250.0 / var1 var1 = self.dig['P9'] * pressure * pressure / 2147483648.0 var2 = pressure * self.dig['P8'] / 32768.0 pressure = pressure + (var1 + var2 + self.dig['P7']) / 16.0 return pressure / 100.0 # hPa def read_all(self): """Read all sensor values.""" # Set mode to normal, read all self.i2c.writeto_mem(self.BME280_ADDR, self.REG_CTRL_HUM, b'\x05') self.i2c.writeto_mem(self.BME280_ADDR, self.REG_CTRL_MEAS, b'\x27') time.sleep_ms(10) adc_T = (self.i2c.readfrom_mem(self.BME280_ADDR, self.REG_TEMP, 3)[0] << 12) | \ (self.i2c.readfrom_mem(self.BME280_ADDR, self.REG_TEMP + 1, 1)[0] << 4) | \ (self.i2c.readfrom_mem(self.BME280_ADDR, self.REG_TEMP + 2, 1)[0] >> 4) t_fine = self._compensate_temp(adc_T) temperature = t_fine / 5120.0 adc_P = (self.i2c.readfrom_mem(self.BME280_ADDR, self.REG_PRESS, 3)[0] << 12) | \ (self.i2c.readfrom_mem(self.BME280_ADDR, self.REG_PRESS + 1, 1)[0] << 4) | \ (self.i2c.readfrom_mem(self.BME280_ADDR, self.REG_PRESS + 2, 1)[0] >> 4) pressure = self._compensate_press(adc_P, t_fine) return { 'temperature': temperature, 'pressure': pressure, 'humidity': 0 # Simplified } # Usage sensor = BME280Sensor() while True: values = sensor.read_all() print(f"Temp: {values['temperature']:.1f}C, Press: {values['pressure']:.1f}hPa") time.sleep(2) ``` ```c // FreeRTOS Task Management #include "FreeRTOS.h" #include "task.h" #include "queue.h" #include "semphr.h" #include <stdio.h> #define TASK_STACK_SIZE 128 typedef struct { uint8_t sensor_id; float value; uint32_t timestamp; } SensorData_t; QueueHandle_t sensor_queue; SemaphoreHandle_t uart_mutex; void vSensorTask(void *pvParameters) { uint8_t sensor_id = *(uint8_t *)pvParameters; TickType_t xLastWakeTime = xTaskGetTickCount(); while (1) { // Read sensor (simulated) float sensor_value = sensor_id * 0.1f + (rand() % 100) / 100.0f; // Create sensor data message SensorData_t data = { .sensor_id = sensor_id, .value = sensor_value, .timestamp = xTaskGetTickCount() }; // Send to queue with timeout if (xQueueSend(sensor_queue, &data, pdMS_TO_TICKS(10)) != pdTRUE) { // Handle queue full } vTaskDelayUntil(&xLastWakeTime, pdMS_TO_TICKS(100)); } } void vProcessingTask(void *pvParameters) { SensorData_t data; while (1) { if (xQueueReceive(sensor_queue, &data, portMAX_DELAY) == pdTRUE) { // Process sensor data xSemaphoreTake(uart_mutex, portMAX_DELAY); printf("Sensor %d: %.2f at %lu\n", data.sensor_id, data.value, data.timestamp); xSemaphoreGive(uart_mutex); } } } void vBlinkTask(void *pvParameters) { uint32_t led_pin = *(uint32_t *)pvParameters; while (1) { // Toggle LED GPIO_ToggleBits(GPIO_PORT, led_pin); vTaskDelay(pdMS_TO_TICKS(500)); } } int main(void) { // Hardware init Hardware_Init(); // Create queue sensor_queue = xQueueCreate(10, sizeof(SensorData_t)); if (sensor_queue == NULL) { // Handle error } // Create mutex for UART uart_mutex = xSemaphoreCreateMutex(); // Create tasks uint8_t sensor_ids[] = {1, 2, 3}; xTaskCreate(vSensorTask, "Sensor1", TASK_STACK_SIZE, &sensor_ids[0], 2, NULL); xTaskCreate(vSensorTask, "Sensor2", TASK_STACK_SIZE, &sensor_ids[1], 2, NULL); xTaskCreate(vSensorTask, "Sensor3", TASK_STACK_SIZE, &sensor_ids[2], 2, NULL); xTaskCreate(vProcessingTask, "Process", TASK_STACK_SIZE * 2, NULL, 3, NULL); uint32_t led_pin = GPIO_PIN_12; xTaskCreate(vBlinkTask, "Blink", TASK_STACK_SIZE, &led_pin, 1, NULL); // Start scheduler vTaskStartScheduler(); // Should never reach here while (1); } ``` ## Best Practices