File content as of revision 0:52ce2a69824f:

// Code to implement ICSP of an AVR using the ISP on the mBed pins 5,6,7 
// and 8 as RESET

//NOTES:    -load hex file onto the mBed as a file named "avr"
//          -Change TARGET_CLK to a suiteable value for your particular avr (it gets divided by 2 for ATMega88)
//          -Change the max page size to suite the microcontroller (change the 64 only)

#include "mbed.h"
#define LSB(I) ((I) & 0xFF)
#define MSB(I) (((I) & 0xF00) >> 8)

#define TARGET_CLK 1000000L
#define MAX_PAGE_SIZE (64 >> 1) //divide max page size by 2 to get number of words per page                                    
                                                   
SPI spi(p5, p6, p7); // mosi, miso, sclk/
DigitalOut reset(p8);   //RESET

Serial pc(USBTX, USBRX); // tx, rx

LocalFileSystem local("local");


int enable_prog_mode() //function to enable prog mode
{
    int failed = 0;
    
    while(failed < 5) //loop to try to enable programming mode 5 times
    {
        spi.write(0xAC);
        spi.write(0x53);
        int prog_en_check = spi.write(0x00);
        if(prog_en_check == 0x53) { //if data read on 3rd byte load is 0x53
            spi.write(0x00);        //programming mode was enabled...good job!
            pc.printf("\nProgramming mode enabled...\n");
            return 0;
        }      
        else{
            pc.printf("Programming mode failed!\n");
            pc.printf("%d\n",prog_en_check); 
            failed++;
            reset = 1; //pulse reset and try again
            reset = 0;
            pc.printf("Trying again...\n");
            wait(0.5);
        }
     }
    return -1; //Bummer...
}

//A function to poll BSY to prevent loading a new instruction prematurely
void still_programming() 
{
    int check = 1;
    while(check == 1)
    {
        spi.write(0xF0);
        spi.write(0x00);
        spi.write(0x00);
        check = spi.write(0x00); //read data byte out
    }
}

//A function to send the chip erase command
void chip_erase() 
{
        pc.printf("Chip erase initiated...\n");
        spi.write(0xAC);
        spi.write(0x80);
        spi.write(0x00);
        spi.write(0x00);
        still_programming();
        pc.printf("Chip erase completed!\n");
        reset = 1;
        wait(0.020);
        reset = 0;
        wait(0.020);
        enable_prog_mode();
}


void write_prog_page(uint16_t addr)
{
    //write program memory page
    spi.write(0x4C);
    spi.write(MSB(addr));
    spi.write(LSB(addr));
    spi.write(0x00);
    still_programming(); //make sure the operation worked
   // pc.printf("Wrote a flash page.\n"); 
}


//function to load and write program memory
//args: addr is the 12 bit address of the memory location
//      low_data and high_data are the values to write to that location
void load_prog_page(uint16_t addr, uint8_t low_data, uint8_t high_data)//int addr_MSB, 
{
    //load program memory low byte (little endian)
    spi.write(0x40);
    spi.write(0x00);
    spi.write(LSB(addr));
    spi.write(low_data);
    
    //load program memory high byte
    spi.write(0x48);
    spi.write(0x00);
    spi.write(LSB(addr));
    spi.write(high_data);
    //pc.printf(" Wrote: %x %x to LSB address: %x\n", high_data, low_data, LSB(addr));
   
    // write page if 32 words have now been written
    if(addr % MAX_PAGE_SIZE == (MAX_PAGE_SIZE-1))
        write_prog_page(addr);
}

void write_lock_bits(uint8_t bits)
{
    bits = bits & 0xFF;
    spi.write(0xAC);
    spi.write(0xE0);
    spi.write(0x00);
    spi.write(bits);
    still_programming();
    pc.printf("Wrote lock bits...\n");
}

void write_fuse_bits(uint8_t bits)
{
    bits = bits & 0xFF;
    spi.write(0xAC);
    spi.write(0xA0);
    spi.write(0x00);
    spi.write(bits);
    still_programming();
    pc.printf("Wrote fuse bits...\n");
}

void write_fuse_bits_high(uint8_t bits)
{
    bits = bits & 0xFF;
    spi.write(0xAC);
    spi.write(0xA8);
    spi.write(0x00);
    spi.write(bits);
    still_programming();
    pc.printf("Wrote fuse bits high...\n");
}

void write_extended_fuse_bits(uint8_t bits)
{
    bits = bits & 0xFF;
    spi.write(0xAC);
    spi.write(0xA4);
    spi.write(0x00);
    spi.write(bits);
    still_programming();
    pc.printf("Wrote extended fuse bits...\n");
}

uint8_t read_byte(FILE *file)
{
    char ascii_char[2];
    fread(&ascii_char, 1, 2, file);
    return   (((ascii_char[0] < 65) ? (ascii_char[0]-48) : (ascii_char[0]-55)) << 4)
            | ((ascii_char[1] < 65) ? (ascii_char[1]-48) : (ascii_char[1]-55));
}

void read_prog_flash(uint8_t addr_MSB, uint8_t addr_LSB)
{
    spi.write(0x28);
    spi.write(addr_MSB);
    spi.write(addr_LSB);
    pc.printf("At address LSB %x: MSB: %x - %x ",addr_LSB,addr_MSB,spi.write(0x00));
    spi.write(0x20);
    spi.write(addr_MSB);
    spi.write(addr_LSB);
    pc.printf("%x\n",spi.write(0x00));      
}

int main() {
    reset = 1;
    // Setup the spi for 8 bit data,writing data on the rising SCK edge,
    // and reading data on the falling SCK edge as according to AVR specs
    // with a 1MHz clock rate
    pc.printf("\nPress any button to program the AVR.\n");
    char c = pc.getc();
    
    spi.format(8,1);        //SPI format: write data on rising edge, read on falling
                            //w/ a base clock value of zero
    spi.frequency(TARGET_CLK >> 2);
    //wait(0.5);
    pc.printf("SPI interface started...\n");
    
    // Select the device by seting chip select low
    reset = 0;
    wait(0.02); 

    if(enable_prog_mode() != 0)  //Enable programming mode and check for errors
        return -1;
    spi.write(0x30);
    spi.write(0x00);
    spi.write(0x00);
    pc.printf("SIGNATURE BYTE: %x\n",spi.write(0x00));
    chip_erase();
    
    write_lock_bits(0xFF);                  //1111 1111
    write_fuse_bits(0x62);                  //1110 0010
    write_fuse_bits_high(0xDF);             //1101 1111
    write_extended_fuse_bits(0xF9);         //1111 1001
    
    //Opening a file on local FS as in example code
    pc.printf("Opening File...\n"); 
    int flag = 0;
    FILE *hex_file;
    hex_file = fopen("/local/avr","r");
    if(hex_file !=NULL)
    {    
        uint16_t address = 0;
        char temp;
        temp = fgetc(hex_file);
        while(flag == 0)
        {
            if(temp == ':')
            {
                uint8_t length = read_byte(hex_file);
                if(length == 0){
                    flag = 1;
                    printf("EOF line reached.\n");
                }
                else{
                    fseek(hex_file, 6, SEEK_CUR); //2 if reading address
                    
                    for(uint8_t i=0;i<length;i+=2){
                        uint8_t low_data = read_byte(hex_file);
                        uint8_t high_data = read_byte(hex_file);
                       
                        //load data bytes here
                        load_prog_page(address, low_data, high_data);
                        
                        address++;
                    }
                    while((temp = fgetc(hex_file)) != ':');
                    //pc.printf("\n");             
                }
            }
            else flag =1;
        }
        pc.printf("WRITE THE PAGE!\n");//write page here
        write_prog_page(address);
        fclose(hex_file);
    }
    else {
        pc.printf("Failed to open the file...check the name.\n");          
    }
    pc.printf("Successfully programmed!(hopefully...)\n");    
    
    // Deselect the device
    reset = 1;
    wait(0.02);
    return 0;    
}