Add initial 1-Wire support and use it for the USB serial #

[temper-clone.git] / w1.c

diff --git a/w1.c b/w1.c
new file mode 100644 (file)
index 0000000..8217602
--- /dev/null
+++ b/w1.c
@@ -0,0 +1,126 @@
+/*
+ * Basic routines to bit-bang standard 1-Wire via a GPIO pin
+ *
+ * Copyright 2018 Jonathan McDowell <noodles@earth.li>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <stdbool.h>
+#include <avr/io.h>
+#include <util/atomic.h>
+#include <util/delay.h>
+
+#include "w1.h"
+
+uint8_t w1_crc(uint8_t *buf, uint8_t len)
+{
+       uint8_t i, j, crc;
+
+       crc = 0;
+       for (i = 0; i < len; i++)
+       {
+               crc ^= buf[i];
+               for (j = 0; j < 8; j++)
+               {
+                       crc = crc >> 1 ^ ((crc & 1) ? 0x8c : 0);
+               }
+       }
+
+       return crc;
+}
+
+void w1_write(uint8_t val)
+{
+       uint8_t i;
+
+       for (i = 0; i < 8; i++) {
+               ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
+               {
+                       /* Pull low for 6µs for 1, 60µs for 0 */
+                       DDRB |= 1 << W1_PIN;
+                       if (val & 1)
+                               _delay_us(6);
+                       else
+                               _delay_us(60);
+                       /* Release to make up to 70µs total */
+                       DDRB &= ~(1 << W1_PIN);
+                       if (val & 1)
+                               _delay_us(64);
+                       else
+                               _delay_us(10);
+               }
+
+               val >>= 1;
+       }
+}
+
+uint8_t w1_read_byte()
+{
+       uint8_t i, val;
+
+       val = 0;
+       for (i = 0; i < 8; i++) {
+               ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
+               {
+                       /* Pull low for 6µs */
+                       DDRB |= 1 << W1_PIN;
+                       _delay_us(6);
+                       /* Release for 9µs */
+                       DDRB &= ~(1 << W1_PIN);
+                       _delay_us(9);
+
+                       /* Read the line state */
+                       val |= ((PINB >> W1_PIN) & 1) << i;
+               }
+
+               _delay_us(55);
+       }
+
+       return val;
+}
+
+void w1_read(uint8_t *buf, uint8_t len)
+{
+       uint8_t i;
+
+       for (i = 0; i < len; i++) {
+               buf[i] = w1_read_byte();
+       }
+}
+
+bool w1_reset(void)
+{
+       bool present;
+
+       /* Pull low for 480µs */
+       DDRB |= 1 << W1_PIN;
+       _delay_us(480);
+       /* Release for 70µs */
+       DDRB &= ~(1 << W1_PIN);
+       _delay_us(70);
+
+       /* If there's a device present it'll have pulled the line low */
+       present = !((PINB >> W1_PIN) & 1);
+
+       /* Wait for reset to complete */
+       _delay_us(410);
+
+       return present;
+}
+
+void w1_setup(void)
+{
+       /* Set 1w pin to low */
+       PORTB &= (1 << W1_PIN);
+}