Hi,
I'm triying to use the DWT->CYCCNT in a low level manner. But it seems to now work and I don't really understand why. I'm using the nRF52840 DK and the program looks something like this:
#define TX_PIN NRF_GPIO_PIN_MAP(0, 6)
#define RX_PIN NRF_GPIO_PIN_MAP(0, 8)
#define RTS_PIN NRF_GPIO_PIN_MAP(0, 5)
#define CTS_PIN NRF_GPIO_PIN_MAP(0, 7)
#ifndef NRFX_DELAY_MS
#define NRFX_DELAY_MS(_ms) NRFX_DELAY_US(_ms * 1000)
#endif
static const nrfx_uart_t UART0 = NRFX_UART_INSTANCE(0);
int _write(int handle, char *data, int size )
{
(void)handle;
nrfx_uart_tx(&UART0, data, size);
return size;
}
static void on_clock_event(nrfx_clock_evt_type_t event)
{
(void)event;
}
/** Read cycle counter register */
uint32_t dwt_cyccnt_get(void)
{
return DWT->CYCCNT;
}
/** Reset cycle counter */
void dwt_reset(void) {
DWT->CYCCNT = 0;
}
/** Enable cycle counter */
void dwt_enable(void) {
DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk;
}
/** Disable cycle counter */
void dwt_disable(void) {
DWT->CTRL &= ~DWT_CTRL_CYCCNTENA_Msk;
}
/** TRCENA: Enable trace and debug block DEMCR (Debug Exception and Monitor Control Register */
void dwt_init(void) {
CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
}
static inline void busy_loop(void) {
volatile size_t foo = 0;
for (size_t i = 0; i < (UINT32_MAX / 128); i++)
{
foo += i;
}
}
int main()
{
nrfx_uart_config_t uart_cfg = NRFX_UART_DEFAULT_CONFIG(TX_PIN, RX_PIN);
uart_cfg.pselcts = CTS_PIN;
uart_cfg.pselrts = RTS_PIN;
if (NRFX_SUCCESS == nrfx_uart_init(&UART0, &uart_cfg, NULL)
&& NRFX_SUCCESS == nrfx_clock_init(on_clock_event))
{
nrfx_clock_start(NRF_CLOCK_DOMAIN_LFCLK);
printf("enter\n");
for (size_t i = 0; i < 3; i++)
{
printf("--- ---\n");
dwt_reset();
dwt_enable();
busy_loop();
dwt_disable();
printf("%lu\n", dwt_cyccnt_get());
dwt_reset(); // this does not work at all :(
printf("%lu\n", dwt_cyccnt_get());
}
printf("exit\n");
}
while (true)
{
__WFE();
}
return 0;
}
