topic Re: LPC1768 accumulate two ADC channels every 1ms in LPC Microcontrollers

LPC1768 accumulate two ADC channels every 1ms

kiryat8 — Thu, 15 Mar 2018 07:48:58 GMT

I would like to continuously read two ADC channels once every 1ms accumulating 500 values of each channel and perform a calculation every 500ms. I usually at slower speeds just use the ADC interrupt but this looks like a good candidate for DMA or DMA with a timer. What is the best way to do this? Does anyone have a step by step code example?

I would like to set the DMA source as the ADC, but the trigger to start a single ADC read f two of its channels from the timer.

When 500 readings x 2 have finished I expect the DMA interrupt to which I would restart the process but switching between two sets of 500 x 2 ADC values.

How do I configure the DMA to do this?

I guess transferring a single ADC reading is a 32 bit value even though the ADC is only 12bits.

So I would need 500x2x4x2 = 8000 ram bytes.

Any help or suggestions would be appreciated.

Re: LPC1768 accumulate two ADC channels every 1ms

Dezheng_Tang — Thu, 15 Mar 2018 16:59:12 GMT

Check out some of the old examples to see if it helps. There is a ADC DMA example:

http://host.lpcware.com/content/nxpfile/mcb1700-sample-code-bundle-lpc17xx-peripherals-using-keils-mdk-arm

Re: LPC1768 accumulate two ADC channels every 1ms

kiryat8 — Sun, 18 Mar 2018 04:37:07 GMT

Thank you but I have read the Keil examples but can not see a way to use DMA to be efficient when I need to sample two consecutive ADC channels. The transfer width is 32 bits for a single ADC reading and there is no way I can see to set it to 64 bit for two readings without using the increment source option. To use the increment source option would mean I would have to set the data transfer to 2 readings and get an interrupt reset the source pointer. This is more code and adds complexity and does not seem to have a real advantage over using the CPU to read the ADC reading and trigger another reading every 1ms.

Is there any other way?