nRF 52832 Timer Interrupt and Frequency adjustment

[PoojaK]

Hello,

I need my timer to work at 9600 bps frequency. So accordingly my frequency is 16MHz and to get 9600 Hz I calculated the prescaler to be 10.7 ~ 11. But in the timer code (pca10040) I couldnt find any provision to set the prescaler as required. I see there are only 10 fixed frequency values for the prescaler. So how to I get my timer to work at 9600 bps along with its interrupt (IRQ handler ) ?

These are the prescaler values I am talking about

/**
* @brief Timer prescalers.
*/
typedef enum
{
NRF_TIMER_FREQ_16MHz = 0, ///< Timer frequency 16 MHz.
NRF_TIMER_FREQ_8MHz, ///< Timer frequency 8 MHz.
NRF_TIMER_FREQ_4MHz, ///< Timer frequency 4 MHz.
NRF_TIMER_FREQ_2MHz, ///< Timer frequency 2 MHz.
NRF_TIMER_FREQ_1MHz, ///< Timer frequency 1 MHz.
NRF_TIMER_FREQ_500kHz, ///< Timer frequency 500 kHz.
NRF_TIMER_FREQ_250kHz, ///< Timer frequency 250 kHz.
NRF_TIMER_FREQ_125kHz, ///< Timer frequency 125 kHz.
NRF_TIMER_FREQ_62500Hz, ///< Timer frequency 62500 Hz.
NRF_TIMER_FREQ_31250Hz ///< Timer frequency 31250 Hz.
} nrf_timer_frequency_t;

[Sigurd]

Hi,

How often the TIMER will generate an interrupt depends on the prescaler, and the value set in the Capture/Compare register (CC[x]). From the TIMER chapter in the PS, we have that, "A COMPARE event is generated when the Counter is incremented and then becomes equal to the value specified in one of the capture compare registers."

PoojaK said:

9600 bps

You want to generate an interrupt 9600 times each second? If yes, could you explain the use-case, and what you are planning to do in the interrupt handler ?

[PoojaK]

I want the interrupt at the frequency of 9600 Hz and not 9600 times each second. So basically I want an interrupt after every 1/9600 seconds. I am trying to implement software uart using GPIOs. 

[Sigurd]

Ok, the closest would then be prescaler set to 0, and CC value set to 833.

That said, you should take a look at the project attached in this post. It uses the SAADC to implement a UART RX and PWM for UART TX.

Alternatively, you could upgrade to nRF52840 to get 2 UART(E) peripherals.