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scoutos / scout_avr / bom / tiny-twi.c @ 5f7a1707

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1	c4f160ba	Tom Mullins	#include <avr/io.h>
2			#include <avr/interrupt.h>
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
7			#define SCL PB2
8
9	cbe25c0a	tmullins	#define RECV_BUF_SIZE 3
10	b3a1dae4	Tom Mullins	#define SEND_BUF_SIZE 100
11	c4f160ba	Tom Mullins
12			uint8_t address;
13
14	08af0896	Tom Mullins	typedef enum {
15	c4f160ba	Tom Mullins	IDLE,
16			ADDRESS,
17			SEND_READ_ACK,
18			SEND_WRITE_ACK,
19			SEND_DATA,
20			RECV_DATA,
21			RECV_ACK
22	08af0896	Tom Mullins	} state_t;
23	c4f160ba	Tom Mullins
24	08af0896	Tom Mullins	state_t state;
25	c4f160ba	Tom Mullins	uint8_t recv_idx;
26			uint8_t recv_data[RECV_BUF_SIZE];
27	0167b233	Aaron Perley	slave_rx_t onDataRecieved;
28	e4d78d85	Julian Binder	typedef struct {
29	b3a1dae4	Tom Mullins	uint8_t start;
30			uint8_t end;
31			uint8_t data[SEND_BUF_SIZE];
32			bool full;
33	e4d78d85	Julian Binder	} queue;
34
35			queue send_queue;
36	c4f160ba	Tom Mullins
37			static void twi_set_ctr(char n) {
38	797244ed	Aaron Perley	USISR = n;
39	16da2c8f	Tom Mullins	}
40
41	c4f160ba	Tom Mullins	static void twi_ready() {
42	797244ed	Aaron Perley	USISR = _BV(USISIF) \| _BV(USIOIF) \| _BV(USIPF) \| _BV(USIDC);
43			DDRB \|= _BV(SCL); //SCL output
44			DDRB &= ~_BV(SDA); //SDA input
45	c4f160ba	Tom Mullins
46			// enable start condition interrupt
47			USICR \|= _BV(USISIE);
48
49			// disable counter overflow interrupt
50			USICR &= ~_BV(USIOIE);
51
52			state = IDLE;
53			}
54
55			static void twi_start() {
56	797244ed	Aaron Perley	// enable counter overflow interrupt (fires after 8 bits)
57			USICR \|= _BV(USIOIE);
58
59			USISR = _BV(USISIF);
60	c4f160ba	Tom Mullins
61			// zero counter
62			twi_set_ctr(0);
63
64			state = ADDRESS;
65			recv_idx = 0;
66			}
67
68			static void twi_send_ack(char is_read) {
69
70			// set counter to 14
71			twi_set_ctr(14);
72
73			// set SDA low
74			USIDR = 0;
75	797244ed	Aaron Perley	DDRB \|= _BV(SDA);
76	c4f160ba	Tom Mullins
77			// set state
78			state = is_read? SEND_READ_ACK : SEND_WRITE_ACK;
79			}
80
81	240c122b	Tom Mullins	static void twi_send_data() {
82			twi_set_ctr(0);
83	b3a1dae4	Tom Mullins	if (send_queue.start == send_queue.end && !send_queue.full) {
84	5f7a1707	Tom Mullins	USIDR = 0xFF;
85	b3a1dae4	Tom Mullins	} else {
86			USIDR = send_queue.data[send_queue.start++];
87			if (send_queue.start == SEND_BUF_SIZE)
88			send_queue.start = 0;
89			send_queue.full = 0;
90			}
91	240c122b	Tom Mullins	DDRB \|= _BV(SDA);
92			state = SEND_DATA;
93			}
94
95			static void twi_recv_ack() {
96			twi_set_ctr(14);
97			DDRB &= ~_BV(SDA);
98			state = RECV_ACK;
99			}
100
101	c4f160ba	Tom Mullins	ISR(USI_START_vect) {
102			twi_start();
103			}
104
105			ISR(USI_OVF_vect) {
106	6185434e	Tom Mullins	uint8_t input = USIDR; // TODO make sure this is correct
107	c4f160ba	Tom Mullins	switch (state) {
108
109			case IDLE:
110			// shouldn't reach here
111			twi_ready();
112			break;
113
114			case ADDRESS:
115			if (input >> 1 == address) {
116			// send ack
117			twi_send_ack(input & 1);
118			} else {
119			// go back to listening for start condition
120			twi_ready();
121			}
122			break;
123
124			case SEND_WRITE_ACK:
125	6185434e	Tom Mullins	if (recv_idx == RECV_BUF_SIZE) {
126			twi_ready();
127			onDataRecieved(recv_data, RECV_BUF_SIZE);
128			} else {
129			DDRB &= ~_BV(SDA);
130			state = RECV_DATA;
131			}
132	c4f160ba	Tom Mullins	break;
133
134			case RECV_DATA:
135			twi_send_ack(0);
136	6185434e	Tom Mullins	recv_data[recv_idx] = input;
137	c4f160ba	Tom Mullins	recv_idx++;
138			break;
139
140			case SEND_READ_ACK:
141	240c122b	Tom Mullins	twi_send_data();
142	c4f160ba	Tom Mullins	break;
143
144			case SEND_DATA:
145	240c122b	Tom Mullins	twi_recv_ack();
146	c4f160ba	Tom Mullins	break;
147
148			case RECV_ACK:
149	240c122b	Tom Mullins	if (input & 1) {
150			// received nak
151			twi_ready();
152			} else {
153			// received ack
154			twi_send_data();
155			}
156	c4f160ba	Tom Mullins	break;
157			}
158	797244ed	Aaron Perley	USISR = _BV(USIOIF) \| (USISR & 0xF);
159	c4f160ba	Tom Mullins	}
160
161	0167b233	Aaron Perley	void smb_init(slave_rx_t callback) {
162	c4f160ba	Tom Mullins	// TODO do we want USICS0 (3)?
163			USICR = _BV(USIWM1) \| _BV(USIWM0) \| _BV(USICS1);
164	797244ed	Aaron Perley	PORTB \|= _BV(SDA) \| _BV(SCL);
165	c4f160ba	Tom Mullins	twi_ready();
166	0167b233	Aaron Perley	onDataRecieved = callback;
167	c4f160ba	Tom Mullins	}
168
169			void smb_set_address(uint8_t addr) {
170			address = addr;
171			}
172	0167b233	Aaron Perley
173	cbe25c0a	tmullins	void smb_send_data(uint8_t* data, uint8_t length) {
174	b3a1dae4	Tom Mullins	uint8_t i;
175			for (i=0; i<length && !send_queue.full; i++) {
176			send_queue.data[send_queue.end++] = data[i];
177			if (send_queue.end == SEND_BUF_SIZE)
178			send_queue.end = 0;
179			if (send_queue.end == send_queue.start)
180			send_queue.full = 1;
181			}
182			}

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scoutos / scout_avr / bom / tiny-twi.c @ 5f7a1707