Added battery percentage and low battery indicate

* Raised low framerate to 11hz to get better feeling input latency
* Added question of Odroid-go-firmware license and note that I do use
their code

ReadMe.org

@@ -76,4 +76,4 @@ idf.py -p /dev/ttyUSB0 monitor
 * Source
 Thanks to [[https://austinmorlan.com/][Austin Morlan]] for his Odroid Go code (MIT license), some of which I have modified. It is kept in Dependencies/embedded-game-programming for reference, but that copy is not used in the app.
 
-I found it much easier to get working than [[https://github.com/OtherCrashOverride/odroid-go-firmware][Odroid-Go-Firmware]] (note: different version of that firmware [[https://github.com/OtherCrashOverride/go-play][here]]).
+I found it much easier to get working than [[https://github.com/OtherCrashOverride/odroid-go-firmware][Odroid-Go-Firmware]] (note: different version of that firmware [[https://github.com/OtherCrashOverride/go-play][here]]). I do use modified subsets of Odroid-Go-Firmware (I'm not sure of the license, so it may actually need to be extracted).

app/src/main.c

@@ -13,7 +13,8 @@
 
 #define ArraySize(array) sizeof((array)) / sizeof((array)[0])
 
-static bool drawBattery = true;
+static bool drawBatteryVoltage = false;
+static bool drawBatteryPercent = true;
 static bool drawTimeSinceBoot = false;
 static bool drawFrameRate = true;
 
@@ -201,6 +202,14 @@ void app_main(void)
 	{
 		memset(gFramebuffer, palette[0], 320 * 240 * 2);
 
+		{
+			float batteryPercentage = Odroid_ReadBatteryLevelPercentage();
+			if (batteryPercentage < 15.f)
+				Odroid_EnableBatteryLight();
+			else
+				Odroid_DisableBatteryLight();
+		}
+
 		int64_t currentTimeMicroSecs = esp_timer_get_time();
 
 		Odroid_Input input = Odroid_PollInput();
@@ -264,11 +273,14 @@ void app_main(void)
 		{
 			if (backlightOn)
 			{
+				// TODO: Tell LCD driver to enter sleep
+				// TODO: Use esp light sleep mode
 				Odroid_BacklightDeinit();
 				waitForSleepActivateRelease = true;
 			}
 			else
 				Odroid_BacklightInit();
+
 			backlightOn = !backlightOn;
 		}
 
@@ -307,14 +319,20 @@ void app_main(void)
 		/* } */
 
 		// Battery
-		if (drawBattery)
+		if (drawBatteryPercent)
 		{
 			char string[10];
-			snprintf(string, ArraySize(string), "B: %d", Odroid_ReadBatteryLevel());
-			/* snprintf(string, ArraySize(string), "B: %02d", Odroid_ReadBatteryLevel()); */
+			snprintf(string, ArraySize(string), "B: %.0f", Odroid_ReadBatteryLevelPercentage());
 			DrawText(gFramebuffer, string, ArraySize(string), 0, 0, palette[3]);
 		}
 
+		if (drawBatteryVoltage)
+		{
+			char string[10];
+			snprintf(string, ArraySize(string), "B: %03d", Odroid_ReadBatteryLevel());
+			DrawText(gFramebuffer, string, ArraySize(string), 0, 3, palette[3]);
+		}
+
 		// Time since boot
 		if (drawTimeSinceBoot)
 		{
@@ -374,8 +392,9 @@ void app_main(void)
 
 		Odroid_DrawFrame(gFramebuffer);
 
+		// Just high enough that button presses feel responsive
 		if (enableLowFrameRate)
-			vTaskDelay(25);
+			vTaskDelay(5);
 
 		lastFrameInput = input;
 	}

app/src/odroid/battery.c

@@ -61,6 +61,16 @@ uint32_t Odroid_ReadBatteryLevel(void)
 	return voltage;
 }
 
+float Odroid_ReadBatteryLevelPercentage()
+{
+	uint32_t voltage = Odroid_ReadBatteryLevel();
+
+	const float FullVoltage = 4.27f;
+    const float EmptyVoltage = 3.5f;
+
+    return ((voltage / 1000.f) - EmptyVoltage) / (FullVoltage - EmptyVoltage) * 100.0f;
+}
+
 void Odroid_EnableBatteryLight(void)
 {
 	gpio_set_level(BATTERY_LED_PIN, 1);

app/src/odroid/battery.h

@@ -5,6 +5,7 @@
 
 void Odroid_InitializeBatteryReader(void);
 uint32_t Odroid_ReadBatteryLevel(void);
+float Odroid_ReadBatteryLevelPercentage();
 void Odroid_EnableBatteryLight(void);
 void Odroid_DisableBatteryLight(void);