"Event endpoints are only able to recognize addresses from the EVENT group" Can you please explain it properly?

RE: "Event endpoints are only able to recognize addresses from the EVENT group" Can you please explain it properly?

Håkon Alseth — Wed, 25 Jun 2014 09:04:45 GMT

This is a function that handles configuration of PPI channels when the softdevice is enabled and disabled. Since the softdevice uses the PPI, it is a restricted peripheral and should be accessed via the nrf_soc library when it's enabled.

You can call this function similar to this: "ppi_enable_channel(MY_PPI_CHANNEL, &NRF_TIMER0->EVENTS_COMPARE[0], &NRF_ADC->TASKS_START);"

RE: "Event endpoints are only able to recognize addresses from the EVENT group" Can you please explain it properly?

krishna — Tue, 24 Jun 2014 13:37:28 GMT

Thank you very much for your answer. But in this below code what will be *event_ptr and *task_ptr?

void ppi_enable_channel(uint32_t ch_num, volatile uint32_t *event_ptr, volatile uint32_t *task_ptr)
{
    if(ch_num >= 16)
    {
        return;
    }
    else
    {
#if(USE_WITH_SOFTDEVICE == 1)
        sd_ppi_channel_assign(ch_num, event_ptr, task_ptr);
        sd_ppi_channel_enable_set(1 << ch_num);
#else
        // Otherwise we configure the channel and return the channel number
        NRF_PPI->CH[ch_num].EEP = (uint32_t)event_ptr;
        NRF_PPI->CH[ch_num].TEP = (uint32_t)task_ptr;
        NRF_PPI->CHENSET = (1 << ch_num);
#endif

moderator edit: use of code tags

RE: "Event endpoints are only able to recognize addresses from the EVENT group" Can you please explain it properly?

Håkon Alseth — Tue, 24 Jun 2014 13:32:24 GMT

Since you've quoted from the PPI chapter in the reference manual, you're asking about how the PPI event endpoints (NRF_PPI->CH[x].EEP) and task endpoints (NRF_PPI->CH[x].TEP) works. The Programmable Peripheral Interconnect (short: PPI) is a peripheral that takes in a event and then starts a task, without involving the MCU (other than the initial configuration)

A PPI event endpoint register must hold the address of an valid event given by the nRF51x22. This can be any event generated by any of the peripherals. For instance:

NRF_PPI->CH[0].EEP = (uint32_t)&NRF_TIMER0->EVENTS_COMPARE[0];

In order for the above event (in this case, timer0's compare[0]) to actually have an effect through the PPI, you must also configure the Task End Point (TEP). The address that you give into the TEP must be a valid TASKS_* address, for instance:

NRF_PPI->CH[0].TEP = (uint32_t)&NRF_ADC->TASKS_START;

Now, given that the two peripherals that you've connected through the PPI are configured correctly, and the specific PPI channel is enabled (NRF_PPI->CHENSET = PPI_CHENSET_CH0_Enabled << PPI_CHENSET_CH0_Pos;), the ADC will do a conversion each time the NRF_TIMER->EVENTS_COMPARE[0] occurs.

I would recommend that you look at the PPI-example in the SDK, as well as the gpiote_example, as it also uses the PPI. If you look at this example on github, which will create a 8 MHz pulse on a GPIO, it also uses the PPI to make this happen: github.com/.../main.c