blob: 74bcbb6bf6e205e85008bf5b716f59adf6f8e103 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
|
/*
* WARNING: be careful changing this code, it is very timing dependent
*/
#ifndef F_CPU
#define F_CPU 16000000
#endif
#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>
#include <stdbool.h>
#include "serial.h"
#ifndef USE_I2C
// Serial pulse period in microseconds. Its probably a bad idea to lower this
// value.
#define SERIAL_DELAY 24
uint8_t volatile serial_slave_buffer[SERIAL_SLAVE_BUFFER_LENGTH] = {0};
uint8_t volatile serial_master_buffer[SERIAL_MASTER_BUFFER_LENGTH] = {0};
#define SLAVE_DATA_CORRUPT (1<<0)
volatile uint8_t status = 0;
inline static
void serial_delay(void) {
_delay_us(SERIAL_DELAY);
}
inline static
void serial_output(void) {
SERIAL_PIN_DDR |= SERIAL_PIN_MASK;
}
// make the serial pin an input with pull-up resistor
inline static
void serial_input(void) {
SERIAL_PIN_DDR &= ~SERIAL_PIN_MASK;
SERIAL_PIN_PORT |= SERIAL_PIN_MASK;
}
inline static
uint8_t serial_read_pin(void) {
return !!(SERIAL_PIN_INPUT & SERIAL_PIN_MASK);
}
inline static
void serial_low(void) {
SERIAL_PIN_PORT &= ~SERIAL_PIN_MASK;
}
inline static
void serial_high(void) {
SERIAL_PIN_PORT |= SERIAL_PIN_MASK;
}
void serial_master_init(void) {
serial_output();
serial_high();
}
void serial_slave_init(void) {
serial_input();
// Enable INT0
EIMSK |= _BV(INT0);
// Trigger on falling edge of INT0
EICRA &= ~(_BV(ISC00) | _BV(ISC01));
}
// Used by the master to synchronize timing with the slave.
static
void sync_recv(void) {
serial_input();
// This shouldn't hang if the slave disconnects because the
// serial line will float to high if the slave does disconnect.
while (!serial_read_pin());
serial_delay();
}
// Used by the slave to send a synchronization signal to the master.
static
void sync_send(void) {
serial_output();
serial_low();
serial_delay();
serial_high();
}
// Reads a byte from the serial line
static
uint8_t serial_read_byte(void) {
uint8_t byte = 0;
serial_input();
for ( uint8_t i = 0; i < 8; ++i) {
byte = (byte << 1) | serial_read_pin();
serial_delay();
_delay_us(1);
}
return byte;
}
// Sends a byte with MSB ordering
static
void serial_write_byte(uint8_t data) {
uint8_t b = 8;
serial_output();
while( b-- ) {
if(data & (1 << b)) {
serial_high();
} else {
serial_low();
}
serial_delay();
}
}
// interrupt handle to be used by the slave device
ISR(SERIAL_PIN_INTERRUPT) {
sync_send();
uint8_t checksum = 0;
for (int i = 0; i < SERIAL_SLAVE_BUFFER_LENGTH; ++i) {
serial_write_byte(serial_slave_buffer[i]);
sync_send();
checksum += serial_slave_buffer[i];
}
serial_write_byte(checksum);
sync_send();
// wait for the sync to finish sending
serial_delay();
// read the middle of pulses
_delay_us(SERIAL_DELAY/2);
uint8_t checksum_computed = 0;
for (int i = 0; i < SERIAL_MASTER_BUFFER_LENGTH; ++i) {
serial_master_buffer[i] = serial_read_byte();
sync_send();
checksum_computed += serial_master_buffer[i];
}
uint8_t checksum_received = serial_read_byte();
sync_send();
serial_input(); // end transaction
if ( checksum_computed != checksum_received ) {
status |= SLAVE_DATA_CORRUPT;
} else {
status &= ~SLAVE_DATA_CORRUPT;
}
}
inline
bool serial_slave_DATA_CORRUPT(void) {
return status & SLAVE_DATA_CORRUPT;
}
// Copies the serial_slave_buffer to the master and sends the
// serial_master_buffer to the slave.
//
// Returns:
// 0 => no error
// 1 => slave did not respond
int serial_update_buffers(void) {
// this code is very time dependent, so we need to disable interrupts
cli();
// signal to the slave that we want to start a transaction
serial_output();
serial_low();
_delay_us(1);
// wait for the slaves response
serial_input();
serial_high();
_delay_us(SERIAL_DELAY);
// check if the slave is present
if (serial_read_pin()) {
// slave failed to pull the line low, assume not present
sei();
return 1;
}
// if the slave is present syncronize with it
sync_recv();
uint8_t checksum_computed = 0;
// receive data from the slave
for (int i = 0; i < SERIAL_SLAVE_BUFFER_LENGTH; ++i) {
serial_slave_buffer[i] = serial_read_byte();
sync_recv();
checksum_computed += serial_slave_buffer[i];
}
uint8_t checksum_received = serial_read_byte();
sync_recv();
if (checksum_computed != checksum_received) {
sei();
return 1;
}
uint8_t checksum = 0;
// send data to the slave
for (int i = 0; i < SERIAL_MASTER_BUFFER_LENGTH; ++i) {
serial_write_byte(serial_master_buffer[i]);
sync_recv();
checksum += serial_master_buffer[i];
}
serial_write_byte(checksum);
sync_recv();
// always, release the line when not in use
serial_output();
serial_high();
sei();
return 0;
}
#endif
|
