xt_interrupt.c (4923B)
1 /* 2 Copyright 2018 Jun WAKO <wakojun@gmail.com> 3 Copyright 2016 Ethan Apodaca <papodaca@gmail.com> 4 5 This software is licensed with a Modified BSD License. 6 All of this is supposed to be Free Software, Open Source, DFSG-free, 7 GPL-compatible, and OK to use in both free and proprietary applications. 8 Additions and corrections to this file are welcome. 9 10 11 Redistribution and use in source and binary forms, with or without 12 modification, are permitted provided that the following conditions are met: 13 14 * Redistributions of source code must retain the above copyright 15 notice, this list of conditions and the following disclaimer. 16 17 * Redistributions in binary form must reproduce the above copyright 18 notice, this list of conditions and the following disclaimer in 19 the documentation and/or other materials provided with the 20 distribution. 21 22 * Neither the name of the copyright holders nor the names of 23 contributors may be used to endorse or promote products derived 24 from this software without specific prior written permission. 25 26 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 27 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29 ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 30 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 31 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 32 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 33 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 34 CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 35 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 36 POSSIBILITY OF SUCH DAMAGE. 37 */ 38 39 #include <stdbool.h> 40 #include <avr/interrupt.h> 41 #include "xt.h" 42 #include "wait.h" 43 #include "debug.h" 44 45 static inline uint8_t pbuf_dequeue(void); 46 static inline void pbuf_enqueue(uint8_t data); 47 static inline bool pbuf_has_data(void); 48 static inline void pbuf_clear(void); 49 50 void xt_host_init(void) { 51 XT_INT_INIT(); 52 XT_INT_OFF(); 53 54 /* hard reset */ 55 #ifdef XT_RESET 56 XT_RESET(); 57 #endif 58 59 /* soft reset: pull clock line down for 20ms */ 60 XT_DATA_LO(); 61 XT_CLOCK_LO(); 62 wait_ms(20); 63 64 /* input mode with pullup */ 65 XT_CLOCK_IN(); 66 XT_DATA_IN(); 67 68 XT_INT_ON(); 69 } 70 71 /* get data received by interrupt */ 72 uint8_t xt_host_recv(void) { 73 if (pbuf_has_data()) { 74 return pbuf_dequeue(); 75 } else { 76 return 0; 77 } 78 } 79 80 ISR(XT_INT_VECT) { 81 /* 82 * XT signal format consits of 10 or 9 clocks and sends start bits and 8-bit data, 83 * which should be read on falling edge of clock. 84 * 85 * start(0), start(1), bit0, bit1, bit2, bit3, bit4, bit5, bit6, bit7 86 * 87 * Original IBM XT keyboard sends start(0) bit while some of clones don't. 88 * Start(0) bit is read as low on data line while start(1) as high. 89 * 90 * https://github.com/tmk/tmk_keyboard/wiki/IBM-PC-XT-Keyboard-Protocol 91 */ 92 static enum { START, BIT0, BIT1, BIT2, BIT3, BIT4, BIT5, BIT6, BIT7 } state = START; 93 static uint8_t data = 0; 94 95 uint8_t dbit = XT_DATA_READ(); 96 97 // This is needed if using PCINT which can be called on both falling and rising edge 98 // if (XT_CLOCK_READ()) return; 99 100 switch (state) { 101 case START: 102 // ignore start(0) bit 103 if (!dbit) return; 104 break; 105 case BIT0 ... BIT7: 106 data >>= 1; 107 if (dbit) data |= 0x80; 108 break; 109 } 110 if (state++ == BIT7) { 111 pbuf_enqueue(data); 112 state = START; 113 data = 0; 114 } 115 return; 116 } 117 118 /*-------------------------------------------------------------------- 119 * Ring buffer to store scan codes from keyboard 120 *------------------------------------------------------------------*/ 121 #define PBUF_SIZE 32 122 static uint8_t pbuf[PBUF_SIZE]; 123 static uint8_t pbuf_head = 0; 124 static uint8_t pbuf_tail = 0; 125 126 static inline void pbuf_enqueue(uint8_t data) { 127 uint8_t sreg = SREG; 128 cli(); 129 uint8_t next = (pbuf_head + 1) % PBUF_SIZE; 130 if (next != pbuf_tail) { 131 pbuf[pbuf_head] = data; 132 pbuf_head = next; 133 } else { 134 dprintf("pbuf: full\n"); 135 } 136 SREG = sreg; 137 } 138 139 static inline uint8_t pbuf_dequeue(void) { 140 uint8_t val = 0; 141 142 uint8_t sreg = SREG; 143 cli(); 144 if (pbuf_head != pbuf_tail) { 145 val = pbuf[pbuf_tail]; 146 pbuf_tail = (pbuf_tail + 1) % PBUF_SIZE; 147 } 148 SREG = sreg; 149 150 return val; 151 } 152 153 static inline bool pbuf_has_data(void) { 154 uint8_t sreg = SREG; 155 cli(); 156 bool has_data = (pbuf_head != pbuf_tail); 157 SREG = sreg; 158 return has_data; 159 } 160 161 static inline void pbuf_clear(void) { 162 uint8_t sreg = SREG; 163 cli(); 164 pbuf_head = pbuf_tail = 0; 165 SREG = sreg; 166 }