altos: Add bit-bang i2c driver

Useful for debugging stuff, not useful for flight code as it
burns the CPU for timing.

Signed-off-by: Keith Packard <keithp@keithp.com>

diff --git a/src/kernel/ao_i2c_bit.c b/src/kernel/ao_i2c_bit.c
new file mode 100644 (file)
index 0000000..01d677b
--- /dev/null
+++ b/src/kernel/ao_i2c_bit.c
@@ -0,0 +1,201 @@
+/*
+ * Copyright © 2021 Keith Packard <keithp@keithp.com>
+ *
+ * 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 2 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, write to the Free Software Foundation, Inc.,
+ * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
+ */
+
+#include <ao_i2c_bit.h>
+#include <ao_exti.h>
+
+#define ao_i2c_bit_set_pin(port, pin) do {                             \
+               ao_enable_output(port, pin, 1);                         \
+               ao_gpio_set_output_mode(port, pin, AO_OUTPUT_OPEN_DRAIN); \
+               ao_gpio_set_mode(port, pin, AO_EXTI_MODE_PULL_UP);      \
+               stm_ospeedr_set(port, pin, STM_OSPEEDR_10MHz);          \
+       } while(0)
+
+
+/* 2µS per half-cycle, for a 125kHz i2c clock */
+#define AO_I2C_TICK    10000
+
+static void
+tick(void)
+{
+       int i;
+
+       for (i = 0; i < 12; i++)
+               ao_arch_nop();
+#if 0
+       uint64_t        target = ao_time_ns() + AO_I2C_TICK;
+
+       do {
+               ao_yield();
+       } while ((int64_t) (ao_time_ns() - target) < 0);
+#endif
+}
+
+static void sda(uint8_t v)
+{
+       ao_gpio_set(AO_I2C_SDA_PORT, AO_I2C_SDA_PIN, v);
+       tick();
+}
+
+static uint8_t in(void)
+{
+       uint8_t v = ao_gpio_get(AO_I2C_SDA_PORT, AO_I2C_SDA_PIN);
+       tick();
+       return v;
+}
+
+static void scl(uint8_t v)
+{
+       ao_gpio_set(AO_I2C_SCL_PORT, AO_I2C_SCL_PIN, v);
+       tick();
+}
+
+static void
+i2c_start(void)
+{
+       sda(0);
+       scl(0);
+}
+
+static bool
+ack(void)
+{
+       bool v;
+       int j;
+
+       sda(1);
+       scl(1);
+       v = false;
+       for (j = 0; j < 100; j++) {
+               if (in() == 0) {
+                       v = true;
+                       break;
+               }
+       }
+       scl(0);
+       sda(1);
+       ao_yield();
+       return v;
+}
+
+static bool
+send(uint8_t byte)
+{
+       uint8_t bit;
+
+       for (bit = 0; bit < 8; bit++) {
+               sda(byte>>7);
+               scl(1);
+               tick();
+               scl(0);
+               byte <<= 1;
+       }
+       return ack();
+}
+
+static uint8_t
+recv(void)
+{
+       uint8_t byte = 0;
+       uint8_t bit;
+
+       for (bit = 0; bit < 8; bit++) {
+               sda(1);
+               scl(1);
+               byte = (byte << 1) | in();
+               scl(0);
+       }
+       ack();
+       return byte;
+}
+
+static void
+stop(void)
+{
+       sda(0);
+       scl(1);
+       sda(1);
+}
+
+static void
+restart(void)
+{
+       sda(1);
+       scl(1);
+       sda(0);
+       scl(0);
+}
+
+static uint8_t
+ao_i2c_bit_mutex;
+
+void
+ao_i2c_bit_get(void)
+{
+       ao_mutex_get(&ao_i2c_bit_mutex);
+}
+
+void
+ao_i2c_bit_put(void)
+{
+       ao_mutex_put(&ao_i2c_bit_mutex);
+}
+
+bool
+ao_i2c_bit_start(uint8_t addr)
+{
+       i2c_start();
+       return send(addr);
+}
+
+bool
+ao_i2c_bit_restart(uint8_t addr)
+{
+       restart();
+       return send(addr);
+}
+
+void
+ao_i2c_bit_stop(void)
+{
+       stop();
+}
+
+void
+ao_i2c_bit_send(void *block, uint16_t len)
+{
+       uint8_t *b = block;
+       while (len--)
+               send(*b++);
+}
+
+void
+ao_i2c_bit_recv(void *block, uint16_t len)
+{
+       uint8_t *b = block;
+
+       while (len--)
+               *b++ = recv();
+}
+
+void
+ao_i2c_bit_init(void)
+{
+       ao_i2c_bit_set_pin(AO_I2C_SCL_PORT, AO_I2C_SCL_PIN);
+       ao_i2c_bit_set_pin(AO_I2C_SDA_PORT, AO_I2C_SDA_PIN);
+}

diff --git a/src/kernel/ao_i2c_bit.h b/src/kernel/ao_i2c_bit.h
new file mode 100644 (file)
index 0000000..bb9807f
--- /dev/null
+++ b/src/kernel/ao_i2c_bit.h
@@ -0,0 +1,43 @@
+/*
+ * Copyright © 2021 Keith Packard <keithp@keithp.com>
+ *
+ * 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 2 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, write to the Free Software Foundation, Inc.,
+ * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
+ */
+
+#include <ao.h>
+
+void
+ao_i2c_bit_get(void);
+
+void
+ao_i2c_bit_put(void);
+
+bool
+ao_i2c_bit_start(uint8_t addr);
+
+bool
+ao_i2c_bit_restart(uint8_t addr);
+
+void
+ao_i2c_bit_stop(void);
+
+void
+ao_i2c_bit_send(void *block, uint16_t len);
+
+void
+ao_i2c_bit_recv(void *block, uint16_t len);
+
+void
+ao_i2c_bit_init(void);