Using Emac CPPI RAM for Buffer Descriptors

Hi Oscar,

What software are you using?

Hi Biser,

I'm not using any 3rd party software.  The Ethernet driver I'm using was written from scratch based on reading the Technical Reference Manual.  Is there a special initialization step I'm missing that is necessary in order to use the local EMAC RAM for the descriptors?

I did read section 22.2.5 of the TRM.  As far as I can tell the descriptors are initialized just as described, but there is still an error.  The TRM does not appear to state that anything should be initialized differently if using the local EMAC RAM versus using other on/off chip memory like SRAM.  Everything works fine when I use SRAM, so what could be different about using EMAC RAM?

Did you implement this requirement (section 22.2.5.2):

After an EMAC reset and before enabling the EMAC for send and receive, all 16 head descriptor pointer registers must be initialized to 0.

Yes, that requirement is implemented.  All 16 HDP registers are initialized to 0.

I figured out what was wrong.  The manual says "The base address of CPPI descriptors is 5C02 0000h. The 8K bytes of CPPI memory begin at address 01E2 0000h from the EMAC perspective.".  So I just translated the pointers passed to the HDP registers, and all next pointers in the CPPI descriptors, to be in the EMAC address space instead of keeping the pointers in the local address space.  Looks like this translation is only necessary when using the EMAC memory, and is not needed when using other on/off chip memory.