Improve ina260 example (#771)

Set the config register.
Fix issue with overflow.

Author: peterharperuk

i2c/ina260_i2c/ina260_i2c.c

@@ -10,12 +10,53 @@
 #define POWER_REGISTER 0x03
 #define I2C_ADDRESS 0x40
 
-#define ByteSwap(u)  (uint16_t)((u << 8)|(u >> 8))
+#define CONFIG_REGISTER 0x00
 
 #ifndef RTC_CLOCK_SRC_GPIO_OUT
 #define RTC_CLOCK_SRC_GPIO_OUT 21
 #endif
 
+// Averaging: number of samples the INA260 averages in hardware before updating
+// its registers (CONFIG register AVG field, bits 11:9). More = quieter readings
+// but slower updates. Helpful for low sleep currents.
+// Allowed values: 1, 4, 16, 64, 128, 256, 512, 1024.
+#define AVG_SAMPLES 128
+
+#if   AVG_SAMPLES == 1
+  #define AVG_FIELD 0
+#elif AVG_SAMPLES == 4
+  #define AVG_FIELD 1
+#elif AVG_SAMPLES == 16
+  #define AVG_FIELD 2
+#elif AVG_SAMPLES == 64
+  #define AVG_FIELD 3
+#elif AVG_SAMPLES == 128
+  #define AVG_FIELD 4
+#elif AVG_SAMPLES == 256
+  #define AVG_FIELD 5
+#elif AVG_SAMPLES == 512
+  #define AVG_FIELD 6
+#elif AVG_SAMPLES == 1024
+  #define AVG_FIELD 7
+#else
+  #error "AVG_SAMPLES must be one of: 1, 4, 16, 64, 128, 256, 512, 1024"
+#endif
+
+// CONFIG register value:
+//   bit 15      reset (0)
+//   bits 11:9   AVG = samples averaged
+//   bits 8:6    VBUSCT, 5:3 ISHCT = conversion times (left at default 0b100 = 1.1 ms)
+//   bits 2:0    MODE = 0b111 (continuous shunt + bus)
+#define CONFIG_VALUE ( ((AVG_FIELD & 0x7) << 9) \
+                     | (0x4 << 6)  /* VBUSCT 1.1 ms */ \
+                     | (0x4 << 3)  /* ISHCT  1.1 ms */ \
+                     | 0x7 )       /* continuous shunt + bus */
+
+// Swap the byte order of a 16-bit value (INA260 returns big-endian over I2C).
+static inline uint16_t byte_swap(uint16_t u) {
+    return (uint16_t)((u << 8) | (u >> 8));
+}
+
 // Read register value
 static uint16_t read_reg(uint8_t reg) {
     // Set the register address
@@ -27,7 +68,15 @@ static uint16_t read_reg(uint8_t reg) {
     ret = i2c_read_blocking(i2c_default, I2C_ADDRESS, (uint8_t*)&data, 2, false);
     assert(ret == 2);
     if (ret != 2) return 0;
-    return ByteSwap(data);
+    return byte_swap(data);
+}
+
+// Write a 16-bit register value
+static void write_reg(uint8_t reg, uint16_t value) {
+    uint8_t buf[3] = { reg, (uint8_t)(value >> 8), (uint8_t)(value & 0xFF) };
+    int ret = i2c_write_blocking(i2c_default, I2C_ADDRESS, buf, 3, false);
+    assert(ret == 3);
+    (void)ret;
 }
 
 int main() {
@@ -53,23 +102,28 @@ int main() {
     gpio_pull_up(PICO_DEFAULT_I2C_SDA_PIN);
     gpio_pull_up(PICO_DEFAULT_I2C_SCL_PIN);
 
+    // Configure averaging + continuous mode (see CONFIG_VALUE above).
+    write_reg(CONFIG_REGISTER, CONFIG_VALUE);
+
     hard_assert(status_led_init());
     while(true) {
         status_led_set_state(true);
 
-        // Read current and convert to mA
-        float ma = read_reg(CURRENT_REGISTER) * 1.250f;
-        if (ma > 15000) ma = 0;
-        // Read the voltage
+        // Read current and convert to mA. The CURRENT register is signed
+        // (two's complement), so cast through int16_t before scaling -- otherwise
+        // small negative or near-zero readings wrap to a huge positive number.
+        float ma = (int16_t)read_reg(CURRENT_REGISTER) * 1.25f;
+        // Read the voltage (1.25 mV/LSB, unsigned)
         float v = read_reg(VOLTAGE_REGISTER) * 0.00125f;
-        // Read power and convert to mW
-        uint16_t mw = read_reg(POWER_REGISTER) * 10;
-    
+        // Read power and convert to mW (10 mW/LSB). Use 32-bit: register x 10
+        // exceeds uint16_t range.
+        uint32_t mw = (uint32_t)read_reg(POWER_REGISTER) * 10;
+
         // Display results
-        printf("current: %.2f mA voltage: %.2f V power: %u mW\n", ma, v, mw);
+        printf("current: %.2f mA voltage: %.2f V power: %lu mW\n", ma, v, (unsigned long)mw);
 
         status_led_set_state(false);
         sleep_ms(1000);
     }
     return 0;
-}
+}