rk3288开发板使用RK的SDK无法进入loader模式

sheqw

使用RK的firefly版本的linux SDK，地址见http://opensource.rock-chips.com/wiki_Uboot
For firefly-rk3288 board. Use below command to build the U-Boot:
./make.sh firefly-rk3288

加载后可正常启动，但是怎么都进入不了loader烧录模式，串口log如下：
U-Boot 2017.09-01495-g3a06149 (May 16 2018 - 15:55:01 +0800)
Model: Firefly-RK3288
DRAM:  2 GiB
Relocation Offset is: 7ef6a000
MMC:   dwmmc@ff0c0000: 1, dwmmc@ff0f0000: 0
In:    serial
Out:   serial
Err:   serial
Model: Firefly-RK3288
fastboot key pressed!
Setting reboot to fastboot flag ...
switch to partitions #0, OK
mmc0(part 0) is current device
download key pressed, entering download mode...
RKUSB: LUN 0, dev 0, hwpart 0, sector 0x0, count 0x1d1f000
### ERROR ### Please RESET the board ###

跟踪代码是udc_enable的时候hang（）了，原因不明，应该是uboot有bug，请问如何解决？多谢！