I recently had a sopine module start to fail on me. The symptom was most boots would fail partway through the boot. It would just stop, serial console output stops, the board powers off. Note that this is identical to lower power but in this case was not (I have multiple sopine modules and work with them daily).
I successfully mitigated this issue by underclocking. Specifically I did three things:
Underclocking in U-Boot
I added the following line to `/boot/boot.cmd` and compiled the file:
mw 0x1c20000 0x80000900
Per the Allwinner A64 manual (p84), this sets the CPU to the lowest clock speed possible: 240MHz.
The formula used to set the clock speed is `(24Mhz*N*K)/(M*P)`. The high bit switches should always be the same, and the low bits used in the formula are padded to align to hexadecimal digits. This yields the following map for the formula: `0x800PNNKM` with a max value of `0x80031F33`.
Underclocking in the kernel
The easiest way to do this is set `CONFIG_CPU_FREQ_DEFAULT_GOV_POWERSAVE=y`. The powersave governor operates the cpu at the lowest clockspeed possible.
If you disable all userspace cpu frequency utils, you can stop here. Alternatively, you may skip this step and just do the following.
Set powersave governor in /etc/init.d/cpufrequtils
Here's a oneliner that does this:
sed -i 's/^GOVERNOR=.*/GOVERNOR="powersave"/' /etc/init.d/cpufrequtils
After underclocking, the sopine module has been operating fine. If you are installing A64 chips in the field that don't require high performance, you can use this to enable a longer device life.
