13.14.5.3 Clocks
The DMAC bus clock (CLK_DMAC_APB) must be configured and enabled in the Main Clock module before using the DMAC.
This bus clock (CLK_DMAC_APB) is always synchronous to the module clock (CLK_DMAC_AHB), but can be divided by a prescaler and may run even when the module clock is turned off.