LPC 1820 - GPIO - DMA - SRAM speed

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LPC 1820 - GPIO - DMA - SRAM speed

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lpcware
NXP Employee
NXP Employee
Content originally posted in LPCWare by kellykan on Sat Mar 05 14:02:58 MST 2016

Hi Guys,

I've been working on a project for a while where we implemented a GPIO DMA transfer to memory to capture 2 bit parallel data coming from an ADC at 15.5Mhz. I noticed the captures would go out of sync a couple of kBs in (say 12Kb). I configured the Audio Clock to clock the M3 core at 240Mhz during these transfer to try and speed up the loading of DMA descriptors which seemed to resolve the issue.

Now I'm looking at pushing this a bit further , we have a 22Mhz output from an ADC I want to capture. I've currently tried different options , implementation using one channel with a linked list to fill memory and implementation using two dma channels. Both methods have the dma triggered by the SCT , the SCT is setup to trigger an event on either rising and falling edge of the input clock. In the mode where I try two dma channels I  trigger the first dma channel on the first falling edge and the second on the second falling edge. In the later scenario, I can get the first 40 bytes before losing a byte. In the single dma channel method I loose a byte just as it loads the next descriptor. In this method I transfer about 4K at a time.

So my question is if I have 8 bit parallel data being measured from a gpio port using SCT as the trigger and DMA, how fast could I clock the input data reliably. Or is there a better way of doing this?

Kelly
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lpcware
NXP Employee
NXP Employee
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266 Views
lpcware
NXP Employee
NXP Employee
Content originally posted in LPCWare by kellykan on Sun Mar 06 13:01:01 MST 2016
Id rather try an get it resolved using the current platform if possible and later may look at migrating to a faster platform such as 4320.
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lpcware
NXP Employee
NXP Employee
Content originally posted in LPCWare by starblue on Sun Mar 06 02:25:08 MST 2016
How about using SGPIO on an LPC4320? Then your serial I/O would be a lot less stressful.
Otherwise it should mostly be compatible to the LPC1820, and not much more expensive (~10%).