06-25-2020, 08:25 PM
Yeah, you need a UART to troubleshoot further, then.
The reason the light doesn't come on with nothing on the eMMC and no SD card is because the firmware (loaded from eMMC or SD card) is what turns that light on.
There's a tiny bit of boot ROM in the system that looks on the SPI (hazardous to mess with - quite the pain to recover if you screw it up), the eMMC, then the SD card for the firmware files at the proper offsets. That firmware handles turning on the LED, general system bringup, and booting from, by default, the SD card then the eMMC. If you've got a bad firmware on the eMMC, the system won't progress to booting from the SD card (until you turn the switch off).
Serial will illuminate the problem. You don't have a 3.3V TTL USB to serial adapter and a spare 3.5mm stereo cord laying around? That's what I built mine from...
The reason the light doesn't come on with nothing on the eMMC and no SD card is because the firmware (loaded from eMMC or SD card) is what turns that light on.
There's a tiny bit of boot ROM in the system that looks on the SPI (hazardous to mess with - quite the pain to recover if you screw it up), the eMMC, then the SD card for the firmware files at the proper offsets. That firmware handles turning on the LED, general system bringup, and booting from, by default, the SD card then the eMMC. If you've got a bad firmware on the eMMC, the system won't progress to booting from the SD card (until you turn the switch off).
Serial will illuminate the problem. You don't have a 3.3V TTL USB to serial adapter and a spare 3.5mm stereo cord laying around? That's what I built mine from...
