35.6.4.1 DMA Operation

The TCC can generate the following DMA requests:

Counter overflow (OVF)

If the One-shot Trigger mode in the control A register (CTRLA.DMAOS) is written to '0', the TCC generates a DMA request on each cycle when an update condition (Overflow, Underflow or Re-trigger) is detected.

When an update condition (Overflow, Underflow or Re-trigger) is detected while CTRLA.DMAOS = 1, the TCC generates a DMA trigger on the cycle following the DMA One-Shot Command written to the Control B register (CTRLBSET.CMD = DMAOS).

In both cases, the request is cleared by hardware on DMA acknowledge.

Note: Counter Overflow (OVF) DMA Trigger in DMA One-Shot Trigger Mode (CTRLA.DMAOS = 1) is not functional for Critical RAMP2C and RAMP2CS operation modes.

Channel Match (MCx)

A DMA request is set only on a compare match if CTRLA.DMAOS = 0. The request is cleared by hardware on DMA acknowledge.

When CTRLA.DMAOS = 1, the DMA requests are not generated.

Channel Capture (MCx)

For a capture channel, the request is set when valid data is present in the CCx register, and cleared once the CCx register is read.

In this operation mode, the CTRLA.DMAOS bit value is ignored.

DMA Operation with Circular Buffer

When circular buffer operation is enabled, the Buffer registers must be written in a correct order and synchronized to the update times of the timer. The DMA triggers of the TCC provide a way to ensure a safe and correct update of circular buffers.

Note: Circular buffer are intended to be used with RAMP2, RAMP2A and DSBOTH operation only.

DMA Operation with Circular Buffer in RAMP2 and RAMP2A Mode

When a CCx channel is selected as a circular buffer, the related DMA request is not set on a compare match detection, but on start of ramp B.

If at least one circular buffer is enabled, the DMA overflow request is conditioned to the start of ramp A with an effective DMA transfer on previous ramp B (DMA acknowledge).

The update of all circular buffer values for ramp A can be done through a DMA channel triggered on a MC trigger. The update of all circular buffer values for ramp B, can be done through a second DMA channel triggered by the overflow DMA request.

Figure 35-40. DMA Triggers in RAMP and RAMP2 Operation Mode and Circular Buffer Enabled

DMA Operation with Circular Buffer in DSBOTH Mode

When a CC channel is selected as a circular buffer, the related DMA request is not set on a compare match detection, but on start of down-counting phase.

If at least one circular buffer is enabled, the DMA overflow request is conditioned to the start of up-counting phase with an effective DMA transfer on previous down-counting phase (DMA acknowledge).

When up-counting, all circular buffer values can be updated through a DMA channel triggered by MC trigger. When down-counting, all circular buffer values can be updated through a second DMA channel, triggered by the OVF DMA request.

Figure 35-41. DMA Triggers in DSBOTH Operation Mode and Circular Buffer Enabled