In-cache stack in MPC5674F (vs. MPC5777C)

[ricardofranca]

Hello,

I followed AN5191 to set a MPC5777C board up and, for a given application, noticed a sizeable performance gain (~10%) when the stack was inside the data cache, rather than the internal SRAM. I tried to repeat the experiment with a MPC5674F board and had no gain at all - in fact, I got a slight performance loss of ~3%.

Is this expected? I supposed gains might be smaller because the MPC5674F internal SRAM has a smaller latency than the MPC5777C one, but I did not expect to see a negative result.

Both boards are running at 264MHz.

Thanks,

Ricardo

[lukaszadrapa · Accepted solution]

Hi @ricardofranca 

"because the MPC5674F internal SRAM has a smaller latency than the MPC5777C one" - this is the key point. The stack in cache can help significantly on MPC5777C because of the mentioned latency. This effect won't be so visible on MPC5674F. I guess that the performance loss can be caused by fact that the size of cache used for application is smaller, so more flash reads are needed in runtime.

Regards,

Lukas