TMS570LS3137 performance drop when executing from external memory

Hi Christophe,

  Running code from SDRAM is expected to take many more cycles than running from internal memory. Normally fetching one 32-bit instruction from internal RAM takes just one cycle. Fetching a 32-bit instruction from flash memory is also 1 cycle if the code is sequential since the flash controller is built with an internal prefetch buffer to prefetch the subsequent sequential instructions in advance. The flash and SRAM are tightly coupled to the CPU for fast access. 

  Running code from EMIF means the CPU needs to fetch the data via its Level 2 AXI interface and then through the on-chip interconnect before reaching to the EMIF interface. This can take some cycles to send the command to the EMIF. In addition, the EMIF interface is only 16-bit. If you have a 32-bit instruction or data to read then it needs to take two 16-bit EMIF accesses to complete. 

  In my opinion running code from SDRAM is not suitable for LS31x device if you are performance critical. SDRAM is more suitable for data storage. In our LC4357 device with the on-chip cache, running code from SDRAM will have minimal impact to the performance since the code will be cached. As long as you have a cache hit, the access to the instructions and data will be one cycle. 

Hi Charles,

You recommend to use the LC4357 device instead of the LS3137 on the previous case. I have some questions about them:
- Are these two devices built using the same technology?
- The 4357 device is not yet ACTIVE, can you explain me why? Is it still under qualification? I read on another thread that you expect it to become active on September, is it still correct?

Regards,

MCV