DPPI — Distributed programmable peripheral interconnect

The DPPI system directs peripheral events to a channel (publishing) and converts events from a channel into peripheral tasks (subscribing).

All peripherals include the following:

• One publish register per event
• One subscribe register per task

The publish and subscribe registers have two fields. A channel index field (CHIDX) determines which channel an event is published to, or which channel a task is subscribed to. In addition there is an ENABLE field that must be set to 1 to activate the operation.

Writing non-existing channel index (CHIDX) numbers into a peripheral's publish or subscribe registers will yield unexpected results.

One event can trigger multiple tasks by subscribing different tasks to the same channel. Similarly, one task can be triggered by multiple events by publishing different events to the same channel. For advanced use cases, multiple events and multiple tasks can connect to the same channel forming a many-to-many connection. If multiple events are published on the same channel at the same time, the events are merged and only one event is routed through the DPPI.

The following figure shows how peripheral events are routed onto different channels based on publish registers.

The following figure illustrates how peripheral tasks are triggered from different channels based on subscribe registers.

Enabling and disabling of DPPI channels is handled through DPPIC.

There are two ways of enabling or disabling a DPPI channel using DPPIC:

• Enable or disable channels individually using registers CHEN, CHENSET, and CHENCLR.
• Enable or disable channels in channel groups using the groups' tasks ENABLE and DISABLE. Channel groups should be defined via the CHG registers before these tasks are triggered.

DPPIC tasks (for example CHG[0].EN) can be triggered through DPPI like any other task, which means they can be linked to a DPPI channel through the subscribe registers.

In order to write to CHG[n], the corresponding CHG[n].EN and CHG[n].DIS subscribe registers must be disabled. Writes to CHG[n] are ignored if any of the two subscribe registers are enabled.

Several connection options are available with DPPI. Examples are given for how to create one-to-one and many-to-many connections.

NRF_TIMER20->PUBLISH_COMPARE[0] = (0 << TIMER_PUBLISH_COMPARE_CHIDX_Pos) | TIMER_PUBLISH_COMPARE_EN_Msk;
NRF_SAADC->SUBSCRIBE_START = (0 << SAADC_SUBSCRIBE_START_CHIDX_Pos) | SAADC_SUBSCRIBE_START_EN_Msk;
NRF_DPPIC20->CHENSET = DPPIC_CHENSET_CH0_Msk;
            

NRF_DPPIC20->CHG[0] = (DPPIC_CHG_CH0_Included << DPPIC_CHG_CH0_Pos);
NRF_GPIOTE20->PUBLISH_IN[0] = (0 << GPIOTE_PUBLISH_IN_CHIDX_Pos) | GPIOTE_PUBLISH_IN_EN_Msk;
NRF_TIMER20->PUBLISH_COMPARE[0] = (0 << TIMER_PUBLISH_COMPARE_CHIDX_Pos) | TIMER_PUBLISH_COMPARE_EN_Msk;
NRF_SAADC->SUBSCRIBE_START = (0 << SAADC_SUBSCRIBE_START_CHIDX_Pos) | SAADC_SUBSCRIBE_START_EN_Msk;
NRF_DPPIC20->SUBSCRIBE_CHG[0].DIS = DPPIC_CHENSET_CH0_Msk | DPPIC_SUBSCRIBE_CHG_DIS_EN_Msk;
NRF_DPPIC20->TASK_CHG[0].EN = 1;