Hello folks,
Those who are interested in using DMA (Direct Memory Access) on LPC1768 mbed boards with Mbed OS 6 please find a fork of Andy Kirkham’s MODDMA library here.
Below is an example of comparing DMA speed with memcpy.
#include "mbed.h"
#include "MODDMA.h"
DigitalOut led1(LED1);
MODDMA dma;
int transferState = 0;
Timer timer;
// Create a source buffer we are going to move.
static char src[16*1024-1] __attribute__((section("AHBSRAM0")));
// Create a buffer for the destination to copy to.
static char dst[sizeof(src)] __attribute__((section("AHBSRAM1")));
/**
* @brief
* @note
* @param
* @retval
*/
void myCallback(void)
{
transferState = 1;
}
/**
* @brief
* @note
* @param
* @retval
*/
int main()
{
timer.start();
// Transfer/copy src content to dst using the memcpy function
memcpy(dst, src, sizeof(src));
timer.stop();
printf("It took %lli us to transfer %i bytes using memcpy\r\n", timer.elapsed_time(), sizeof(src));
// Create a MODDMA configuration object.
MODDMA_Config* conf = new MODDMA_Config;
// Setup that configuration
conf->channelNum(MODDMA::Channel_0);
conf->srcMemAddr((uint32_t) & src);
conf->dstMemAddr((uint32_t) & dst);
conf->transferSize(sizeof(src));
conf->transferType(MODDMA::m2m);
conf->attach_tc(&myCallback);
// config end
// Pass the configuration to the controller
dma.Setup(conf);
timer.reset();
timer.start();
// Tell the controller to perform the DMA operation
// defined by that configuration.
dma.Enable(conf);
while (transferState == 0); // wait for DMA transfer to be completed
timer.stop();
printf("It took %lli us to transfer %i bytes using DMA\r\n", timer.elapsed_time(), sizeof(src));
while (1) {
led1 = !led1;
ThisThread::sleep_for(500ms);
}
}
Printout:
It took 1204 us to transfer 16383 bytes using memcpy.
It took 96 us to transfer 16383 bytes using DMA.