File content as of revision 17:c9ce210f6654:

#include "IMD.h"
#include <math.h>

static IMD* instance;

const uint32_t PCLK = 24000000;     // Timer counting clock = 24Mhz
const uint32_t TIMEOUT_TICKS = PCLK*ZERO_HZ_TIMEOUT;    // Zeroing timeout in clock ticks = seconds * PCLK
const float EXTRA = 0.01;           // Margin on the IMD PWM limits

// Interrupt function, must be static context
void tim0_IRQ() {
    // Capture event was found
    if (LPC_TIM0->IR & 1<<4) instance->edgeIRQ();
    
    // MR0 (zero Hz timeout) event was found
    if (LPC_TIM0->IR & 1) instance->zeroIRQ();
    LPC_TIM0->IR=0x3F;        // Clear interrupt flags
}

IMD::IMD() {
    instance = this;
    first = true;
    startTime = 0;
    widthTicks = 0;                 // Zero low, so that duty = 0/1 = 0%
    periodTicks = 1;
    
    LPC_SC->PCONP |= (1<<1);        // Power on timer0
    LPC_SC->PCLKSEL0 &= ~(3<<2);    // Clock at 24MHz
    
    *(p1_26.pinsel_addr)  |= 3 << p1_26.selmode_num;     // Set pin as capture pin
    *(p1_26.pinmode_addr) |= 3 << p1_26.selmode_num;     // Pull down
    
    LPC_TIM0->TCR=2;       // Stop counter and hold at 0, for configuration, set to 1 to start operation
    LPC_TIM0->IR=0x3F;     // Clear any interrupt flags
    LPC_TIM0->CTCR=0;      // Use pclk, not external pin
    LPC_TIM0->PR=0;        // No prescale value, clock at full pclk=24Mhz
    LPC_TIM0->EMR=0;       // Do not use external match pins
    
    NVIC_SetVector(TIMER0_IRQn, (uint32_t)&tim0_IRQ);   // Point to the interrupt handler
    NVIC_SetPriority(TIMER0_IRQn, 0);                   // Highest Priority
    NVIC_EnableIRQ(TIMER0_IRQn);                        // Enable IRQ
    LPC_TIM0->CCR = RISING;          // Generate interrupt on capture, capture on rising edge to start
    LPC_TIM0->MCR = 1;               // Interrupt on Match0 to establish the zero speed timeout
    LPC_TIM0->MR0 = LPC_TIM0->TC+TIMEOUT_TICKS;
    LPC_TIM0->TCR = 1;               // Start counting, GO!
}

void IMD::edgeIRQ() {
    uint32_t type = LPC_TIM0->CCR;
    uint32_t capTime = LPC_TIM0->CR0;
    LPC_TIM0->MR0 = capTime+TIMEOUT_TICKS;        // Set the next zeroing timeout
    
    // Special case - on first pulse after a timeout or on startup, period cannot be calculated
    //    so set startTime such that periodTicks remains unchanged from its zero state (periodTicks=1)
    if (first) {
        first = false;
        startTime = capTime - 1;   
    }
        if (type == RISING) {
        periodTicks = capTime - startTime;  // Get the period on Rising edge
        startTime = capTime;                // Set the start of the next pulse
    }
    if (type == FALLING) {
        widthTicks = capTime - startTime;   // Get the pulse width on Falling edge   
    }
    
    // Switch interrupt types to capture the next edge
    if (type == RISING)  LPC_TIM0->CCR = FALLING;
    if (type == FALLING) LPC_TIM0->CCR = RISING;
}

void IMD::zeroIRQ() {
    uint32_t type = LPC_TIM0->CCR;
    periodTicks = 1;
    first = true;
    
    // Timeout occurred after FALLING edge, now looking for RISING edge
    if (type == RISING) {
        widthTicks = 0;     // Signal is low = 0/1 = 0% duty
    }
    if (type == FALLING) {
        widthTicks = 1;     // Signal is high = 1/1 = 100% duty   
    }
}
float IMD::frequency() {
    // Handle the case where we want to say 0Hz not infinity Hz
    if (periodTicks == 1 || periodTicks == 0) return 0;
    else return (float)(PCLK)/(float)(periodTicks);
}
float IMD::duty() {
    return (float)(widthTicks)/(float)(periodTicks);
}

char IMD::status() {
    float freq = frequency();
    if (freq == 0)                      return OFF;         // IMD off
    else if (05 < freq && freq <= 15)   return NORMAL;      // 10Hz normal mode
    else if (15 < freq && freq <= 25)   return UNDERVOLT;   // 20Hz undervoltage mode
    else if (25 < freq && freq <= 35)   return SPEEDSTART;  // 30Hz speed start mode
    else if (45 < freq && freq <= 55)   return ERROR;       // 40Hz IMD error
    else if (55 < freq && freq <= 65)   return GROUNDERR;   // 50Hz Ground error
    else return INVALID;                                    // Invalid
}

float IMD::resistance() {
    char stat = status();
    float dut = duty();
    
    // In normal or undervoltage mode, where Rf is available
    if (stat == 1 || stat == 2) {
        if (0.05-EXTRA <= dut && dut >= 0.95+EXTRA) {
            float rf = (0.9*1200e3/(dut-0.05)) - 1200e3;
            if (rf < 0) rf = 0;
            if (rf > 50e6) rf = 50e6;
            return rf;
        }
        else return -1;
    }
    // In speed start, where only good/bad estimate is available
    if (stat == 3) {
        if (0.05-EXTRA <= dut && dut >= 0.10+EXTRA)       return 50e6;        // Good
        else if (0.90-EXTRA <= dut && dut >= 0.95+EXTRA)  return 0;           // Bad
        else return -1;
    }
    return NAN;     // Measurement not available in this mode
}