Part Number: AM6442
I am using USB to implement the DFU (Device Firmware Upgrade) function for the TI AM6442 chip. The DFU supporting tools—including the bootloader image, SBL (Secondary Boot Loader) image, and app image—have been fully validated and work flawlessly on the TI AM6442 EVM development board. However, when using the same software, PC, and USB data cable on my custom PCB (which uses the identical TI AM6442 main chip), an issue arises.
Detailed Symptom
- Both the EVM and the custom PCB can be booted into DFU mode via the bootroom. During the initial USB driver initialization, the PC successfully detects and displays the USB device icon labeled "AM64x DFU" for both boards.
- After flashing the bootloader and executing it:
- The EVM re-enumerates the USB device normally as "AM64x-AM243x-DFU" and completes all subsequent DFU upgrade operations without errors.
- The custom PCB fails: The PC reports "Unknown USB Device (Device Descriptor Request Failed)", and all follow-up DFU operations are aborted.
Custom PCB USB Hardware Details
The USB physical connections on the custom PCB are configured as follows:
- Data lines: SoC_USB0_DP and SoC_USB0_DM are routed from the TI AM6442 chip to the USB Type-C port, with a common-mode choke in series (the choke is slightly larger than that on the EVM evaluation board).
- SoC_USB0_ID: Left floating.
- SoC_USB0_VBUS: Connected to 5V power.
- SoC_USB0_RCALIB: Connected to a 499-ohm resistor.
- SoC_USB0_DRVVBUS: Left floating.
Additional Validations
- EMMC functionality: Verified to work normally with read/write operations at SDR25 speed.
- USB UART mode: The USB interface, when driven as two UART ports, supports bidirectional data transmission/reception correctly.
- The USB hardware packets captured by the sniffer tool will be provided separately for further analysis.
The following sniffer-captured USB packets are obtained when the device is booted into DFU mode and the chip's built-in primary bootloader is launched. Although both the EVM development board and the custom PCB can drive the USB device (which is recognized as "AM64x-DFU" on the PC), the specific USB packets captured from the two boards are different.
The USB packets of the EVM evaluation board are as follows:
The USB packets of the custom PCB are as follows:
