Fail to flash aosp image to dragonboard845c

I have bought a new DragonBoard 845c to run AOSP. And I have successfully flashed the devices and entered fastboot mode following this instruction (https://www.96boards.org/documentation/consumer/dragonboard/dragonboard845c/installation/board-recovery.md.html).
The output is as follows:

cliff@cliff-lab:~/Downloads/dragonboard-845c-bootloader-ufs-aosp-41$ 
sudo ../qdl/qdl prog_firehose_ddr.elf rawprogram?.xml patch?.xml
...
partition 1 is now bootable
LOG: INFO: Calling handler for power
LOG: INFO: Will issue reset/power off 100 useconds, if this hangs check if watchdog is enabled
LOG: INFO: bsp_target_reset() 0

cliff@cliff-lab:/media/cliff/93a85f64-b831-40b6-bbab-2c208df42999$ fastboot devices 
a2c48e07	fastboot

However, when I try to flash AOSP images, it fails.

cliff@cliff-lab:/media/cliff/93a85f64-b831-40b6-bbab-2c208df42999$ 
./device/linaro/dragonboard/installer/db845c/flash-all-aosp.sh
android out dir:./device/linaro/dragonboard/installer/db845c/../../../../..//out/target/product/db845c
target didn't report max-download-size
sending 'partition:0' (44 KB)...
FAILED (command write failed (Success))
finished. total time: 0.000s
< waiting for any device >

And when I use command “fastboot devices” again, there is no output, which means the host cannot detect any fastboot device.
What should I do now? Thanks.

can you please share the output on the serial console as well?

Thank you. I have already solved this problem with a USB hub.
It seems that there are some problems with my hardware driver.
The problem is the same as this link: https://forum.xda-developers.com/redmi-note-5-pro/help/help-press-key-to-shutdown-fastboot-t3816021

that’s what I wanted to confirm. We are aware of a bug in this context, and I don’t think your hardware is at fault. It’s a bug in the USB driver in the target side firmware (XBL), which is proprietary. The bug was reported to Qualcomm and the board vendor, an updated firmware exists , but has yet to be released publicly…

Glad that you sorted it out.