source: avrstuff/V-USB_Dev/firmwares/herePic/main.c@ 8659a17

/* This project is targetted at the VUSBDev hacking board. */

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/wdt.h>
#include <avr/pgmspace.h>
#include <util/delay.h>

#include <string.h>
#include <stdbool.h>

#include "usbdrv/usbdrv.h"
#include "shared.h"

// IO pins:
// PIC <> AVR
// PGC    PB3
// PGD    PB2
// PGM    PB1
// VPP    PB0
// VDD    VCC
// VSS    GND
#define PGC 8
#define PGD 4
#define PGM 2
#define VPP 1


// TODO is it wise to use a timer or two for bit patterns generation ? (see
// CrO2 architecture)
//
// As usual the SPI, TWI and USART are not useable, because we need 6 and 16 bit
// communcations in the ICSP protocol. So we are bit banging bhe ICSP protocol.
// Timers may make it easier to do that in parallel with the USB handling, since
// timings are in the nanosecond range.


uint8_t command;
uint16_t ICSP_data;


int main() {
        // Init
        wdt_enable(WDTO_2S);

        // USB
        usbInit();
        sei();

        // Enter Low Voltage ICSP mode on the PIC
        PORTB &= ~(VPP|PGM|PGD|PGC); // Start with all pin low
        DDRB |= VPP|PGM|PGD|PGC;        // set them as outputs
        _delay_us(4); // Wait for some time
        PORTB |= PGM; // Enable low voltage programming
        PORTB |= VPP; // Enter programming mode

        while(1) {
                wdt_reset();
                usbPoll();
        }
}


void ICSP_command(uint8_t cmd)
{
        for(int i = 6; --i>= 0;)
        {
                PORTB |= PGC;
                if(cmd & 1)
                        PORTB |= PGD;
                else
                        PORTB &= ~PGD;
                PORTB &= ~PGC;

                cmd >>= 1;
        }

        _delay_us(1);
}


void ICSP_write(uint8_t cmd, uint16_t data)
{
        ICSP_command(cmd);

        // send data
        for(int i = 16; --i>= 0;)
        {
                PORTB |= PGC;
                if(data & 1)
                        PORTB |= PGD;
                else
                        PORTB &= ~PGD;
                PORTB &= ~PGC;

                data >>= 1;
        }
        _delay_us(1);
}


void ICSP_read(uint8_t cmd, uint16_t *const data)
{
        ICSP_command(cmd);

        // get data
        for(int i = 16; --i>= 0;)
        {
                PORTB |= PGC;
                *data |= (PORTB & PGD) / PGD;
                PORTB &= ~PGC;

                *data <<= 1;
        }
        _delay_us(1);
}


uint8_t usbFunctionSetup(uint8_t data[8]) {
        usbRequest_t *rq = (void *)data;

        switch(rq->bRequest)
        {
                /* HOST to DEVICE data transfers requests */
                case LoadConfigWord:
                case LoadCodeWord:
                case LoadDataWord:
                {
                        // TODO check there is only and exactly 16 bits of data

                        /* Read the 16-bit data */
                        ICSP_data = (rq->wValue.bytes[0] << 8) | rq->wValue.bytes[0];
                        command = rq->bRequest;

                        // send the command and data
                        ICSP_write(command, ICSP_data);

                        // Return the number of bytes we wrote (none here)
                        return 0;
                }

                /* CONFIGURATION commands (no data is transferred) */
                case NextAddress:
                case BeginEraseProgram:
                case BeginProgramOnly:
                case BulkEraseCode:
                case BulkEraseData:
                case BulkEraseConfig1:
                case BulkEraseConfig2:
                {
                        command = rq->bRequest;

                        // send the command
                        ICSP_command(command);

                        return 0; 
                }

                /* DEVICE to HOST data transfers requests */
                case ReadCodeWord:
                case ReadDataWord:
                {
                        command = rq->bRequest;
                        // TODO send the command and get the result
                        ICSP_read(command, &ICSP_data);
                        usbMsgPtr = (uint8_t*)&ICSP_data;

                        return 2; // We send 2 bytes back
                }
        }
        return 0;
}