ST STM32G0 1 Series Reference Manual page 283

RM0444
register content may not correctly reflect the remaining data transfers versus the
aborted source and destination buffer/register.
•
Abort and restart a channel
This corresponds to the software sequence: disable an active channel, then
reconfigure the channel and enable it again.
This is supported by the hardware if the following conditions are met:
–
–
When a channel transfer error occurs, the EN bit of the DMA_CCRx register is cleared by
hardware. This EN bit can not be set again by software to re-activate the channel x, until the
TEIFx bit of the DMA_ISR register is set.
Circular mode (in memory-to-peripheral/peripheral-to-memory transfers)
The circular mode is available to handle circular buffers and continuous data flows (such as
ADC scan mode). This feature is enabled using the CIRC bit in the DMA_CCRx register.
Note: The circular mode must not be used in memory-to-memory mode. Before enabling a
channel in circular mode (CIRC = 1), the software must clear the MEM2MEM bit of the
DMA_CCRx register. When the circular mode is activated, the amount of data to transfer is
automatically reloaded with the initial value programmed during the channel configuration
phase, and the DMA requests continue to be served.
In order to stop a circular transfer, the software needs to stop the peripheral from generating
DMA requests (such as quit the ADC scan mode), before disabling the DMA channel.
The software must explicitly program the DMA_CNDTRx value before starting/enabling a
transfer, and after having stopped a circular transfer.
Memory-to-memory mode
The DMA channels may operate without being triggered by a request from a peripheral. This
mode is called memory-to-memory mode, and is initiated by software.
If the MEM2MEM bit in the DMA_CCRx register is set, the channel, if enabled, initiates
transfers. The transfer stops once the DMA_CNDTRx register reaches zero.
Note: The memory-to-memory mode must not be used in circular mode. Before enabling a
channel in memory-to-memory mode (MEM2MEM = 1), the software must clear the CIRC
bit of the DMA_CCRx register.
The application guarantees that, when the software is disabling the channel, a
DMA data transfer is not occurring at the same time over its master port. For
example, the application can first disable the peripheral in DMA mode, in order to
ensure that there is no pending hardware DMA request from this peripheral.
The software must operate separated write accesses to the same DMA_CCRx
register: First disable the channel. Second reconfigure the channel for a next block
transfer including the DMA_CCRx if a configuration change is needed. There are
read-only DMA_CCRx register fields when DMA_CCRx.EN=1. Finally enable
again the channel.
Direct memory access controller (DMA)
RM0444 Rev 5 283/1390
297