/*
SLdt  220912           Disclaimer: none. Sue me.
MCP23S17 einfachst: 'Blinken' auf GPIO-A
*/

#define F_CPU 16000000UL
#include "util/delay.h"
#include "avr/io.h"

//                  ATmega48PA   ATtiny841
#define SPI_DDR     DDRB       //  DDRA
#define SPI_PORT    PORTB      //  PORTA
#define SCK         PB5        //  PA4
#define MISO        PB4        //  PA5
#define MOSI        PB3        //  PA6
#define SS          PB2        //  A7

#define MCP_OPC     0x40 
#define IODIRA      0x00
#define GPIOA       0x12
#define MCP_DDR     SPI_DDR
#define MCP_PORT    SPI_PORT


void spi_transfer(uint8_t data)
  {
  SPDR = data;            
  while(!(SPSR & (1<<SPIF)));
  }

  void mcp_write(uint8_t addr, uint8_t reg, uint8_t data)
  {
  MCP_PORT &= ~(1<<SS);
  spi_transfer(addr);
  spi_transfer(reg);
  spi_transfer(data);
  MCP_PORT |= (1<<SS);
  }

void mcp_init(uint8_t addr)
  {
  mcp_write(addr, IODIRA, 0x00);  // Port A auf Ausgang
  }

void spi_master_init(void)
  {
  SPI_PORT = 0xFF;
  SPI_DDR  = (1<<SS) | (1<<MOSI) | (1<<SCK);
  SPCR     = (1<<SPE) | (1<<MSTR);
  }
  
  
int main(void)
  {
  spi_master_init();
  mcp_init(MCP_OPC);
  while (1)
    {
    mcp_write(MCP_OPC, GPIOA, 0xFF);
    _delay_ms(200);  
    mcp_write(MCP_OPC, GPIOA, 0x00);
    _delay_ms(500);  
    }
  }