89 lines
2.2 KiB
C
89 lines
2.2 KiB
C
#include <avr/interrupt.h>
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#include <util/delay.h>
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#include <spi.h>
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#define FLASH_LED_COMMAND 0x01
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#define OTHER_SELECT_PIN PB6
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#define SELECT_OTHER PORTB &= ~(1<<OTHER_SELECT_PIN)
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#define DESELECT_OTHER PORTB |= (1<<OTHER_SELECT_PIN)
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#define BUFSIZE 20
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volatile unsigned char incoming[BUFSIZE];
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volatile short int received=0;
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// flash led that's connected to pin PD7
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void flash_led(int count)
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{
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DDRD |= (1<<PD7);
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for (int i=0; i<count*2; i++) {
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PORTD ^= (1<<PD7);
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_delay_ms(75);
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}
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}
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// send a SPI message to the other device - 3 bytes then go back into
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// slave mode
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void send_message()
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{
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setup_spi(SPI_MODE_1, SPI_MSB, SPI_NO_INTERRUPT, SPI_MSTR_CLK8);
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if (SPCR & (1<<MSTR)) { // if we are still in master mode
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SELECT_OTHER; // tell other device to flash LED twice
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send_spi(FLASH_LED_COMMAND); send_spi(0x02); send_spi(0x00);
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DESELECT_OTHER;
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}
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setup_spi(SPI_MODE_1, SPI_MSB, SPI_INTERRUPT, SPI_SLAVE);
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}
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// called when the button pushed and pin INT0 goes from 1 to 0
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ISR(INT0_vect)
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{
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send_message();
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_delay_ms(500); // 'debounce'
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}
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// parse the data received from the other device
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// currently just knows about the FLASH_LED_COMMAND
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void parse_message()
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{
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switch(incoming[0]) {
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case FLASH_LED_COMMAND:
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flash_led(incoming[1]);
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break;
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default:
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flash_led(20);
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}
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}
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// called by the SPI system when there is data ready.
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// Just store the incoming data in a buffer, when we receive a
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// terminating byte (0x00) call parse_message to process the data received
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ISR(SPI_STC_vect)
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{
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incoming[received++] = received_from_spi(0x00);
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if (received >= BUFSIZE || incoming[received-1] == 0x00) {
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parse_message();
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received = 0;
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}
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}
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int main(void)
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{
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// make sure other device is unselected (pin is HIGH) and setup spi
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DESELECT_OTHER;
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DDRB |= (1<<OTHER_SELECT_PIN);
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setup_spi(SPI_MODE_1, SPI_MSB, SPI_INTERRUPT, SPI_SLAVE);
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// raise interrupt when the button is pushed and INT0 pin goes
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// from 1 to 0 (pin PD0 at AT90usbXXX, pin PD2 on ATmegaXXX,
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// arduino pin 2)). The code in ISR(INT0_vect) above will be called
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EICRB = (1<<ISC01) | (0<<ISC00);
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EIMSK |= (1<<INT0);
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sei();
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// flash LED at start to indicate were ready
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flash_led(1);
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while (1); // do nothing
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}
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