again, thanks for your clues to this problem. I don't think post code 0x52 is about memory configuration. The post code appears when I call TempRamInit which is supposed to enable Cache-as-RAM. Real memory is initialized at a later call to FspMemoryInit. coreboot supplies the location of the microcode and a cachable region to TempRamInit. Additionally, there are some settings that can be applied to the FSP image with Intel's Binary Configuration Tool. I don't know if these are used during TempRamInit, but I'll try and fiddle around with them.
I agree, it would be helpful to have a list of post codes that can be output by FSP. Otherwise it's all speculation as what is wrong.