restructured i2c-max split, added BMS unit test

src/max17048.c

@@ -118,3 +118,58 @@ void bms_checker_task(void *pvParameters) {
     }
   }
 }
+
+// Helper: Read 16-bit register to 2-byte array (MSB first big endian)
+esp_err_t max17048_read_reg(uint8_t reg_addr, uint8_t *MSB, uint8_t *LSB) {  
+  // this is better than converting to little endian for my application
+  // since I usually need to handle bytes individually.
+  uint8_t data[2];
+  // Write register address
+  i2c_cmd_handle_t cmd = i2c_cmd_link_create();
+  i2c_master_start(cmd);
+  i2c_master_write_byte(cmd, (MAX17048_ADDR << 1) | I2C_MASTER_WRITE, true);
+  i2c_master_write_byte(cmd, reg_addr, true);
+  
+  // Restart and Read 2 bytes
+  i2c_master_start(cmd);
+  i2c_master_write_byte(cmd, (MAX17048_ADDR << 1) | I2C_MASTER_READ, true);
+  i2c_master_read(cmd, data, 2, I2C_MASTER_LAST_NACK);
+  i2c_master_stop(cmd);
+  
+  esp_err_t ret = i2c_master_cmd_begin(I2C_MASTER_NUM, cmd, pdMS_TO_TICKS(I2C_MASTER_TIMEOUT_MS));
+  i2c_cmd_link_delete(cmd);
+
+  if (ret == ESP_OK) {
+    *MSB = data[0];
+    *LSB = data[1];
+  }
+
+  return ret;
+}
+
+// Write big endian 2-byte array to a 16-bit register
+esp_err_t max17048_write_reg(uint8_t reg_addr, uint8_t MSB, uint8_t LSB) {
+  // Write register address
+  i2c_cmd_handle_t cmd = i2c_cmd_link_create();
+  i2c_master_start(cmd);
+  i2c_master_write_byte(cmd, (MAX17048_ADDR << 1) | I2C_MASTER_WRITE, true);
+  i2c_master_write_byte(cmd, reg_addr, true);
+  i2c_master_write_byte(cmd, MSB, true);
+  i2c_master_write_byte(cmd, LSB, true);
+  i2c_master_stop(cmd);
+  
+  esp_err_t ret = i2c_master_cmd_begin(I2C_MASTER_NUM, cmd, pdMS_TO_TICKS(I2C_MASTER_TIMEOUT_MS));
+  i2c_cmd_link_delete(cmd);
+  return ret;
+}
+
+esp_err_t max17048_friendly_write_reg(uint8_t reg_addr, uint8_t MSB, uint8_t LSB,
+  uint8_t MSBmask, uint8_t LSBmask) {
+  uint8_t origMSB, origLSB;
+  esp_err_t err = max17048_read_reg(reg_addr, &origMSB, &origLSB);
+  MSB &= MSBmask;
+  LSB &= LSBmask;
+  MSB |= origMSB & ~MSBmask;
+  LSB |= origLSB & ~LSBmask;
+  return err | max17048_write_reg(reg_addr, MSB, LSB);
+}