LPC2478 versus LPC1788

[JeGy]

Hi,
I have a project running on a LPC2478, similar to the LPC2478-STK (a subset of the LPC2478-STK). It runs at 72MHz.

The size of my code is approaching the 500k limit, so I have tried to cross load the code from a serial flash to external SD-RAM and execute the code from the external SD-RAM.
In this way my code can exceed the 500k limit.

Unfortunately, the execution speed is slower when running from the SD-RAM. It runs app. tree times slower.
The speed reduction comes probably because the LCD also uses the SD-RAM, and therefore occupies the bus, resulting in reduced access speed for normal read/write operations.

Does anybody here or at Olimex know if the LPC1788 have similar speed reduction on executing code from the external bus?

Thanks in advance!
Regards Jens

[LubOlimex]

Hey Jens,

You have answered the question yourself actually.

Code Select Expand

The speed reduction comes probably because the LCD also uses the SD-RAM, and therefore occupies the bus, resulting in reduced access speed for normal read/write operations.


The LPC1788 is considerably faster and better than LPC2478 but it would probably yield only little difference in the SD-RAM communication speed.

Best regards,
Lub/OLIMEX

[JeGy]

Hi,

thank you, I hoped that someone had done the test for me  , so I better could evaluate if I should use the 1788 i my next generation of the product.

I also hoped that NXP perhaps had done some HW improvements about the slower SD-RAM acces when a LCD is applied

Regards Jens