Titan SoC
The SPA504G uses the Texas Instruments TNETV1057ZDW processor on a Titan SoC, pictured below.
It is super hard to find a datasheet for this CPU/SoC; however, the boot logs reveal that the CPU operates at 87.5 MHz, and the SoC features 60 KB (61.44 KiB) of memory.
Extra memory banks are provided on the SPA504G's PCB. These are detailed here.
This CPU uses a MIPS instruction set.