File content as of revision 4:e0dbf2bdb967:

#include "mbed.h"
#include "main.h"

Serial pc(SERIAL_TX, SERIAL_RX, 115200); // tx, rx
//DigitalOut led(LED_RED);
//SPI spi(PTC6,PTC7,PTD1,PTC0);
//SPI spi(PTC6,PTC7,PTD1); // my prefered, but mixed
SPI spi(PTC6,PTC7,PTC5); // PTC5 - the LED
//SPI spi(PTD2,PTD3,PTD1);
DigitalOut cs(PTC0);

int main()
{
    int PROM[8];
    uint32_t D1,D2;
    double T,P;
    cs.write(1); // disable all SPI
    pc.printf("Hello World!\r\n");
    MS5611_init(PROM);
    for (int i=0; i<8; i++) {
        pc.printf("Prom(%i): %i\r\n",i,PROM[i]);
    }
    
    while (1) {
    // the third paramater gives over samping
    // 0 - 256
    // 1 - 512
    // 2 - 1024
    // 3 - 2048
    // 4 - 4096
    MS5611(&D1,&D2,4);
    pc.printf("%i\t%i\t",D1,D2);

    MS5611_phys(D1,D2,PROM,&T,&P);

    pc.printf("%f\t",T/100.0);
    pc.printf("%f\r\n",P/100.0);

    wait(1.0);
    }
}

void MS5611_init(int *PROM)
{
    uint32_t crc=0;
    spi.format(8,0); // 8 bit mode 0 - this is default anyway but good to code.
    spi.frequency(1000000); // 1MHz is this the minimum?
    cs.write(0); // Enable the MS5611 intercae
    if (spi.write(0x1E)!=0xfe) {
        pc.printf("Error reseting the device\r\n");
    }
    wait_ms(3); // give time for ROM to reload 2.8ms by the spec
    cs.write(1); // close the connection - does it finish the command?
    wait_us(10); // Pause after putting CSB high
    for (int i=0; i<8; i++) {
        cs.write(0); // enable the SC to start a command.
        if (spi.write(0xA0|(i<<1))!=0xfe) {
            pc.printf("Error reading prom(%i)\r\n",i);
        }
        register uint8_t promh=spi.write(0x00);
        register uint8_t proml=spi.write(0x00);
        cs.write(1); // disable CS to finish the command
        PROM[i]=((promh<<8)|(proml));
        crc|=(i==7)?(PROM[i]&0xff00):PROM[i]; // Note AN520 gives this bit mask
        for (int j=0; j<16; j++) {
            crc=crc<<1;
            if (crc&0x1000000) { // implimt the CRC4 algorithm 0x13 -
                crc^=0x1300000; // This won't do the last 4 bits of PROM7
            }
        }
        wait_us(10); // Pause probably not stricly needed, but after switching CSB high give a bit of time.
    }
    if ((crc>>20)!=(PROM[7]&0xf))
        pc.printf("CRC check sum: %x vs recorded %x\r\n",crc>>20,PROM[7]&0xf);
}

void MS5611(uint32_t *D1, uint32_t *D2, int os)
{
    //  cs.write(0);
    spi.format(8,0);
    spi.frequency(1000000);
    cs.write(0); // Enable the MS5611 intercae
    if (spi.write(0x1E)!=0xfe) { // and reset the device
        pc.printf("Error reseting the device\r\n");
    }
    wait_ms(3); // give time for ROM to reload 2.8ms by the spec
    cs.write(1); // close the connection - does it finish the command?
    wait_us(10); // Pause after putting CSB high
    cs.write(0); // Enable the MS5611 intercae
    if (spi.write(0x40|(os<<1))!=0xfe) { // D1 please
        pc.printf("Error asking for D1\r\n");
    }
    cs.write(1); // Disable the MS5611 intercae
    wait_us(600*(1<<os)); // pause for read, longer when oversampling
    cs.write(0); // Enable the MS5611 intercae
    if(spi.write(0x00)!=0xfe) { // can I have the result?;
        pc.printf("Error reading D1\r\n");
    }
    *D1=((uint32_t) spi.write(0x00))<<16;
    *D1|=((uint32_t) spi.write(0x00))<<8;
    *D1|=((uint32_t) spi.write(0x00));
    cs.write(1); // and terminate the command
    wait_us(10); // Pause after putting CSB high
    cs.write(0); // Enable the MS5611 intercae
    if (spi.write(0x50|(os<<1))!=0xfe) { // D2 please
        pc.printf("Error asking for D2\r\n");
    }
    cs.write(1); // Disable the MS5611 intercae
    wait_us(600*(1<<os)); // pause for read, longer when oversampling
    cs.write(0); // Enable the MS5611 intercae
    if(spi.write(0x00)!=0xfe) { // can I have the result?;
        pc.printf("Error reading D2\r\n");
    }
    *D2=((uint32_t) spi.write(0x00))<<16;
    *D2|=((uint32_t) spi.write(0x00))<<8;
    *D2|=((uint32_t) spi.write(0x00));
    cs.write(1); // and terminate the command
}

void MS5611_phys(uint32_t D1,uint32_t D2, int *PROM, double *T, double *P)
{
    int64_t dt=((int64_t) D2)-(((int64_t) PROM[5])<<8);
    *T=2000.0+((double) dt*PROM[6])/8388608.0;
    int64_t off128=(((int64_t) PROM[2])<<23)+(((int64_t) PROM[4])*dt);
    int64_t sens256=(((int64_t) PROM[1])<<23)+(((int64_t) PROM[3])*dt);
    *P=(((double) D1)*((double) sens256)/4194304.0-((double) off128))/4194304.0;
}