Root/tornado/fw/led.c

1/*
2 * fw/led.c - LED control
3 *
4 * Written 2012 by Werner Almesberger
5 * Copyright 2012 Werner Almesberger
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation; either version 2 of the License, or
10 * (at your option) any later version.
11 */
12
13
14#include <stdint.h>
15
16#include <avr/io.h>
17#include <avr/interrupt.h>
18#include <avr/pgmspace.h>
19#define F_CPU 8000000UL
20#include <util/delay.h>
21
22#include "io.h"
23#include "led.h"
24
25
26void led_show(const uint8_t p[LED_BYTES])
27{
28    uint8_t i;
29
30    for (i = 0; i != LED_BYTES; i++) {
31        while (!(UCSR0A & (1 << UDRE0)));
32        UDR0 = p[i];
33    }
34
35    /*
36     * There doesn't seem to be any reliable way to synchronize with the
37     * end of the shift operation register that wouldn't cli/sei. Note
38     * that, since the receiver is disabled, we can't use the RX side for
39     * this purpose (as it is done in the atusb firmware).
40     *
41     * So instead we just wait for the worst-case delay, being one byte
42     * in the shift register and another byte in the transmit buffer,
43     * giving a total of 16 bits.
44     *
45     * This is a bit too pessimistic and produces a slight extra delay of
46     * about 1.8 us. (The whole pattern transmission takes 16 us.)
47     * See also ../doc/lclk-1123.png
48     */
49
50    _delay_us(4); /* 16 bits at 4 MHz */
51    SET(LED_LCLK);
52    CLR(LED_LCLK);
53}
54
55
56void led_show_pgm(const prog_uint8_t p[LED_BYTES])
57{
58    uint8_t i;
59
60    for (i = 0; i != LED_BYTES; i++) {
61        while (!(UCSR0A & (1 << UDRE0)));
62        UDR0 = pgm_read_byte(p+i);
63    }
64
65    _delay_us(4); /* 16 bits at 4 MHz */
66    SET(LED_LCLK);
67    CLR(LED_LCLK);
68}
69
70
71void led_off(void)
72{
73    static uint8_t zero[LED_BYTES] PROGMEM = { 0, };
74
75    led_show_pgm(zero);
76}
77
78
79void led_init(void)
80{
81    CLR(LED_SCLK);
82    OUT(LED_SCLK);
83    CLR(LED_LCLK);
84    OUT(LED_LCLK);
85
86    UBRR0 = 0; /* maximum data rate */
87    UCSR0C =
88        1 << UMSEL01 | /* Master SPI */
89        1 << UMSEL00 |
90        1 << UDORD0 | /* MSB first */
91        0 << UCPHA0 | /* SPI Mode 0 */
92        0 << UCPOL0;
93    UCSR0B =
94        1 << TXEN0; /* enable transmitter */
95    UBRR0 = 0; /* the manual sez we need this */
96
97    led_off();
98}
99

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