August 11, 2022, 03:43:08 pm

LPC2478 versus LPC1788

Started by JeGy, February 14, 2013, 10:57:53 pm

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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.

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
Technical support and documentation manager at 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