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diff --git a/protocol/ps2_busywait.c b/protocol/ps2_busywait.c
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+/*
+Copyright 2010,2011,2012,2013 Jun WAKO <wakojun@gmail.com>
+
+This software is licensed with a Modified BSD License.
+All of this is supposed to be Free Software, Open Source, DFSG-free,
+GPL-compatible, and OK to use in both free and proprietary applications.
+Additions and corrections to this file are welcome.
+
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+* Redistributions of source code must retain the above copyright
+ notice, this list of conditions and the following disclaimer.
+
+* Redistributions in binary form must reproduce the above copyright
+ notice, this list of conditions and the following disclaimer in
+ the documentation and/or other materials provided with the
+ distribution.
+
+* Neither the name of the copyright holders nor the names of
+ contributors may be used to endorse or promote products derived
+ from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.
+*/
+
+/*
+ * PS/2 protocol busywait version
+ */
+
+#include <stdbool.h>
+#include <util/delay.h>
+#include "ps2.h"
+#include "debug.h"
+
+
+#define WAIT(stat, us, err) do { \
+ if (!wait_##stat(us)) { \
+ ps2_error = err; \
+ goto ERROR; \
+ } \
+} while (0)
+
+
+uint8_t ps2_error = PS2_ERR_NONE;
+
+
+void ps2_host_init(void)
+{
+ // POR(150-2000ms) plus BAT(300-500ms) may take 2.5sec([3]p.20)
+ _delay_ms(2500);
+
+ inhibit();
+}
+
+uint8_t ps2_host_send(uint8_t data)
+{
+ bool parity = true;
+ ps2_error = PS2_ERR_NONE;
+
+ /* terminate a transmission if we have */
+ inhibit();
+ _delay_us(100); // 100us [4]p.13, [5]p.50
+
+ /* 'Request to Send' and Start bit */
+ data_lo();
+ clock_hi();
+ WAIT(clock_lo, 10000, 10); // 10ms [5]p.50
+
+ /* Data bit */
+ for (uint8_t i = 0; i < 8; i++) {
+ _delay_us(15);
+ if (data&(1<<i)) {
+ parity = !parity;
+ data_hi();
+ } else {
+ data_lo();
+ }
+ WAIT(clock_hi, 50, 2);
+ WAIT(clock_lo, 50, 3);
+ }
+
+ /* Parity bit */
+ _delay_us(15);
+ if (parity) { data_hi(); } else { data_lo(); }
+ WAIT(clock_hi, 50, 4);
+ WAIT(clock_lo, 50, 5);
+
+ /* Stop bit */
+ _delay_us(15);
+ data_hi();
+
+ /* Ack */
+ WAIT(data_lo, 50, 6);
+ WAIT(clock_lo, 50, 7);
+
+ /* wait for idle state */
+ WAIT(clock_hi, 50, 8);
+ WAIT(data_hi, 50, 9);
+
+ inhibit();
+ return ps2_host_recv_response();
+ERROR:
+ inhibit();
+ return 0;
+}
+
+/* receive data when host want else inhibit communication */
+uint8_t ps2_host_recv_response(void)
+{
+ // Command may take 25ms/20ms at most([5]p.46, [3]p.21)
+ // 250 * 100us(wait for start bit in ps2_host_recv)
+ uint8_t data = 0;
+ uint8_t try = 250;
+ do {
+ data = ps2_host_recv();
+ } while (try-- && ps2_error);
+ return data;
+}
+
+/* called after start bit comes */
+uint8_t ps2_host_recv(void)
+{
+ uint8_t data = 0;
+ bool parity = true;
+ ps2_error = PS2_ERR_NONE;
+
+ /* release lines(idle state) */
+ idle();
+
+ /* start bit [1] */
+ WAIT(clock_lo, 100, 1); // TODO: this is enough?
+ WAIT(data_lo, 1, 2);
+ WAIT(clock_hi, 50, 3);
+
+ /* data [2-9] */
+ for (uint8_t i = 0; i < 8; i++) {
+ WAIT(clock_lo, 50, 4);
+ if (data_in()) {
+ parity = !parity;
+ data |= (1<<i);
+ }
+ WAIT(clock_hi, 50, 5);
+ }
+
+ /* parity [10] */
+ WAIT(clock_lo, 50, 6);
+ if (data_in() != parity) {
+ ps2_error = PS2_ERR_PARITY;
+ goto ERROR;
+ }
+ WAIT(clock_hi, 50, 7);
+
+ /* stop bit [11] */
+ WAIT(clock_lo, 50, 8);
+ WAIT(data_hi, 1, 9);
+ WAIT(clock_hi, 50, 10);
+
+ inhibit();
+ return data;
+ERROR:
+ if (ps2_error > PS2_ERR_STARTBIT3) {
+ xprintf("x%02X\n", ps2_error);
+ }
+ inhibit();
+ return 0;
+}
+
+/* send LED state to keyboard */
+void ps2_host_set_led(uint8_t led)
+{
+ ps2_host_send(0xED);
+ ps2_host_send(led);
+}