Light Detector - Robotic Arm Controller

Dual PIC16F877A system for tracking close light with servos.

Code

PWM State Machine

Compare mode (the hard way) because hardware PWM is too friggin short man...

typedef void (*state_handler)(pwm_controller* ctrl);

void action_high(pwm_controller* ctrl) {
    PORTB1 = false;
    CCPR1 = ctrl->low_period;
    ctrl->state = LOW;
}

static const state_transition state_table[PWM_STATE_COUNT] = {
    [HIGH] = { .state = LOW, .handler = action_high },
    [LOW]  = { .state = HIGH, .handler = action_low }
};

void handle_interrupt() {
    state_table[config->state].handler(config);
}

UART Ring Buffer

Lock-free, say what...

typedef struct {
    char buffer[UART_TX_BUFFER_SIZE];
    volatile unsigned char head;
    volatile unsigned char tail;
} uart_tx_circular_buffer;

bool tx_buffer_try_enqueue(const char data) {
    if (tx_buffer_is_full()) return false;
    tx_ring_buffer.buffer[tx_ring_buffer.head] = data;
    tx_ring_buffer.head = (tx_ring_buffer.head + 1) % UART_TX_BUFFER_SIZE;
    return true;
}

Interrupt Descriptors

typedef struct {
    interrupt_handler_t handler;
    volatile unsigned char* flag_reg;
    unsigned char flag_mask;
    flag_clear_type clear_type;
} interrupt_descriptor;

void __interrupt() isr(void) {
    if (*descriptor->flag_reg & descriptor->flag_mask) {
        descriptor->handler();
    }
}

Build

cmake --preset=xc8 && cmake --build build-xc8

Stack

PIC16F877A @ 20MHz • XC8 • 555 words of program space