Add thermocouple sensor SPI interface

1 files changed, 49 insertions, 0 deletions

diff --git a/src/temperature.c b/src/temperature.c
new file mode 100644
index 0000000..b804fc9
--- /dev/null
+++ b/src/temperature.c
@@ -0,0 +1,49 @@
+#include <avr/io.h>
+#include <util/delay.h>
+
+#include "temperature.h"
+
+void temperature_init(void) {
+  THERMO_DDR |= (1 << THERMO_CS) | (1 << THERMO_SCK);
+  THERMO_DDR &= ~(1 << THERMO_MISO);
+  THERMO_PORT |= (1 << THERMO_CS);
+}
+
+uint8_t spi_read8(void) {
+  int i;
+  uint8_t data = 0;
+
+  for (i = 7; i >= 0; i--) {
+    THERMO_PORT &= ~(1 << THERMO_SCK);
+    _delay_us(SPI_DELAY_US);
+    if (PINA & (1 << THERMO_MISO))
+      data |= (1 << i);
+
+    THERMO_PORT |= (1 << THERMO_SCK);
+    _delay_us(SPI_DELAY_US);
+  }
+
+  return data;
+}
+
+uint16_t spi_read16(void) {
+  uint16_t data;
+  _delay_us(SPI_DELAY_US);
+  data = spi_read8();
+  data <<= 8;
+  data |= spi_read8();
+  return data;
+}
+
+float temperature_read(void) {
+  THERMO_PORT &= ~(1 << THERMO_CS);
+  uint16_t v = spi_read16();
+  THERMO_PORT |= (1 << THERMO_CS);
+
+  // invalid temp
+  if (v & 0x4)
+    return 999.9;
+
+  v >>= 3;
+  return v * 0.25;
+}