From be5b5ca2d522731df2133d646881c7635a232d50 Mon Sep 17 00:00:00 2001
From: Travis Shears <t@travisshears.com>
Date: Wed, 9 Apr 2025 12:07:18 +0200
Subject: [PATCH] convert bme280 pressure number

---
 bme280.c | 56 +++++++++++++++++++++++++++++++++++++++++++++-----------
 bme280.h |  2 +-
 node1.c  |  2 +-
 3 files changed, 47 insertions(+), 13 deletions(-)

diff --git a/bme280.c b/bme280.c
index 74bd2dd..9bf5904 100644
--- a/bme280.c
+++ b/bme280.c
@@ -115,9 +115,9 @@ static void bmp280_get_compensation_params(i2c_inst_t *i2c,
   params->dig_h5 = (int16_t)(buf[33] << 8) | buf[32];
 }
 
-// Main Config for the sensor. Defined here so it can be use to inital configure the sensor and to proc further reads
-// 001 sets osrs_t temp over sampling to 1, 001 sets osrs_p pressure
-// oversampling to 1, 01 sets sensor mode to forced
+// Main Config for the sensor. Defined here so it can be use to inital configure
+// the sensor and to proc further reads 001 sets osrs_t temp over sampling to 1,
+// 001 sets osrs_p pressure oversampling to 1, 01 sets sensor mode to forced
 static const uint8_t main_config = 0b00100101;
 void bme280_init(bme280_config *config, i2c_inst_t *i2c, uint8_t sda_pin,
                  uint8_t scl_pin) {
@@ -179,7 +179,7 @@ static void bme280_read_raw(bme280_config *config, int32_t *temp,
   *temp = (buf[3] << 12) | (buf[4] << 4) | (buf[5] >> 4);
 }
 
-float bmp280_convert_temp(bme280_config *config, int32_t temp) {
+static int32_t bme280_caculate_t_fine(bme280_config *config, int32_t temp) {
   bme280_compensation_params params = config->params;
   int32_t var1, var2;
   var1 = ((((temp >> 3) - ((int32_t)params.dig_t1 << 1))) *
@@ -190,11 +190,44 @@ float bmp280_convert_temp(bme280_config *config, int32_t temp) {
            12) *
           ((int32_t)params.dig_t3)) >>
          14;
-  int32_t var3 = var1 + var2;
-  // uses the BMP280 calibration parameters to compensate the temperature value
-  // read from its registers
-  int32_t var4 = (var3 * 5 + 128) >> 8;
-  return (float)var4 / 100;
+  return var1 + var2;
+}
+
+float bme280_convert_temp(int32_t t_fine) {
+  int32_t temp = (t_fine * 5 + 128) >> 8;
+  return (float)temp / 100;
+}
+
+float bmp280_convert_pressure(bme280_config *config, int32_t t_fine,
+                              int32_t pressure) {
+  bme280_compensation_params params = config->params;
+  int32_t var1, var2;
+  uint32_t converted = 0.0;
+  var1 = (((int32_t)t_fine) >> 1) - (int32_t)64000;
+  var2 = (((var1 >> 2) * (var1 >> 2)) >> 11) * ((int32_t)params.dig_p6);
+  var2 += ((var1 * ((int32_t)params.dig_p5)) << 1);
+  var2 = (var2 >> 2) + (((int32_t)params.dig_p4) << 16);
+  var1 = (((params.dig_p3 * (((var1 >> 2) * (var1 >> 2)) >> 13)) >> 3) +
+          ((((int32_t)params.dig_p2) * var1) >> 1)) >>
+         18;
+  var1 = ((((32768 + var1)) * ((int32_t)params.dig_p1)) >> 15);
+  if (var1 == 0) {
+    return 0; // avoid exception caused by division by zero
+  }
+  converted =
+      (((uint32_t)(((int32_t)1048576) - pressure) - (var2 >> 12))) * 3125;
+  if (converted < 0x80000000) {
+    converted = (converted << 1) / ((uint32_t)var1);
+  } else {
+    converted = (converted / (uint32_t)var1) * 2;
+  }
+  var1 = (((int32_t)params.dig_p9) *
+          ((int32_t)(((converted >> 3) * (converted >> 3)) >> 13))) >>
+         12;
+  var2 = (((int32_t)(converted >> 2)) * ((int32_t)params.dig_p8)) >> 13;
+  converted =
+      (uint32_t)((int32_t)converted + ((var1 + var2 + params.dig_p7) >> 4));
+  return (float)converted / 100;
 }
 
 bme280_reading bme280_read(bme280_config *config) {
@@ -206,8 +239,9 @@ bme280_reading bme280_read(bme280_config *config) {
   int32_t raw_humidity = 0;
   bme280_read_raw(config, &raw_temperature, &raw_pressure, &raw_humidity);
   bme280_reading reading;
-  reading.temperature = bmp280_convert_temp(config, raw_temperature);
-  reading.pressure = raw_pressure;
+  int32_t t_fine = bme280_caculate_t_fine(config, raw_temperature);
+  reading.temperature = bme280_convert_temp(t_fine);
+  reading.pressure = bmp280_convert_pressure(config, t_fine, raw_pressure);
   reading.humidity = raw_humidity;
   return reading;
 }
diff --git a/bme280.h b/bme280.h
index 4eef6a7..d136be6 100644
--- a/bme280.h
+++ b/bme280.h
@@ -33,7 +33,7 @@ typedef struct {
 
 typedef struct {
   float temperature;
-  int32_t pressure;
+  float pressure;
   int32_t humidity;
 } bme280_reading;
 
diff --git a/node1.c b/node1.c
index 474cf8f..c71e210 100644
--- a/node1.c
+++ b/node1.c
@@ -15,7 +15,7 @@ int main() {
         printf("Making reading\n");
         current_reading = bme280_read(&config);
         printf("Tempature: %.2f\n", current_reading.temperature);
-        printf("Pressure: %d\n", current_reading.pressure);
+        printf("Pressure: %.2f\n", current_reading.pressure);
         printf("Humidity: %d\n", current_reading.humidity);
     }
 }