root / scout_avr / bom / tiny-twi.c @ 797244ed
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| 1 | c4f160ba | Tom Mullins | #include <avr/io.h> |
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| 2 | #include <avr/interrupt.h> |
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| 3 | 0167b233 | Aaron Perley | #include <util/delay.h> |
| 4 | 08af0896 | Tom Mullins | #include "tiny-twi.h" |
| 5 | c4f160ba | Tom Mullins | |
| 6 | 797244ed | Aaron Perley | #define SDA PB0
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| 7 | #define SCL PB2
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| 8 | |||
| 9 | c4f160ba | Tom Mullins | #define RECV_BUF_SIZE 2 |
| 10 | |||
| 11 | uint8_t address; |
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| 12 | |||
| 13 | 08af0896 | Tom Mullins | typedef enum { |
| 14 | c4f160ba | Tom Mullins | IDLE, |
| 15 | ADDRESS, |
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| 16 | SEND_READ_ACK, |
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| 17 | SEND_WRITE_ACK, |
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| 18 | SEND_DATA, |
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| 19 | RECV_DATA, |
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| 20 | RECV_ACK |
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| 21 | 08af0896 | Tom Mullins | } state_t; |
| 22 | c4f160ba | Tom Mullins | |
| 23 | 08af0896 | Tom Mullins | state_t state; |
| 24 | c4f160ba | Tom Mullins | uint8_t recv_idx; |
| 25 | uint8_t recv_data[RECV_BUF_SIZE]; |
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| 26 | 0167b233 | Aaron Perley | slave_rx_t onDataRecieved; |
| 27 | c4f160ba | Tom Mullins | |
| 28 | static void twi_set_ctr(char n) { |
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| 29 | 797244ed | Aaron Perley | USISR = n; |
| 30 | 16da2c8f | Tom Mullins | } |
| 31 | |||
| 32 | c4f160ba | Tom Mullins | static void twi_ready() { |
| 33 | 797244ed | Aaron Perley | USISR = _BV(USISIF) | _BV(USIOIF) | _BV(USIPF) | _BV(USIDC); |
| 34 | DDRB |= _BV(SCL); //SCL output
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| 35 | DDRB &= ~_BV(SDA); //SDA input
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| 36 | c4f160ba | Tom Mullins | |
| 37 | // enable start condition interrupt
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| 38 | USICR |= _BV(USISIE); |
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| 39 | |||
| 40 | // disable counter overflow interrupt
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| 41 | USICR &= ~_BV(USIOIE); |
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| 42 | |||
| 43 | state = IDLE; |
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| 44 | } |
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| 45 | |||
| 46 | static void twi_start() { |
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| 47 | 797244ed | Aaron Perley | // enable counter overflow interrupt (fires after 8 bits)
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| 48 | USICR |= _BV(USIOIE); |
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| 49 | |||
| 50 | USISR = _BV(USISIF); |
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| 51 | c4f160ba | Tom Mullins | |
| 52 | // zero counter
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| 53 | twi_set_ctr(0);
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| 54 | |||
| 55 | state = ADDRESS; |
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| 56 | recv_idx = 0;
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| 57 | } |
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| 58 | |||
| 59 | static void twi_send_ack(char is_read) { |
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| 60 | |||
| 61 | // set counter to 14
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| 62 | twi_set_ctr(14);
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| 63 | |||
| 64 | // set SDA low
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| 65 | USIDR = 0;
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| 66 | 797244ed | Aaron Perley | DDRB |= _BV(SDA); |
| 67 | c4f160ba | Tom Mullins | |
| 68 | // set state
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| 69 | state = is_read? SEND_READ_ACK : SEND_WRITE_ACK; |
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| 70 | } |
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| 71 | |||
| 72 | ISR(USI_START_vect) {
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| 73 | 797244ed | Aaron Perley | PORTB |= _BV(PB4); // DEBUG: LED ON
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| 74 | c4f160ba | Tom Mullins | twi_start(); |
| 75 | } |
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| 76 | |||
| 77 | ISR(USI_OVF_vect) {
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| 78 | uint8_t input = USIBR; |
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| 79 | switch (state) {
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| 80 | |||
| 81 | case IDLE:
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| 82 | // shouldn't reach here
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| 83 | twi_ready(); |
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| 84 | break;
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| 85 | |||
| 86 | case ADDRESS:
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| 87 | if (input >> 1 == address) { |
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| 88 | // send ack
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| 89 | twi_send_ack(input & 1);
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| 90 | } else {
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| 91 | // go back to listening for start condition
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| 92 | twi_ready(); |
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| 93 | } |
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| 94 | break;
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| 95 | |||
| 96 | case SEND_WRITE_ACK:
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| 97 | 797244ed | Aaron Perley | DDRB &= ~_BV(SDA); |
| 98 | c4f160ba | Tom Mullins | state = RECV_DATA; |
| 99 | break;
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| 100 | |||
| 101 | case RECV_DATA:
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| 102 | twi_send_ack(0);
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| 103 | recv_data[recv_idx] = USIBR; |
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| 104 | recv_idx++; |
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| 105 | if (recv_idx == RECV_BUF_SIZE) {
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| 106 | twi_ready(); |
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| 107 | 0167b233 | Aaron Perley | onDataRecieved(recv_data, RECV_BUF_SIZE); |
| 108 | c4f160ba | Tom Mullins | } |
| 109 | break;
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| 110 | |||
| 111 | case SEND_READ_ACK:
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| 112 | 797244ed | Aaron Perley | DDRB &= ~_BV(SDA); |
| 113 | c4f160ba | Tom Mullins | // TODO write to USIDR
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| 114 | state = SEND_DATA; |
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| 115 | break;
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| 116 | |||
| 117 | case SEND_DATA:
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| 118 | break;
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| 119 | |||
| 120 | case RECV_ACK:
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| 121 | break;
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| 122 | } |
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| 123 | 797244ed | Aaron Perley | USISR = _BV(USIOIF) | (USISR & 0xF);
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| 124 | c4f160ba | Tom Mullins | } |
| 125 | |||
| 126 | 0167b233 | Aaron Perley | void smb_init(slave_rx_t callback) {
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| 127 | c4f160ba | Tom Mullins | // TODO do we want USICS0 (3)?
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| 128 | USICR = _BV(USIWM1) | _BV(USIWM0) | _BV(USICS1); |
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| 129 | 797244ed | Aaron Perley | PORTB |= _BV(SDA) | _BV(SCL); |
| 130 | c4f160ba | Tom Mullins | twi_ready(); |
| 131 | 0167b233 | Aaron Perley | onDataRecieved = callback; |
| 132 | c4f160ba | Tom Mullins | } |
| 133 | |||
| 134 | void smb_set_address(uint8_t addr) {
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| 135 | address = addr; |
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| 136 | } |
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| 137 | 0167b233 | Aaron Perley | |
| 138 | void testCB(uint8_t* data, int length) { |
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| 139 | PORTB |= _BV(PB4); |
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| 140 | if (data[0]) |
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| 141 | _delay_ms(1000);
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| 142 | else
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| 143 | _delay_ms(500);
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| 144 | PORTB &= ~_BV(PB4); |
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| 145 | } |
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| 146 | |||
| 147 | |||
| 148 | int main() {
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| 149 | 797244ed | Aaron Perley | sei(); |
| 150 | 0167b233 | Aaron Perley | smb_set_address(5);
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| 151 | DDRB |= _BV(DDB4); |
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| 152 | smb_init(testCB); |
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| 153 | 797244ed | Aaron Perley | while(1); |
| 154 | } |