How to expand the 256MB access for DDR2 ?

Mário,

The OMAP-L138 does not provide multiple chips selects to allow you to use multiple devices. It only accesses a total range of 256MB from the DDR2 EMIF. And the pin loading is critical for DDR2 access to succeed, so you must limit the design to what is shown in the Data Manual, which is 1 2Gb x16 memory or 2 1Gb x8 memories.

One way to get more memory available would be to build a mechanism through an FPGA to allow you to access more memory in pages through the EMIFA SDRAM interface. This would be a difficult design to do, though.

Another way would be to pair the additional 2Gb DDR2 modules with additional AM1808 or C6748 or OMAP-L138 devices, as required, to get the memory space you need, then allow those additional processors to communicate over a shared EMIFA bus or some other method. This would depend on the use you have for the extra memory space - active processing or data storage.

The best way would be to move to a newer processor that supports much more external memory. I would recommend the AM3358, the AM4376, the AM5728, and the C6655.

Regards,
RandyP