From 9ed512b6863311ff53f07b76f6b679fa1ec6a9c9 Mon Sep 17 00:00:00 2001
From: Akshay Nair <phenax5@gmail.com>
Date: Sun, 12 Apr 2026 18:32:41 +0530
Subject: Add thermocouple sensor SPI interface

---
 compile_flags.txt |  1 +
 justfile          |  6 +++---
 src/main.c        |  8 +++++---
 src/temperature.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 src/temperature.h | 11 +++++++++++
 5 files changed, 69 insertions(+), 6 deletions(-)
 create mode 100644 src/temperature.c
 create mode 100644 src/temperature.h

diff --git a/compile_flags.txt b/compile_flags.txt
index 8d56fa5..8720d77 100644
--- a/compile_flags.txt
+++ b/compile_flags.txt
@@ -3,6 +3,7 @@
 -std=gnu99
 -Isrc
 -mmcu=attiny84a
+-DF_CPU=1000000L
 -I/nix/store/ivhsczriimr31rrmly0bcj03gv4qa3q7-avr-libc-avr-2.2.1/avr/include
 -L/nix/store/ivhsczriimr31rrmly0bcj03gv4qa3q7-avr-libc-avr-2.2.1/avr/lib
 -funsigned-char
diff --git a/justfile b/justfile
index 567f3c6..f16fda3 100644
--- a/justfile
+++ b/justfile
@@ -5,16 +5,16 @@ default:
   echo -
 
 AVR_LIBC := env("AVR_LIBC", "/usr/lib/avr")
-# F_CPU := "32768"
+F_CPU := "1000000"
 MCU := "attiny84a"
 MCU_PART := "attiny84"
-SRCS := "src/main.c src/display.c"
+SRCS := "src/main.c src/display.c src/temperature.c"
 OUTDIR := "./out"
 PROGRAMMER := "arduino"
 UPLOAD_SPEED := "19200"
 SERIAL_PORT := "/dev/ttyUSB0"
 
-CFLAGS := f"-g -Os -std=gnu99 -Isrc -mmcu={{MCU}} \
+CFLAGS := f"-g -Os -std=gnu99 -Isrc -mmcu={{MCU}} -DF_CPU={{F_CPU}}L \
 -I{{AVR_LIBC}}/avr/include -L{{AVR_LIBC}}/avr/lib \
 -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums -Wall"
 
diff --git a/src/main.c b/src/main.c
index 1b804b7..513d8b3 100644
--- a/src/main.c
+++ b/src/main.c
@@ -3,14 +3,16 @@
 #include <util/delay.h>
 
 #include "display.h"
+#include "temperature.h"
 
 int main(void) {
   display_init();
-  int n = 1;
+  temperature_init();
+  float temperature = 0;
 
   while (1) {
-    display_draw_float2(1.01 * n);
-    n = (n + 1) % 100;
+    temperature = temperature_read();
+    display_draw_float2(temperature);
     _delay_ms(1000);
   }
 
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;
+}
diff --git a/src/temperature.h b/src/temperature.h
new file mode 100644
index 0000000..31fa92a
--- /dev/null
+++ b/src/temperature.h
@@ -0,0 +1,11 @@
+#define THERMO_MISO PA0
+#define THERMO_SCK PA1
+#define THERMO_CS PA2
+#define THERMO_PORT PORTA
+#define THERMO_DDR DDRA
+
+#define SPI_DELAY_US 10
+
+void temperature_init(void);
+
+float temperature_read(void);
-- 
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