1 | /************************************************************************/
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2 | /* */
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3 | /* Software UART using T1 */
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4 | /* */
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5 | /* Author: P. Dannegger */
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6 | /* danni@specs.de */
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7 | /* */
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8 | /************************************************************************/
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9 | #include <main.h>
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10 | #include <suart.h>
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11 |
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12 |
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13 | #define BIT_TIME (u16)((XTAL + BAUD/2) / BAUD)
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14 |
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15 |
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16 | volatile u8 stx_count;
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17 | u8 stx_data;
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18 |
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19 | volatile u8 srx_done;
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20 | u8 srx_data;
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21 | u8 srx_mask;
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22 | u8 srx_tmp;
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23 |
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24 |
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25 | void suart_init( void )
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26 | {
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27 | OCR1A = TCNT1 + 1; // force first compare
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28 | TCCR1A = 1<<COM1A1^1<<COM1A0; // set OC1A high, T1 mode 0
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29 | TCCR1B = 1<<ICNC1^1<<CS10; // noise canceler, 1>0 transition,
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30 | // CLK/1, T1 mode 0
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31 | TIFR = 1<<ICF1; // clear pending interrupt
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32 | TIMSK = 1<<TICIE1^1<<OCIE1A; // enable tx and wait for start
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33 |
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34 | stx_count = 0; // nothing to sent
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35 | srx_done = 0; // nothing received
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36 | STXDDR |= 1<<STX; // TX output
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37 | }
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38 |
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39 |
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40 | u8 sgetchar( void ) // get byte
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41 | {
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42 | while( !srx_done ); // wait until byte received
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43 | srx_done = 0;
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44 | return srx_data;
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45 | }
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46 |
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47 |
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48 | SIGNAL( SIG_INPUT_CAPTURE1 ) // rx start
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49 | {
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50 | OCR1B = ICR1 + (u16)(BIT_TIME * 1.5); // scan 1.5 bits after start
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51 | srx_tmp = 0; // clear bit storage
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52 | srx_mask = 1; // bit mask
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53 | TIFR = 1<<OCF1B; // clear pending interrupt
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54 | if( !(SRXPIN & 1<<SRX)) // still low
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55 | TIMSK = 1<<OCIE1A^1<<OCIE1B; // wait for first bit
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56 | }
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57 |
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58 |
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59 | SIGNAL( SIG_OUTPUT_COMPARE1B )
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60 | {
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61 | u8 in = SRXPIN; // scan rx line
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62 |
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63 | if( srx_mask ){
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64 | if( in & 1<<SRX )
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65 | srx_tmp |= srx_mask;
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66 | srx_mask <<= 1;
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67 | OCR1B += BIT_TIME; // next bit slice
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68 | }else{
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69 | srx_done = 1; // mark rx data valid
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70 | srx_data = srx_tmp; // store rx data
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71 | TIFR = 1<<ICF1; // clear pending interrupt
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72 | TIMSK = 1<<TICIE1^1<<OCIE1A; // enable tx and wait for start
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73 | }
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74 | }
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75 |
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76 |
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77 | void sputchar( u8 val ) // send byte
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78 | {
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79 | while( stx_count ); // until last byte finished
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80 | stx_data = ~val; // invert data for Stop bit generation
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81 | stx_count = 10; // 10 bits: Start + data + Stop
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82 | }
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83 |
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84 |
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85 | void sputs( u8 *txt ) // send string
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86 | {
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87 | while( *txt )
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88 | sputchar( *txt++ );
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89 | }
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90 |
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91 |
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92 | SIGNAL( SIG_OUTPUT_COMPARE1A ) // tx bit
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93 | {
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94 | u8 dout;
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95 | u8 count;
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96 |
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97 | OCR1A += BIT_TIME; // next bit slice
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98 | count = stx_count;
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99 |
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100 | if( count ){
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101 | stx_count = --count; // count down
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102 | dout = 1<<COM1A1; // set low on next compare
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103 | if( count != 9 ){ // no start bit
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104 | if( !(stx_data & 1) ) // test inverted data
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105 | dout = 1<<COM1A1^1<<COM1A0; // set high on next compare
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106 | stx_data >>= 1; // shift zero in from left
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107 | }
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108 | TCCR1A = dout;
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109 | }
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110 | }
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