Apparently M5.Display.powerSaveOn() reduces the RGB color space to just a few base colors, I suppose to save PSRAM bandwith and power. As a result all your colors are way off when powersave is on.

The configTime() or configTzTime() functions do not return errors but the returned date and time are way off: up to 2 days in the future and totally wrong time too.

The esp32 code shown in this makernote works without fail on the same Tab5 device.

my platformio.ini:

[env:esp32p4_pioarduino]
platform = https://github.com/pioarduino/platform-espressif32.git#54.03.21
upload_speed = 1500000
monitor_speed = 115200
build_type = debug
framework = arduino
board = esp32-p4-evboard
board_build.mcu = esp32p4
board_build.flash_mode = qio
board_build.partitions = default_16MB.csv
board_build.filesystem = spiffs
build_flags = 
	-DBOARD_HAS_PSRAM
	-DCORE_DEBUG_LEVEL=5
	-DARDUINO_USB_CDC_ON_BOOT=1
	-DARDUINO_USB_MODE=1
lib_deps = 
	https://github.com/M5Stack/M5Unified.git
	https://github.com/M5Stack/M5GFX.git

Other Arduino stuff is broken too: after wakeup from lightsleep the display does not work properly half of the time: the cursor position is sometimes totally off, or sometimes it does not wake at all. I suppose the display needs a hardware reset via a GPIO, but can't find any mention of this in the docs.

But the hardware is very nice indeed. Especially the undocumented coin battery backup for the RTC is a nice surprise!

To make this detection really reliable I had to change the RTC register check like this:

Wire.begin(21, 22);
uint8_t reason = M5.RTC.readReg(0x01);
// now it's safe
M5.begin();
// check reboot reason flag: TIE (timer int enable) && TF (timer flag active)
if ((reason & 0b0000101) == 0b0000101) {
    restartByRTC = true;
    Serial.println("Reboot by RTC");
} else {
    restartByRTC = false;
    Serial.println("Reboot by power button / USB");
}

https://github.com/dheijl/M5Core2MpdCli

My RPI MoodeAudio players do not have a display, so I added a remote one, using the M5Core2, that allows me to:

• load the initial/updated config from SD and save it to flash (NVS)
• select the MPD player from a list if you have more than one player (I do)
• see what's currently playing
• select a favourite radio station from a list of favourites (configured in Moode or not, the url is all that MPD needs)
• stop/start playing

I suppose it would work with any MPD based audio player.