Each time a bit operation of some global variable is done before DMA is started, the DMA forward int

ALOONG — Wed, 19 Mar 2025 11:54:01 GMT

I am in the use of LPC4370 microcontroller HSADC+DMA, if each time in the DMA before do some global variable bit operations, each DMA into the interrupt time will be longer, do not know what is the reason, do not have brothers know?

My code：

void DMA_IRQHandler(void)
{
if(LPC_GPDMA->INTSTAT & (1UL << 7))
{
LPC_GPDMA->INTTCCLEAR |= (1UL <<7);
LPC_GPIO_PORT->B[0][13] = false;
ucColletStop = 1;
}
}

int main(void)
{

SystemCoreClockUpdate();

Chip_GPIO_SetPinDIROutput(LPC_GPIO_PORT, 0, 13);
Chip_GPIO_SetPinState(LPC_GPIO_PORT, 0, 13, false);

HsadcInit();
DmaInit();

for(uint32_t i = 50000000; i > 0; i--){__asm("nop");}//1s
LPC_GPIO_PORT->B[0][13] = true;
Chip_HSADC_SWTrigger(LPC_ADCHS);

while(1)
{
if(ucColletStop == 1)
{
ucColletStop = 0;

for(uint32_t i = 1000000; i > 0; i--){__asm("nop");}//20ms

Chip_HSADC_SetActiveDescriptor(LPC_ADCHS, 1, 0);//Stop HSADC
Chip_HSADC_SWTrigger(LPC_ADCHS);

for(uint32_t i = 1000000; i > 0; i--){__asm("nop");}//20ms

for(uint16_t i = 0; i < 1024; i++)
{

ulConvertedData[2*i] = dma_buffer[i]&0xFFF;
ulConvertedData[2*i+1] = (dma_buffer[i]>>16)&0xFFF;
}

for(uint32_t i = 1000000; i > 0; i--){__asm("nop");}//20ms

Chip_HSADC_SetActiveDescriptor(LPC_ADCHS, 0, 1);//Start HSADC
CollectStart();//Start DMA
Chip_HSADC_SWTrigger(LPC_ADCHS);

LPC_GPIO_PORT->B[0][13] = true;
}

}

}

Re: Each time a bit operation of some global variable is done before DMA is started, the DMA forward

Alice_Yang — Mon, 24 Mar 2025 10:24:09 GMT

Hello @ALOONG

a bit operation of some global variable (e.g., var |= 0x01) may trigger multiple Read-Modify-Write operations. If the DMA is accessing the same memory region (e.g., the ADC buffer) during this time, the CPU and DMA will contend for the bus, resulting in bus arbitration delays.
Check the DMA interrupt priority to ensure it is higher than other non-real-time tasks。

Alice

LPC MicrocontrollersのトピックEach time a bit operation of some global variable is done before DMA is started, the DMA forward int

Each time a bit operation of some global variable is done before DMA is started, the DMA forward int

Re: Each time a bit operation of some global variable is done before DMA is started, the DMA forward