avr: Add support for sending I2C messages

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

1 files changed, 103 insertions, 0 deletions

diff --git a/src/avr/i2c.c b/src/avr/i2c.c
new file mode 100644
index 00000000..b4c0ad75
--- /dev/null
+++ b/src/avr/i2c.c
@@ -0,0 +1,103 @@
+// I2C functions on AVR
+//
+// Copyright (C) 2018  Kevin O'Connor <kevin@koconnor.net>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+
+#include <avr/io.h> // TWCR
+#include "autoconf.h" // CONFIG_CLOCK_FREQ
+#include "board/misc.h" // timer_is_before
+#include "command.h" // shutdown
+#include "gpio.h" // i2c_setup
+#include "internal.h" // GPIO
+#include "sched.h" // sched_shutdown
+
+#if CONFIG_MACH_atmega168 || CONFIG_MACH_atmega328 || CONFIG_MACH_atmega328p
+static const uint8_t SCL = GPIO('C', 5), SDA = GPIO('C', 4);
+#elif CONFIG_MACH_atmega644p || CONFIG_MACH_atmega1284p
+static const uint8_t SCL = GPIO('C', 0), SDA = GPIO('C', 1);
+#elif CONFIG_MACH_at90usb1286 || CONFIG_MACH_at90usb646 || CONFIG_MACH_atmega32u4 || CONFIG_MACH_atmega1280 || CONFIG_MACH_atmega2560
+static const uint8_t SCL = GPIO('D', 0), SDA = GPIO('D', 1);
+#endif
+
+static void
+i2c_init(void)
+{
+    if (TWCR & (1<<TWEN))
+        // Already setup
+        return;
+
+    // Setup output pins and enable pullups
+    gpio_out_setup(SDA, 1);
+    gpio_out_setup(SCL, 1);
+
+    // Set 100Khz frequency
+    TWSR = 0;
+    TWBR = ((CONFIG_CLOCK_FREQ / 100000) - 16) / 2;
+
+    // Enable interface
+    TWCR = (1<<TWEN);
+}
+
+struct i2c_config
+i2c_setup(uint32_t bus, uint32_t rate, uint8_t addr)
+{
+    if (bus)
+        shutdown("Unsupported i2c bus");
+    i2c_init();
+    return (struct i2c_config){ .addr=addr };
+}
+
+static void
+i2c_wait(uint32_t timeout)
+{
+    for (;;) {
+        if (TWCR & (1<<TWINT))
+            break;
+        if (!timer_is_before(timer_read_time(), timeout))
+            shutdown("i2c timeout");
+    }
+}
+
+static void
+i2c_start(uint32_t timeout)
+{
+    TWCR = (1<<TWEN) | (1<<TWINT) | (1<<TWSTA);
+    i2c_wait(timeout);
+    uint32_t status = TWSR;
+    if (status != 0x10 && status != 0x08)
+        shutdown("Failed to send i2c start");
+}
+
+static void
+i2c_send_byte(uint8_t b, uint32_t timeout)
+{
+    TWDR = b;
+    TWCR = (1<<TWEN) | (1<<TWINT);
+    i2c_wait(timeout);
+}
+
+static void
+i2c_stop(uint32_t timeout)
+{
+    TWCR = (1<<TWEN) | (1<<TWINT) | (1<<TWSTO);
+}
+
+void
+i2c_write(struct i2c_config config, uint8_t write_len, uint8_t *write)
+{
+    uint32_t timeout = timer_read_time() + timer_from_us(5000);
+
+    i2c_start(timeout);
+    i2c_send_byte(config.addr, timeout);
+    while (write_len--)
+        i2c_send_byte(*write++, timeout);
+    i2c_stop(timeout);
+}
+
+void
+i2c_read(struct i2c_config config, uint8_t reg_len, uint8_t *reg
+         , uint8_t read_len, uint8_t *read)
+{
+    shutdown("i2c_read not supported on avr");
+}