The code for VW Gamma V radio unlock (CD changer emulation)

vwcdc.c

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

//#define pSS   
#define pDATA 0b00001000
#define pCLK  0b00100000


typedef int8_t    INT8;   //char
typedef uint8_t   UINT8;  //unsigned char

typedef int16_t   INT16;  //int
typedef uint16_t  UINT16; //unsigned int

typedef int32_t   INT32;  //long
typedef uint32_t  UINT32; //unsigned long

typedef int64_t   INT64;  //long long
typedef uint64_t  UINT64; //unsigned long long


void send_byte(UINT8 c)
{
  SPDR = c;
  loop_until_bit_is_set(SPSR, SPIF); //wait for transmission complete

  _delay_us(700); //335 700

  return;
}


void send_package(UINT8 c0, UINT8 c1, UINT8 c2, UINT8 c3, UINT8 c4, UINT8 c5, UINT8 c6, UINT8 c7)
{
  send_byte(c0);
  send_byte(c1);
  send_byte(c2);
  send_byte(c3);
  send_byte(c4);
  send_byte(c5);
  send_byte(c6);
  send_byte(c7);

  return;
}


int main(void)
{
  //init ports
  //DDRB = pDATA|pCLK;
  DDRB = 0b00111111; //Port B (pins 13-8) ouputs. first two 0's b/c no pins there
  //PORTB = pDATA|pCLK|pSS;
  PORTB = 0b00111111;

  //analog comparator Off
  ACSR = (1<<ACD);

  //init watchdog timer
  wdt_enable(WDTO_1S);
  wdt_reset();
  
  //init spi
  //SPCR = (1<<SPE)|(1<<MSTR)|(1<<CPOL)|(1<<SPR0); //enable SPI, Master, clock=fcpu/8=8us
  SPCR = (1<<SPE)|(1<<MSTR)|(1<<CPOL)|(1<<SPR0)|(1<<SPR1); //enable SPI, Master, clock=fcpu/8=8us
  SPSR = (1<<SPI2X);

  //send init packages
  _delay_ms(10);
  _delay_ms(10);
  send_package(0x74,0xBE,0xFE,0xFF,0xFF,0xFF,0x8F,0x7C); //idle
  _delay_ms(10);
  send_package(0x34,0xFF,0xFE,0xFE,0xFE,0xFF,0xFA,0x3C); //load disc
  _delay_ms(10);
  send_package(0x74,0xBE,0xFE,0xFF,0xFF,0xFF,0x8F,0x7C); //idle

  for(;;)
  {
    wdt_reset();

    _delay_ms(10);
    //                disc  trk  min  sec
    send_package(0x74,0xBE,0xFE,0xFF,0xFF,0xFF,0xCF,0x7C);
  }
}

vwcdc_arduino.c

#include <SPI.h>
#define CLK_PIN 13
#define DATA_OUT_PIN 11


#define ATTINY 1

#ifdef ATTINY
  #define CLK_PIN 2
  #define DATA_OUT_PIN 1
  
  #include <SoftSPI.h>
  SoftSPI mySPI(DATA_OUT_PIN, 2, CLK_PIN);
  
  #define SPI mySPI
#endif

void setup() {
  pinMode(CLK_PIN, OUTPUT);
  pinMode(DATA_OUT_PIN, OUTPUT);

  SPI.begin();
  SPI.setClockDivider(SPI_CLOCK_DIV16);
  SPI.setDataMode(SPI_MODE2);
  SPI.setBitOrder(MSBFIRST);
}

void send_byte(uint8_t c) {
  SPI.transfer(c);
  delayMicroseconds(700);
}

void send_package(uint8_t c0, uint8_t c1, uint8_t c2, uint8_t c3, uint8_t c4, uint8_t c5, uint8_t c6, uint8_t c7)
{
  send_byte(c0);
  send_byte(c1);
  send_byte(c2);
  send_byte(c3);
  send_byte(c4);
  send_byte(c5);
  send_byte(c6);
  send_byte(c7);
}

void loop() {
  //                disc  trk  min  sec
  send_package(0x74,0xBE,0xFE,0xFF,0xFF,0xFF,0xCF,0x7C);
  delay(10);
}