Can anybody please explain the blinky program in nrf51 examples?

RE: Can anybody please explain the blinky program in nrf51 examples?

Stian Røed Hafskjold — Mon, 23 May 2016 14:25:41 GMT

Please click the accept button if you find any of the answers useful.

RE: Can anybody please explain the blinky program in nrf51 examples?

Sara — Tue, 17 May 2016 11:40:45 GMT

thank you so much for the answers.

RE: Can anybody please explain the blinky program in nrf51 examples?

Stian Røed Hafskjold — Sun, 15 May 2016 19:30:47 GMT

A '1' in the 32-bit number you pass to NRF_GPIO->OUTSET will set the corresponding bit in the NRF_GPIO->OUT register, a '0' will have no effect. Similarly, a '1' in the OUTCLR register will clear the bit, '0' will have no effect.

Let's say you want to toggle NRF_GPIO->OUT[0] and NRF_GPIO->OUT[2], and [0] is '1' and [2] is '0' (using only 4 bits to keep it simple):

NRF_GPIO->OUT: 0b0001 // initial state of the register

LEDS_INVERT(0b0101);  // pass the mask of the LEDs you want to invert

LEDS_INVERT() does this:

uint32_t gpio_state = NRF_GPIO->OUT;  // Reads the state of NRF_GPIO->OUT
                                      // It gets the value 0b0001

NRF_GPIO->OUTSET = ((leds_mask) & ~gpio_state);  // 0b0101 & ~0b0001
                                                 // = 0b0101 & 0b1110 = 0b0100
                                                 // It sets NRF_GPIO->OUT[2] to 1 leaving the other bits

NRF_GPIO->OUTCLR = ((leds_mask) & gpio_state);   // 0b0101 & 0b0001 = 0b0001
                                                 // It clears NRF_GPIO->OUT[0] to 0 leaving the other bits

NRF_GPIO->OUT: 0b0100 // resulting state of the register

And the reason why this is put in a do {...} while(0) statement, you can read about here: stackoverflow.com/.../257425

RE: Can anybody please explain the blinky program in nrf51 examples?

itssead — Sun, 15 May 2016 19:26:56 GMT

(see other detailed answer - dup) here is a nice explanation of this "strange" looking "do {} while (0)" define

Answer 5: stackoverflow.com/.../do-while-0-what-is-it-good-for

"It's the only construct in C that you can use to #define a multistatement operation, put a semicolon after, and still use within an if statement." Greg Hewgill

RE: Can anybody please explain the blinky program in nrf51 examples?

Christopher — Sun, 15 May 2016 15:59:54 GMT

This is another way to toggle a GPIO:

/**
 * @brief Toggle GPIO pin.
 *
 * Note that the pin must be configured as an output for this function to have any effect.
 *
 * @param pin_number specifies the pin number [0:31] to toggle.
 */
static __INLINE void nrf_gpio_pin_toggle(uint32_t pin_number)
{
    NRF_GPIO->OUT ^= (1UL << pin_number);
}

Please have a look at the GPIO abstraction documentation here: infocenter.nordicsemi.com/index.jsp