[AVR] Getting garbage data from external eeprom on STK600

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#include <asf.h>
 
//Slave select low
 
#define cs_low() \
delay_us(10);\
PORTB=(0<<PB0);\
delay_us(10);
 
//Slave select high
 
#define cs_high() \
delay_us(10);\
PORTB=(1<<PB0);\
delay_us(10);
 
 
 
char opcode_cnt=0;               //Counts number bytes required before start reading actual data  
unsigned char data;              //Variable to save save received data
volatile char rd_cmplete_flg=0;  //Flag is set after read operation completed
int pg_addr;                     //Indicates address of page
int buff_addr;                   //Indicates starting address of buffer
volatile unsigned int i=0;       //Counts number bytes read
char pwm_init_flg=0;             //Used only once in init_pwm() function
char sample_count=4;
unsigned char continuous_rd_flg=0,status_rd_flg=0;      //continuous_rd_flg to trigger data read in ISR and status_rd_flg to trigger status register read
 
 
void init_pwm(void);
void spimstr_init(void);
void spi_tx(unsigned char byte);
void spi_tx_ISR(unsigned char byte);
unsigned char spi_rx_ISR(void);
unsigned char spi_rx(void);
unsigned char get_status(void);
void init_uart(void);
void continuous_pg_read(unsigned int page_address,unsigned int buffer_address);
 
 
 
int main (void)
{
    // Insert system clock initialization code here (sysclk_init()).
 
    board_init();
    
    init_uart();
    
    spimstr_init();
    
    continuous_pg_read(0x00,0x00);
    
    while(1)
   {
      if(rd_cmplete_flg)
     {
       rd_cmplete_flg=0;     
       
       init_pwm();
     } 
      
      if(i>=23923)
     {
       break;
     } 
   }
    
    // Insert application code here, after the board has been initialized.
}
 
 
 
 
void init_pwm()
{
  if(!pwm_init_flg)
 { 
  pwm_init_flg=0;
 
  DDRB = (1<<PB5);                          // set OC1A as output
 
  TCCR1A = (1<<COM1A1)|(1<<COM1A0)|(1<<WGM10);// set OC1A on compare match, clear OC1A at bottom
     // 8 bit fast PWM
  TCCR1B = (1<<WGM12)|(1<<CS10);                // 8bit fast PWM and clock=8Mhz
 }
 
  TIMSK1 |= (1<<TOIE1);                         // enable timer 1 overflow interrupt
}
 
 
 
void spimstr_init()
{
    //Master Mode Selected
    //MSB out first
    //Clock Polarity and Clock Phase selected as 1
    //Clock Frequency 8MHz/128 selected
 
    SPCR|=(1<<SPE)|(0<<DORD)|(1<<MSTR)|(1<<CPOL)|(1<<CPHA)|(0<<SPR1)|(0<<SPR0);
    
    SPSR=(1<<SPI2X);
}
 
 
 
 
void spi_tx(unsigned char byte)
{
    SPDR=byte;
    
    while(!(SPSR&(1<<SPIF)));        //wait until transmission is completed
}
 
 
 
void spi_tx_ISR(unsigned char byte)
{
    SPDR=byte;
}
 
 
 
unsigned char spi_rx()
{
    while(!(SPSR&(1<<SPIF)));        //wait until reception is completed
    
    return SPDR;
}
 
 
unsigned char spi_rx_ISR()
{
    return SPDR;
}
 
 
 
 
unsigned char get_status()
{
    unsigned char status;
    
    //high to low transition made on SS
    
    cs_low();
    
    spi_tx(0xd7);            //opcode to read status register of EEPROM
    
    status=spi_rx();         //Received the value of status register of EEPROM
    
    status=status & 0x80;
 
    //low to high transition made on SS
    
    cs_high();
    
    return status;
}
 
 
void init_uart()
{
    UBRR1H=0x00;
 
    UBRR1L=0x0c;
    
    UCSR1B|=(1<<RXEN1)|(1<<TXEN1);
    
    UCSR1C|=(1<<UCSZ11)|(1<<UCSZ10);
}
 
 
void continuous_pg_read(unsigned int page_address,unsigned int buffer_address)
{
    pg_addr=page_address;
    
    buff_addr=buffer_address;
    
    while(get_status()==0x00);
    
    cs_low();
    
    spi_tx(0xe8);                           //opcode to read page
    
    SREG=0x80;
    
    SPCR|=(1<<SPIE);
}
 
 
//ISR for Continuous Array Read mode
 
ISR(SPI_STC_vect)
{
  //PORTA=0xff;                            //LED port to ensure the working of interrupt
  
  //delay_ms(1500);
  
  if(!continuous_rd_flg)
 { 
      opcode_cnt++;
  
     switch(opcode_cnt)
    {
       case 1:
      
              spi_tx_ISR((0x00)|(pg_addr>>7));
    
              break;
    
       case 2:
     
              spi_tx_ISR((pg_addr<<1)|(buff_addr>>8));
    
              break;
    
       case 3:
             
              spi_tx_ISR(buff_addr & 0x00ff);
    
              break;
    
       case 4:
      
              spi_tx_ISR(0x00);
    
              break;
    
       case 5:
      
              spi_tx_ISR(0x00);
    
              break;
    
       case 6:
      
              spi_tx_ISR(0x00);
    
              break;
    
       case 7:
      
              spi_tx_ISR(0x00);
    
              break;
      
       case 8:
    
              spi_tx_ISR(0x00);
      
              break;   
  }
 
 
      if(opcode_cnt>=9)
     {
              opcode_cnt=0;                //Reset to zero to repeat switch case
     
              if(rd_cmplete_flg==0)
             {
                    data=spi_rx_ISR();
        
                    rd_cmplete_flg=1;
             }
              //Important Note
     
              //The buffer address and page address has to be incremented before cs_high() only then only this mode works
     
              if(buff_addr<263)            
             {
                    buff_addr++;
             }
      
              else
             {
                    buff_addr=0;         
     
                    pg_addr++;
             }
     
              cs_high();
             
              continuous_rd_flg=1;
     }
 }
  if(status_rd_flg)
 {
      unsigned char status;
    
      status=spi_rx_ISR();  
      
      status=status & 0x80;        
      
      cs_high();
      
      status_rd_flg=0;
      
      continuous_rd_flg=0;
      
      cs_low();
      
      spi_tx_ISR(0xe8);                 //Resend continuous read opcode to read next byte 
 }
 
 //PORTA=~PORTA;
 
 //delay_ms(1500);
}
 
 
ISR(TIMER1_OVF_vect)
{
  //PORTA=0x55;                //LED port to ensure the working of interrupt
  
  //delay_ms(1500);
  
  sample_count--;
 
  if(sample_count==0)
 {
   sample_count=4;
   
   TIMSK1=(0<<TOIE1); 
   
   UDR1=data;
   
   while(!(UCSR1A & (1<<UDRE1)));
   
   i++;
   
   status_rd_flg=1;
   
   cs_low();
   
   spi_tx_ISR(0xd7);       //Send opcode to read status register 
}   
 
  //PORTA=~PORTA;
  
  //delay_ms(1500);
}
 
 
 
void board_init(void)
{
 DDRA|=0xff;                          //optput port for LED
  
 DDRB|=(1<<DDB2)|(1<<DDB1)|(1<<DDB0);     //Direction of SS,MISO,SCK,MOSI pin selected
}