File content as of revision 1:20b452641613:

// fc1114 - Frequency counter with i2c slave.
// target: LPC1114FN28

#include "mbed.h"

#define I2C_ADRS 0x70

DigitalOut led(dp28);
I2CSlave slave(dp5, dp27);
Ticker tick;

volatile uint32_t frq;

void isr_tick(){
    frq = LPC_TMR32B0->TC;
    LPC_TMR32B0->TC = 0;

    led = !led;
}
    
int main() {
    union {
        char b[4];
        uint32_t w;
    } buf;
    char dummy[4];

    led = 1;
    tick.attach(&isr_tick, 1);

    LPC_SYSCON->SYSAHBCLKCTRL |= (1 << 9);//TMR32B0 wakeup
    LPC_IOCON->PIO1_5 |= (1 << 1);// Set PIN14 as CT32B0_CAP0
    LPC_IOCON->PIO1_5 |= (1 << 5);// Hysteresis enable
    LPC_TMR32B0->TCR = 2; // reset
    LPC_TMR32B0->CTCR  = 1; // counter mode
    LPC_TMR32B0->CCR  = 0; // Input Capture Disable)
    LPC_TMR32B0->PR  = 0;// no prescale
    LPC_TMR32B0->TCR = 1; // start

    slave.address(I2C_ADRS << 1);
    
    while (1) {
        int i = slave.receive();
        switch (i) {
            case I2CSlave::ReadAddressed:
                buf.w = frq;
                slave.write(buf.b, 4);
                break;
            case I2CSlave::WriteGeneral:
                slave.read(dummy, 4);
                break;
            case I2CSlave::WriteAddressed:
                slave.read(dummy, 4);
                break;
        }
    }
}