Raspberry Pi4 bootloader EEPROM release notesUSB MSD boot also requires updated beta GPU firmware. Please read
https://www.raspberrypi.org/documentation/hardware/raspberrypi/bcm2711_bootloader_config.md2020-07-09 Promote 2020-06-15 to STABLEIncrease port power off limit to 5 seconds.
Increase the port power off default to 1 second. This seems to cover most commonly seen USB MSD devices which require the USB port power to be disabled after the USB HC chip is reset.
Reset activity LED after SPI access to reduce the number of spurious LED flashes.
Add SPI error diagnostic error code (3 long 1 short) if SPI commands timeout. (So far this failure has not been observed on failed boards)