The DMA will always use SINGLE, or INCR type AHB accesses for buffer management operations. When performing data transfers, the AHB burst length is selected by the Fixed Burst Length for DMA Data Operations bit field in the DMA Configuration register (GMAC_DCFGR.FBLDO) so that either SINGLEor fixed length incrementing bursts (INCR4, INCR8 or INCR16) are used where possible:
When there is enough space and enough data to be transferred, the programmed fixed length bursts will be used. If there is not enough data or space available, for example when at the beginning or the end of a buffer, SINGLE type accesses are used. Also SINGLE type accesses are used at 1024 Byte boundaries, so that the 1 KByte boundaries are not burst over as per AHB requirements.
The DMA will not terminate a fixed length burst early, unless an error condition occurs on the AHB or if receive or transmit are disabled in the Network Control register (GMAC_NCR).