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
229
230
231
232
233
|
/* 8seg LED display driver firmware
* Copyright (C) 2018 Sebastian Götte <code@jaseg.net>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include "serial.h"
#include "mac.h"
unsigned int uart_overruns = 0;
unsigned int invalid_frames = 0;
static union tx_buf_union tx_buf;
volatile union rx_buf_union rx_buf;
void serial_init() {
USART1->CR1 = /* 8-bit -> M1, M0 clear */
/* RTOIE clear */
(8 << USART_CR1_DEAT_Pos) /* 8 sample cycles/1 bit DE assertion time */
| (8 << USART_CR1_DEDT_Pos) /* 8 sample cycles/1 bit DE assertion time */
/* OVER8 clear. Use default 16x oversampling */
/* CMIF clear */
| USART_CR1_MME
/* WAKE clear */
/* PCE, PS clear */
| USART_CR1_RXNEIE /* Enable receive interrupt */
/* other interrupts clear */
| USART_CR1_TE
| USART_CR1_RE;
/* Invert TX and DE to accomodate the level shifters */
USART1->CR2 = USART_CR2_TXINV;
USART1->CR3 = USART_CR3_DEM | USART_CR3_DEP; /* enable RS485 DE (output on RTS) */
/* Set divider for 9600 baud rate @48MHz system clock. */
int usartdiv = 5000;
USART1->BRR = usartdiv;
/* And... go! */
USART1->CR1 |= USART_CR1_UE;
/* Enable receive interrupt */
NVIC_EnableIRQ(USART1_IRQn);
NVIC_SetPriority(USART1_IRQn, 1);
}
void tx_char(uint8_t c) {
while (!(USART1->ISR & USART_ISR_TC));
USART1->TDR = c;
}
void send_frame_formatted(uint8_t *buf, int len) {
uint8_t *p=buf, *q=buf, *end=buf+len;
do {
while (*q && q!=end)
q++;
tx_char(q-p+1);
while (*p && p!=end)
tx_char(*p++);
p++, q++;
} while (p < end);
tx_char('\0');
}
void send_status_reply(void) {
tx_buf.desc_reply.firmware_version = FIRMWARE_VERSION;
tx_buf.desc_reply.hardware_version = HARDWARE_VERSION;
tx_buf.desc_reply.pad[0] = tx_buf.desc_reply.pad[1] = 0;
tx_buf.desc_reply.uptime_s = sys_time_s;
//tx_buf.desc_reply.vcc_mv = adc_vcc_mv;
//tx_buf.desc_reply.temp_celsius = adc_temp_celsius;
tx_buf.desc_reply.global_brightness = global_brightness;
tx_buf.desc_reply.framerate_millifps = frame_duration_us > 0 ? 1000000000 / frame_duration_us : 0;
tx_buf.desc_reply.uart_overruns = uart_overruns;
tx_buf.desc_reply.invalid_frames = invalid_frames;
send_frame_formatted(tx_buf.byte_data, sizeof(tx_buf.desc_reply));
}
/* This is the higher-level protocol handler for the serial protocol. It gets passed the number of data bytes in this
* frame (which may be zero) and returns a pointer to the buffer where the next frame should be stored.
*/
volatile uint8_t *packet_received(int len) {
static enum {
PROT_ADDRESSED = 0,
PROT_IGNORE = 2,
} protocol_state = PROT_IGNORE;
/* Use mac frames as delimiters to synchronize this protocol layer */
trigger_comm_led();
if (len == 0) { /* Discovery packet */
if (sys_time_tick < 100) { /* Only respond during the first 100ms after boot */
send_frame_formatted((uint8_t*)&device_mac, sizeof(device_mac));
}
} else if (len == 1) { /* Command packet */
if (protocol_state == PROT_ADDRESSED) {
switch (rx_buf.byte_data[0]) {
case 0x01:
send_status_reply();
break;
}
} else {
invalid_frames++;
trigger_error_led();
}
protocol_state = PROT_IGNORE;
} else if (len == 4) { /* Address packet */
if (rx_buf.mac_data == device_mac) { /* we are addressed */
protocol_state = PROT_ADDRESSED; /* start listening for frame buffer data */
} else { /* we are not addressed */
protocol_state = PROT_IGNORE; /* ignore packet */
}
} else if (len == sizeof(rx_buf.set_fb_rq)/2) {
if (protocol_state == PROT_ADDRESSED) { /* First of two half-framebuffer data frames */
/* FIXME */
/* Go to "hang mode" until next zero-length packet. */
protocol_state = PROT_IGNORE;
}
} else {
/* FIXME An invalid packet has been received. What should we do? */
invalid_frames++;
trigger_error_led();
protocol_state = PROT_IGNORE; /* go into "hang mode" until next zero-length packet */
}
/* By default, return rx_buf.byte_data . This means if an invalid protocol state is reached ("hang mode"), the next
* frame is still written to rx_buf. This is not a problem since whatever garbage is written at that point will be
* overwritten before the next buffer transfer. */
return rx_buf.byte_data;
}
void USART1_IRQHandler(void) {
/* Since a large amount of data will be shoved down this UART interface we need a more reliable and more efficient
* way of framing than just waiting between transmissions.
*
* This code uses "Consistent Overhead Byte Stuffing" (COBS). For details, see its Wikipedia page[0] or the proper
* scientific paper[1] published on it. Roughly, it works like this:
*
* * A frame is at most 254 bytes in length.
* * The null byte 0x00 acts as a frame delimiter. There is no null bytes inside frames.
* * Every frame starts with an "overhead" byte indicating the number of non-null payload bytes until the next null
* byte in the payload, **plus one**. This means this byte can never be zero.
* * Every null byte in the payload is replaced by *its* distance to *its* next null byte as above.
*
* This means, at any point the receiver can efficiently be synchronized on the next frame boundary by simply
* waiting for a null byte. After that, only a simple state machine is necessary to strip the overhead byte and a
* counter to then count skip intervals.
*
* Here is Wikipedia's table of example values:
*
* Unencoded data Encoded with COBS
* 00 01 01 00
* 00 00 01 01 01 00
* 11 22 00 33 03 11 22 02 33 00
* 11 22 33 44 05 11 22 33 44 00
* 11 00 00 00 02 11 01 01 01 00
* 01 02 ...FE FF 01 02 ...FE 00
*
* [0] https://en.wikipedia.org/wiki/Consistent_Overhead_Byte_Stuffing
* [1] Cheshire, Stuart; Baker, Mary (1999). "Consistent Overhead Byte Stuffing"
* IEEE/ACM Transactions on Networking. doi:10.1109/90.769765
* http://www.stuartcheshire.org/papers/COBSforToN.pdf
*/
/* This pointer stores where we write data. The higher-level protocol logic decides on a frame-by-frame-basis where
* the next frame's data will be stored. */
static volatile uint8_t *writep = rx_buf.byte_data;
/* Index inside the current frame payload */
static int rxpos = 0;
/* COBS state machine. This implementation might be a little too complicated, but it works well enough and I find it
* reasonably easy to understand. */
static enum {
COBS_WAIT_SYNC = 0, /* Synchronize with frame */
COBS_WAIT_START = 1, /* Await overhead byte */
COBS_RUNNING = 2 /* Process payload */
} cobs_state = 0;
/* COBS skip counter. During payload processing this contains the remaining non-null payload bytes */
static int cobs_count = 0;
if (USART1->ISR & USART_ISR_ORE) { /* Overrun handling */
uart_overruns++;
trigger_error_led();
/* Reset and re-synchronize. Retry next frame. */
rxpos = 0;
cobs_state = COBS_WAIT_SYNC;
/* Clear interrupt flag */
USART1->ICR = USART_ICR_ORECF;
} else { /* Data received */
uint8_t data = USART1->RDR; /* This automatically acknowledges the IRQ */
if (data == 0x00) { /* End-of-packet */
/* Process higher protocol layers on this packet. */
writep = packet_received(rxpos);
/* Reset for next packet. */
cobs_state = COBS_WAIT_START;
rxpos = 0;
} else { /* non-null byte */
if (cobs_state == COBS_WAIT_SYNC) { /* Wait for null byte */
/* ignore data */
} else if (cobs_state == COBS_WAIT_START) { /* Overhead byte */
cobs_count = data;
cobs_state = COBS_RUNNING;
} else { /* Payload byte */
if (--cobs_count == 0) { /* Skip byte */
cobs_count = data;
data = 0;
}
/* Write processed payload byte to current receive buffer */
writep[rxpos++] = data;
}
}
}
}
|
