Allwinner A133 (Pritom K7 tablet): USB bulk timeout (error 7)

[Wellington2018]

Hello everyone,

I'm facing a persistent timeout issue during bulk USB transfer (Error 7) when trying to interact with an Allwinner A133 SoC using sunxi-fel.

Device Details:
Pritom K7 Tablet
SoC: Allwinner A133 (AArch64)
Status: Bootloader unlocked.

The device is currently in a boot loop and cannot natively enter Fastboot mode. It successfully enters FEL mode (active BROM).

Backups: I have full backups of the available partitions extracted via ADB.

The Problem:
Whenever I try to send an SPL/U-Boot image to RAM, the transaction starts, the USB bus freezes, and sunxi-fel terminates the connection with a timeout error. Here's a representation of the error I'm receiving:

$ ./sunxi-fel ver
usb_bulk_send() ERROR -7: Operation timed out

What I've already tried:
USB ports and cables: I tested on dedicated USB 2.0 ports.

Different SPLs: I tried both a mainline U-Boot SPL and other U-Boot SPLs for the A133, and even so, they cause the USB connection to drop during execution.

Observations:
UART: so far I've only found the DEBUG_UART on the board, but it only emits low-level telemetry from the AR100 coprocessor at 57600 baud.

My goal:

1. Successfully load a basic U-Boot/Fastboot environment into RAM via FEL to write a backup of the env_a partition (which was corrupted during testing). 2. Or use sunxi-fel mmc write safely, if there is a known stable offset/method for the A133, to completely bypass code execution in RAM.

Has anyone managed to stabilize the FEL protocol on the A133 SoC after the DRAM initialization phase? Any patches, environment overrides (such as AW_USB_MAX_BULK_SEND) or workflows specific to this chip family would be greatly appreciated. Thank you in advance!

(If there are any errors, please forgive me as it was translated from Portuguese.)

[apritzel]

Hi, even though this is not the right repo to complain about (it should be linux-sunxi/sunxi-tools instead):

Whenever I try to send an SPL/U-Boot image to RAM, the transaction starts

What do you do, exactly, for that? Using sunxi-fel's uboot or spl command? Please note that you need a board specific SPL build for this to work, to initialise the DRAM correctly. Just taking some other board's parameters will most likely not work, the SPL will bail out, not return to the BROM's FEL code, resulting in the USB device's disappearance. So if you just use the spl command, does that return? And if yes, can you access the DRAM afterwards? Just try: sunxi-fel -v write 0x40000000 somefile.ext.

Since you have the BSP image available, you can try to extract the DRAM parameters with the sunxi-fw tool, then creating a new defconfig file for your tablet with those parameters.
There is a bit more than that, but that would be a start. But even if you get the SPL started, there is no easy way to restore the BSP image, if that is what you are after. Allwinner's phoenix-suite would probably be better suited for that.