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
|
#include <unistd.h>
#include <string.h>
#include "transpose.h"
/* This file contains conversion routines that pre-format the brightness data
* received from the UART such that the interrupt service routines only need to
* push it out the SPI without further computation, making these ISRs nice and
* tight.
*
* To understand this code note the multiplexing scheme used on the board. The
* circuit contains two MBI5026 shift-register LED drivers of 16 channels each
* cascaded. Effectively this behaves like a 32-channel LED driver fed data
* serially. Each output is connected to a single digit's COM pin. All digit's
* segment anode pins are connected together in a large bus fed by one of the
* two auxiliary shift registers.
*
* The firmware is selecting each segment in turn with a full BCM cycle for each
* segment before the next one is selected.
*/
/* This array maps the 32 adressable digits on a board to the 32 bits shifted
* out to the LED drivers. */
uint8_t digit_map[33] = {
0, 1, 2, 3, 28,29,30,31,
4, 5, 6, 7, 24,25,26,27,
8, 9,10,11, 20,21,22,23,
12,13,14,15, 16,17,18,19
};
/* This function produces a 10-bit output buffer ready for the modulation ISRs
* from 10-bit input data encoded for the UART. For the precise data format, see
* transpose.h.
*
* On the UART side we have digits in the order defined in digit_map, 10 byte
* per digit. The first 8 bytes are the 8 LSBs of each segments brightness value
* in the order [A, B, C, D, E, F, G, DECIMAL_POINT]. The two MSBs to make each
* value 10-bit are bit-packed into the remaining two bytes in big-endian byte
* order starting from DP.
*
* On the display frame buffer side, data is stored in multiplexing order:
* first digits, then time/bits and finally segments. So for each segment you
* have a large buffer containing all the bit periods and digits, and for each
* bit period you have 32 bits for all 32 digits.
*/
void transpose_data(volatile uint8_t *rx_buf, volatile struct framebuf *out_fb)
{
/* FIXME this can probably be removed. */
memset((uint8_t *)out_fb, 0, sizeof(*out_fb));
/* 8 MSB loop */
struct data_format *rxp = (struct data_format *)rx_buf;
for (int bit=0; bit<8; bit++) { /* bits */
uint32_t bit_mask = 1U<<bit;
volatile uint32_t *frame_data = out_fb->frame[bit+2].data;
uint8_t *start_inp = rxp->high;
for (volatile uint32_t *outp=frame_data; outp<frame_data+8; outp++) { /* segments */
uint32_t acc = 0;
uint8_t *inp = start_inp++;
for (int digit=0; digit<32; digit++) {
acc |= (*inp & bit_mask) >> bit << digit_map[digit];
inp += sizeof(struct data_format);
}
*outp = acc;
}
}
/* 2 packed LSB loop */
for (int bit=0; bit<2; bit++) { /* bits */
volatile uint32_t *frame_data = out_fb->frame[bit].data;
for (int seg=0; seg<8; seg++) { /* segments */
uint16_t *inp = &rxp->low;
uint32_t mask = 1 << bit << (seg*2);
uint32_t acc = 0;
for (int digit=0; digit<32; digit++) {
acc |= (*inp & mask) >> bit >> (seg*2) << digit_map[digit];
inp += sizeof(struct data_format)/sizeof(uint16_t);
}
frame_data[seg] = acc;
}
}
/* Global analog brightness value */
out_fb->brightness = ((volatile struct framebuf *)rx_buf)->brightness;
}
/* This function was used for testing transpose_data. It does precisely the
* reverse operation. */
void untranspose_data(struct framebuf *fb, uint8_t *txbuf) {
memset(txbuf, 0, sizeof(*fb));
struct data_format *tx = (struct data_format *) txbuf;
for (size_t i=0; i<32; i++) { /* digit */
for (size_t j=0; j<8; j++) { /* segment */
for (size_t k=0; k<8; k++) { /* bit */
tx[i].high[j] |= (fb->frame[k+2].data[j] & (1<<i)) ? (1<<k) : 0;
}
}
}
for (size_t i=0; i<32; i++) { /* digit */
for (size_t j=0; j<8; j++) { /* segment */
for (size_t k=0; k<2; k++) { /* bit */
tx[i].low |= (fb->frame[k].data[j] & (1<<i)) ? (1<<k<<(j*2)) : 0;
}
}
}
}
|
