SoftUART.c 3.56 KB
Newer Older
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
/*
			 LUFA Library
	 Copyright (C) Dean Camera, 2010.
			  
  dean [at] fourwalledcubicle [dot] com
	  www.fourwalledcubicle.com
*/

/*
  Copyright 2010  David Prentice (david.prentice [at] farming [dot] uk)
  Copyright 2010  Peter Danneger
  Copyright 2010  Dean Camera (dean [at] fourwalledcubicle [dot] com)

  Permission to use, copy, modify, distribute, and sell this 
  software and its documentation for any purpose is hereby granted
  without fee, provided that the above copyright notice appear in 
  all copies and that both that the copyright notice and this
  permission notice and warranty disclaimer appear in supporting 
  documentation, and that the name of the author not be used in 
  advertising or publicity pertaining to distribution of the 
  software without specific, written prior permission.

  The author disclaim all warranties with regard to this
  software, including all implied warranties of merchantability
  and fitness.  In no event shall the author be liable for any
  special, indirect or consequential damages or any damages
  whatsoever resulting from loss of use, data or profits, whether
  in an action of contract, negligence or other tortious action,
  arising out of or in connection with the use or performance of
  this software.
*/

#include "SoftUART.h"

volatile uint8_t srx_done, stx_count;
volatile uint8_t srx_data, srx_mask, srx_tmp, stx_data;

uint8_t SoftUART_IsReady(void)
{
	return !(stx_count);
}

uint8_t SoftUART_TxByte(uint8_t Byte)
{
	while (stx_count);

	stx_data  = ~Byte;
	stx_count = 10;

	return Byte;
}

uint8_t SoftUART_IsReceived(void)
{
	return srx_done;
}

uint8_t SoftUART_RxByte(void)
{
	while (!(srx_done));

	srx_done = 0;

	return srx_data;
}

void SoftUART_Init(void)
{
	OCR2B  = TCNT2 + 1;						// force first compare
	TCCR2A = (1 << COM2B1) | (1 << COM2B0);	// T1 mode 0
	TCCR2B = (1 << FOC2B)  | (1 << CS21); 	// CLK/8, T1 mode 0
	TIMSK2 = (1 << OCIE2B);					// enable tx and wait for start
	EICRA  = (1 << ISC01);					// -ve edge
	EIMSK  = (1 << INT0);					// enable INT0 interrupt

	stx_count = 0;							// nothing to send
	srx_done = 0;							// nothing received
	STXPORT |= 1 << STX;					// TX output
	STXDDR  |= 1 << STX;					// TX output
	SRXPORT |= (1 << SRX);					// pullup on INT0
}

/* ISR to detect the start of a bit being sent from the transmitter. */
ISR(INT0_vect)
{
	OCR2A = TCNT2 + (BIT_TIME / 8 * 3 / 2);	// scan 1.5 bits after start

	srx_tmp = 0;							// clear bit storage
	srx_mask = 1;							// bit mask

	TIFR2 = (1 << OCF2A);					// clear pending interrupt

	if (!(SRXPIN & (1 << SRX)))				// still low
	{
		TIMSK2 = (1 << OCIE2A) | (1 << OCIE2B); // wait for first bit
		EIMSK &= ~(1 << INT0);
	}
}

/* ISR to manage the reception of bits to the transmitter. */
ISR(TIMER2_COMPA_vect)
{
	if (srx_mask)
	{
		if (SRXPIN & (1 << SRX))
		  srx_tmp |= srx_mask;

		srx_mask <<= 1;

		OCR2A += BIT_TIME / 8;				// next bit slice
	}
	else
	{
		srx_done  = 1;						// mark rx data valid
		srx_data  = srx_tmp;				// store rx data
		TIMSK2    = (1 << OCIE2B);			// enable tx and wait for start
		EIMSK    |= (1 << INT0);			// enable START irq
		EIFR      = (1 << INTF0);			// clear any pending
	}
}

/* ISR to manage the transmission of bits to the receiver. */
ISR(TIMER2_COMPB_vect)
{
	OCR2B += BIT_TIME / 8;					// next bit slice

	if (stx_count)
	{
		if (--stx_count != 9)				// no start bit
		{
			if (!(stx_data & 1))			// test inverted data
			  TCCR2A = (1 << COM2B1) | (1 << COM2B0);
			else
			  TCCR2A = (1 << COM2B1);

			stx_data >>= 1;					// shift zero in from left
		}
		else
		{
			TCCR2A = (1 << COM2B1);			// START bit
		}
	}
}