I replace the old 2.2mm tall SPI flash and put a new 1.0mm tall SPI flash to VoCore, but then I find I can not update u-boot or firmware.
There are the command:

wget http://vonger.cn/upload/uboot.img
mtd write uboot.img u-boot

Looks like it works smoothly, no error reported.
But after I reboot VoCore, it is still the old version…
I thought that must be my mistake, I uploaded the wrong version of the uboot, so I just do the wget/mtd again.
Unfortunately, it is still the old version and even worse, the UART outputs some random code sometimes.

That really scared me 🙂 I was thinking: is that caused by the hot summer? Outside is over 35℃, VoCore is about 68~70℃. But somebody had tested, RT5350 could work normally even over 90℃,  so we can exclude this possibility.

The second guess is about software. I tried the same thing and compared it with another VoCore, that one works well.

So I confirm that is hardware problem, especially on the SPI flash part. At that time, I remember there is a pin named WP(write protect) on the SPI flash. That pin must be driven to high(3.3V) or the SPI flash will not be able to write(randomly).

Then I put some paste on the pins and solder the 8 pins again, make sure every pin is well connected, then plug VoCore to power, everything is back to normal. 😀