// bar_graph_simple.c 
// R. Traylor
// 10.22.13
// demos SPI

// Every half second, a new data led is lit on the bargraph display via SPI
// in a climbing pattern. 

// Expected Connections:
// Bargraph board       LED board or mega128
// --------------       --------------------     
//     reglck           PORTB bit 0 (SS_n)                       
//     srclk            PORTB bit 1 (sclk)
//     sdin             PORTB bit 2 (mosi)
//     oe_n                   ground  (short to gnd2)
//     gnd2                   ground
//     vdd2                     vcc
//     sd_out               no connect

#include <avr/io.h>
#include <util/delay.h>

//***********************************************************************
//                            spi_init                               
// Initalizes the SPI port on the mega128. Does not do any further   
// external device specific initalizations.  Sets up SPI to be:                        
// master mode, clock=clk/2, cycle half phase, low polarity, MSB first
// interrupts disabled, poll SPIF bit in SPSR to check xmit completion
//**********************************************************************
void spi_init(void){
  DDRB  = 0x07;                 //Turn on SS, MOSI, SCLK
  SPCR  = (1<<SPE) | (1<<MSTR); //set up SPI mode
  SPSR  = (1<<SPI2X);           // double speed operation
 }//spi_init


//**********************************************************************
//                                main                                 
//**********************************************************************
int main(){     

uint8_t display_count = 0x01; //holds count for display 
uint8_t i; //dummy counter

//do initialization
spi_init();  //initalize SPI port

while(1){                             //main while loop
    SPDR = display_count;             //send to display 
    while (bit_is_clear(SPSR,SPIF)){} //wait till data sent out
    PORTB |=   0x01;                  //rising edge to regclk on HC595 
    PORTB &= ~(0x01);                 //falling edge
    display_count = (display_count << 1); //shift for next time 
    if(display_count==0x00){display_count=0x01;} //display back to 1st positon
    for(i=0; i<=4; i++){_delay_ms(100);} //0.5 sec delay
  } //while(1)
} //main