I wrote a simple memtest that automatically cycles through various possible dram controller clocks and that can do tests over the entire DRAM address space:
https://megous.com/git/p-boot/log/?h=memtest
It probably doesn't give enough time to testing the memory at each frequency point, but it's easy to patch to do longer runs of tests.
It can be used the same way u-boot can be used. Replace u-boot with it at 8KiB offset on the SD card and reboot. Serial console access is needed to view the results/progress.
https://megous.com/git/p-boot/log/?h=memtest
It probably doesn't give enough time to testing the memory at each frequency point, but it's easy to patch to do longer runs of tests.
It can be used the same way u-boot can be used. Replace u-boot with it at 8KiB offset on the SD card and reboot. Serial console access is needed to view the results/progress.