DMA and GPIO speed ?

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DMA and GPIO speed ?

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lpcware
NXP Employee
NXP Employee
Content originally posted in LPCWare by Pacman on Sat Nov 09 11:57:31 MST 2013
I've tried using the DMA to output data on the GPIO.

Unfortunately, it seems I can only get it to change pin state 24000000 times per second.
I've tried synchronizing to Timer0 at 204MHz, but if I set Match Register 0 to less than 18, the frequency does not increase.

If I disable synchronizing, I can reach 24M by using AHB Master 1 for destination and AHB Master 0 for source.

But I can't seem to get it faster than that. (And I can't seem to do memory-to-memory transfers on GPIO pins with AHB Master 0)

The LPC1768 can go much higher, probably because you don't have to choose an AHB Master.

Has anyone gone beyond that 24M outputs per second using the DMA ?
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kaiyuewang
Contributor I

Hello, I am just trying to do the same thing in the LPC54114  board. 

And in the <user manual> , it says: Effective processing of the externally supplied clock to the counter has some limitations. Since two successive rising edges of the APB bus clock are used to identify only one edge
on the CAP selected input, the frequency of the CAP input cannot exceed one half of the
APB bus clock. 
So perhaps you should try to improve your the frequency of your CPU (to 96MHz for example).

But I have encountered other problems: I have used the Burst Mode of DMA, which is triggered by Timer3. But it seems that when the frequency of Timer3 is greater than 3MHz, the DMA can not catch this speed. 

Can you help me? Thank you.

 
 

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