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
|
/*
* Copyright © 2012 Keith Packard <keithp@keithp.com>
*
* 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; version 2 of the License.
*
* 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, write to the Free Software Foundation, Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
*/
#include <ao.h>
#include <ao_async.h>
#define AO_ASYNC_BAUD 38400l
#define AO_ASYNC_DELAY (uint8_t) (1000000l / AO_ASYNC_BAUD)
#define LED_PORT PORTB
void
ao_async_start(void)
{
LED_PORT |= (1 << AO_LED_SERIAL);
}
void
ao_async_stop(void)
{
LED_PORT &= ~(1 << AO_LED_SERIAL);
}
void
ao_async_byte(uint8_t byte)
{
uint8_t b;
uint16_t w;
uint8_t v;
uint8_t bit;
uint8_t w_hi, w_lo;
/* start data stop */
w = (0x000 << 0) | (byte << 1) | (0x001 << 9);
w_hi = w >> 8;
w_lo = w;
ao_arch_block_interrupts();
/* Ok, this is a bit painful.
* We need this loop to be precisely timed, which
* means knowing exactly how many instructions will
* be executed for each bit. It's easy to do that by
* compiling the C code and looking at the output,
* but we need this code to work even if the compiler
* changes. So, just hand-code the whole thing
*/
asm volatile (
" ldi %[b], 10\n" // loop value
"loop:\n"
" in %[v], %[port]\n" // read current value
" andi %[v], %[led_mask]\n" // mask to clear LED bit
" mov %[bit], %[w_lo]\n" // get current data byte
" andi %[bit], 0x01\n" // get current data bit
#if AO_LED_SERIAL >= 1
" add %[bit],%[bit]\n" // shift by one
#else
" nop\n"
#endif
#if AO_LED_SERIAL >= 2
" add %[bit],%[bit]\n" // shift by one
#else
" nop\n"
#endif
#if AO_LED_SERIAL >= 3
" add %[bit],%[bit]\n" // shift by one
#else
" nop\n"
#endif
#if AO_LED_SERIAL >= 4
" add %[bit],%[bit]\n" // shift by one
#else
" nop\n"
#endif
#if AO_LED_SERIAL >= 5
" add %[bit],%[bit]\n" // shift by one
#else
" nop\n"
#endif
#if AO_LED_SERIAL >= 6
" add %[bit],%[bit]\n" // shift by one
#else
" nop\n"
#endif
#if AO_LED_SERIAL >= 7
" add %[bit],%[bit]\n" // shift by one
#else
" nop\n"
#endif
" or %[v], %[bit]\n" // add to register
" out %[port], %[v]\n" // write current value
" lsr %[w_hi]\n" // shift data
" ror %[w_lo]\n" // ...
" nop\n"
" nop\n"
" nop\n"
" nop\n"
" nop\n"
" nop\n"
" nop\n"
" nop\n"
" subi %[b], 1\n" // decrement bit count
" brne loop\n" // jump back to top
: [v] "=&r" (v),
[bit] "=&r" (bit),
[b] "=&r" (b),
[w_lo] "+r" (w_lo),
[w_hi] "+r" (w_hi)
: [port] "I" (_SFR_IO_ADDR(LED_PORT)),
[led_mask] "M" ((~(1 << AO_LED_SERIAL)) & 0xff)
);
#if 0
/*
* Here's the equivalent C code to document
* what the above assembly code does
*/
for (b = 0; b < 10; b++) {
uint8_t v = LED_PORT & ~(1 << AO_LED_SERIAL);
v |= (w & 1) << AO_LED_SERIAL;
LED_PORT = v;
w >>= 1;
/* Carefully timed to hit around 9600 baud */
asm volatile ("nop");
asm volatile ("nop");
asm volatile ("nop");
asm volatile ("nop");
asm volatile ("nop");
asm volatile ("nop");
asm volatile ("nop");
asm volatile ("nop");
asm volatile ("nop");
asm volatile ("nop");
asm volatile ("nop");
asm volatile ("nop");
asm volatile ("nop");
}
#endif
ao_arch_release_interrupts();
}
|
