scoutos / scout_avr / bom / tiny-twi.c @ 5f7a1707
History | View | Annotate | Download (3.32 KB)
1 |
#include <avr/io.h> |
---|---|
2 |
#include <avr/interrupt.h> |
3 |
#include <util/delay.h> |
4 |
#include "tiny-twi.h" |
5 |
|
6 |
#define SDA PB0
|
7 |
#define SCL PB2
|
8 |
|
9 |
#define RECV_BUF_SIZE 3 |
10 |
#define SEND_BUF_SIZE 100 |
11 |
|
12 |
uint8_t address; |
13 |
|
14 |
typedef enum { |
15 |
IDLE, |
16 |
ADDRESS, |
17 |
SEND_READ_ACK, |
18 |
SEND_WRITE_ACK, |
19 |
SEND_DATA, |
20 |
RECV_DATA, |
21 |
RECV_ACK |
22 |
} state_t; |
23 |
|
24 |
state_t state; |
25 |
uint8_t recv_idx; |
26 |
uint8_t recv_data[RECV_BUF_SIZE]; |
27 |
slave_rx_t onDataRecieved; |
28 |
typedef struct { |
29 |
uint8_t start; |
30 |
uint8_t end; |
31 |
uint8_t data[SEND_BUF_SIZE]; |
32 |
bool full;
|
33 |
} queue; |
34 |
|
35 |
queue send_queue; |
36 |
|
37 |
static void twi_set_ctr(char n) { |
38 |
USISR = n; |
39 |
} |
40 |
|
41 |
static void twi_ready() { |
42 |
USISR = _BV(USISIF) | _BV(USIOIF) | _BV(USIPF) | _BV(USIDC); |
43 |
DDRB |= _BV(SCL); //SCL output
|
44 |
DDRB &= ~_BV(SDA); //SDA input
|
45 |
|
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 |
// enable counter overflow interrupt (fires after 8 bits)
|
57 |
USICR |= _BV(USIOIE); |
58 |
|
59 |
USISR = _BV(USISIF); |
60 |
|
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 |
DDRB |= _BV(SDA); |
76 |
|
77 |
// set state
|
78 |
state = is_read? SEND_READ_ACK : SEND_WRITE_ACK; |
79 |
} |
80 |
|
81 |
static void twi_send_data() { |
82 |
twi_set_ctr(0);
|
83 |
if (send_queue.start == send_queue.end && !send_queue.full) {
|
84 |
USIDR = 0xFF;
|
85 |
} 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 |
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 |
ISR(USI_START_vect) { |
102 |
twi_start(); |
103 |
} |
104 |
|
105 |
ISR(USI_OVF_vect) { |
106 |
uint8_t input = USIDR; // TODO make sure this is correct
|
107 |
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 |
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 |
break;
|
133 |
|
134 |
case RECV_DATA:
|
135 |
twi_send_ack(0);
|
136 |
recv_data[recv_idx] = input; |
137 |
recv_idx++; |
138 |
break;
|
139 |
|
140 |
case SEND_READ_ACK:
|
141 |
twi_send_data(); |
142 |
break;
|
143 |
|
144 |
case SEND_DATA:
|
145 |
twi_recv_ack(); |
146 |
break;
|
147 |
|
148 |
case RECV_ACK:
|
149 |
if (input & 1) { |
150 |
// received nak
|
151 |
twi_ready(); |
152 |
} else {
|
153 |
// received ack
|
154 |
twi_send_data(); |
155 |
} |
156 |
break;
|
157 |
} |
158 |
USISR = _BV(USIOIF) | (USISR & 0xF);
|
159 |
} |
160 |
|
161 |
void smb_init(slave_rx_t callback) {
|
162 |
// TODO do we want USICS0 (3)?
|
163 |
USICR = _BV(USIWM1) | _BV(USIWM0) | _BV(USICS1); |
164 |
PORTB |= _BV(SDA) | _BV(SCL); |
165 |
twi_ready(); |
166 |
onDataRecieved = callback; |
167 |
} |
168 |
|
169 |
void smb_set_address(uint8_t addr) {
|
170 |
address = addr; |
171 |
} |
172 |
|
173 |
void smb_send_data(uint8_t* data, uint8_t length) {
|
174 |
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 |
} |