DMA ADC sync

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DMA ADC sync

NXP Employee
NXP Employee
Content originally posted in LPCWare by rouxfederico on Sat Jul 12 10:03:52 MST 2014
Hello, this is my first post here. I always find the answer to my programming problems but I haven't found for this.

The problem is with the LPCOpen example periph_adc, so there's no need to upload the project.In the function App_DMA_Test is written:

static void App_DMA_Test(void)
uint16_t dataADC;

/* Initialize GPDMA controller */
/* Setting GPDMA interrupt */
NVIC_SetPriority(DMA_IRQn, ((0x01 << 3) | 0x01));
/* Setting ADC interrupt, ADC Interrupt must be disable in DMA mode */
/* Get the free channel for DMA transfer */
dmaChannelNum = Chip_GPDMA_GetFreeChannel(LPC_GPDMA, _GPDMA_CONN_ADC);
/* Enable burst mode if any, the AD converter does repeated conversions
   at the rate selected by the CLKS field in burst mode automatically */
if (Burst_Mode_Flag) {
Chip_ADC_SetBurstCmd(_LPC_ADC_ID, ENABLE);
/* Get  adc value until get 'x' character */
while (DEBUGIN() != 'x') {
/* Start A/D conversion if not using burst mode */

if (!Burst_Mode_Flag) {
channelTC = 0;
Chip_GPDMA_Transfer(LPC_GPDMA, dmaChannelNum,
  (uint32_t) &DMAbuffer,

/* Waiting for reading ADC value completed */
while (channelTC == 0) {}

/* Get the ADC value fron Data register*/
dataADC = ADC_DR_RESULT(DMAbuffer);
/* Disable interrupts, release DMA channel */
Chip_GPDMA_Stop(LPC_GPDMA, dmaChannelNum);
/* Disable burst mode if any */
if (Burst_Mode_Flag) {

I've some problems with this code:

  [*] DMA transfer is not sync with the ADC conversion. I've found that the DMA transfer the result from ADGDR before the ADC makes the conversion. It's only sync the first time. If you put a breakpoint in the line Chip_ADC_SetStartMode(...) (that's inmediately before starting the ADC conversion) and you change the input voltage from, for example, 0V to 1V, the DMA transfers a 0x00 from the last conversion of 0V, and then, the subsequents conversions are OK. Why is this?

[*] In the User Manual (UM10360 page 618. Table 567) says:

Transfer Direction :  Peripheral-to-memory 
Request Generator : Peripheral 
Flow Controller : DMA Controller

Reading this, I understand that when you config a P2M DMA transfer, the request generator and the flow controller are fixed to these I read in the table.
So, in the LPCOpen function, why you have [color=#30f]GPDMA_TRANSFERTYPE_P2M_CONTROLLER_DMA[/color] and [color=#30f]GPDMA_TRANSFERTYPE_P2M_CONTROLLER_PERIPHERAL [/color]transfer type? I've read all the function that uses this constants and there's no difference between them. The switch/case uses both constants to do the same things. But I still have a problem, when I put transfer type to [color=#30f]GPDMA_TRANSFERTYPE_P2M_CONTROLLER_PERIPHERAL[/color], the DMA returns an ERROR from the ISR handler.

Well, that's all!
I'll be waiting anxious for the answer :).
Thank's a lot and sorry for my English.

Labels (1)
2 Replies

NXP Employee
NXP Employee
Content originally posted in LPCWare by rouxfederico on Thu Jul 17 06:53:52 MST 2014
Ok thanks! I'll try it by hand instead of using LPCOpen library.
If I make it work, I'll post here the program.
Thanks again,

NXP Employee
NXP Employee
Content originally posted in LPCWare by wmues on Sun Jul 13 02:47:18 MST 2014
Hmmm... for my LPX1788 mmc driver, I had to do the DMA programming "by hand", because the software provided from NXP has not covered the right DMA programming bits for the mmc peripheral.

IMHO, these thin wrappers to IP functions are nearly worthless. They lack a level of abstraction. For me, it's better to do it by hand.


PS: the user manual from NXP is good. Most items are covered here.