The difference between those ideas is that "Frozen Cache" plays games with the CPU cache to attempt to keep keys entirely in cache and out of DRAM, where TRESOR runs AES entirely out of registers. The downside of the "Frozen Cache" approach is that X86 doesn't give you enough control over the cache to provide assurance that keys aren't touching RAM.
The difference between those ideas is that "Frozen Cache" plays games with the CPU cache to attempt to keep keys entirely in cache and out of DRAM, where TRESOR runs AES entirely out of registers. The downside of the "Frozen Cache" approach is that X86 doesn't give you enough control over the cache to provide assurance that keys aren't touching RAM.