We are trying to decide on whether to use ARM7 or ARM9 core in a ASIC design. One major consideration is system power consumption. From what I am told, the ARM9 consumes twice as much power as the ARM7, but most of this extra power is used by the cache. It is hard to believe that the cache controller consumes this much power, so I have to assume that the cost includes the power used by the memory accesses to the cache memory itself, and that the power figure for the ARM7 does not include the cost of accessing memory (even on chip memory).
If this is true, then the additional power cost of the ARM9 might be almost negligible in a real system.
The advantages of having a cache are potentially quite substantial in terms of simplifying our software design, since otherwise we have to carefully tailor our OS/application memory layout to run out of internal memory for the bulk of operations, while running out of external memory for setup, housekeeping, file system operations, etc. Essentially, we would have to implement a manual static "cache" using internal memory.
Does anyone out there know about these sorts of design tradeoffs on the ARM platform? Does anyone know more about how the ARM power consumption numbers are calculated?
Thanks in advance for any help!
- Andy Voelkel