We have a number of new custom boards based on the imxRT1021 EVK kit.
The customization sets BOOT_MODE[1:0] pins to 00. We recognize that this results in "Boot From Fuses" mode, and that factory-fresh RT1021 will have the BT_FUSE_SEL =0, which should result in the bootROM running Serial Downloader.
For some units, we can communicate over UART1, and get BT_FUSE_SEL set. For others, we are unable to make serial communication. We can still attach over JTAG/SWD and see the program counter moving around the 0x200000 range, which implies bootROM is live, but we don't know why it won't respond over UART1. We can even configure and program serial NOR flash over flexSPI, but unable to set BT_FUSE_SEL to 1, bootROM won't jump over to it.
Using oscilloscope probes on the UART1 pins (GPIO_AD_B0_07), we verify serial data pulses at the MCU's Rx pin, but there is no activity coming out on its Tx pin (GPIO_AD_B0_06).
Is there any memory location we can look at using the JTAG/SWD that would give us a hint to what the Serial Download is doing? For example, an exception vector, or a flag that indicates it has settled on USB comms instead of UART, or other information that would prove that bootROM is actually executing the Serial Download program at all?
[Alternatively, a white paper or document describing how to program BT_FUSE_SEL by direct register manipulation over JTAG, without the use of UART1 or USB comms would also be useful].
