feat: add src/telemetry.c

src/telemetry.c

@@ -0,0 +1,36 @@
+#include "telemetry.h"
+
+static uint8_t crc8(const uint8_t *data, size_t length) {
+    uint8_t crc = 0;
+    for (size_t i = 0; i < length; ++i) {
+        crc ^= data[i];
+        for (int bit = 0; bit < 8; ++bit)
+            crc = (uint8_t)((crc & 0x80u) ? (((unsigned)crc << 1) ^ 0x07u) : ((unsigned)crc << 1));
+    }
+    return crc;
+}
+
+frame_result_t decode_frame(const uint8_t *bytes, size_t length, sample_t *sample) {
+    if (!bytes || !sample || length != 8) return FRAME_SHORT;
+    if (bytes[0] != 1) return FRAME_VERSION;
+    if (crc8(bytes, 7) != bytes[7]) return FRAME_CRC;
+    sample->sequence = (uint16_t)((bytes[1] << 8) | bytes[2]);
+    sample->temperature_centi = (int16_t)((bytes[3] << 8) | bytes[4]);
+    sample->voltage_mv = (uint16_t)((bytes[5] << 8) | bytes[6]);
+    if (sample->temperature_centi < -4000 || sample->temperature_centi > 8500 ||
+        sample->voltage_mv < 9000 || sample->voltage_mv > 16000) return FRAME_RANGE;
+    return FRAME_OK;
+}
+
+const char *frame_result_name(frame_result_t result) {
+    switch (result) {
+        case FRAME_OK: return "accepted";
+        case FRAME_SHORT: return "invalid length";
+        case FRAME_VERSION: return "unsupported version";
+        case FRAME_CRC: return "crc mismatch";
+        case FRAME_RANGE: return "sample out of range";
+        case FRAME_DUPLICATE: return "duplicate sequence";
+        case FRAME_ROLLBACK: return "sequence rollback";
+    }
+    return "unknown";
+}