Sundance SMT335E - Manual (Page 25)

Version 1.5 Page 25 of 53 SMT335E SMT375E User Manual
DMA
SDB transfers can be performed using DMA without any processor interaction.
The DMA should be set to transfer frames of up to 255 words, with read
synchronisation on the SDB’s interrupt condition. The FIFO must be addressed using
consecutive word addresses to allow for correct synchronisation; you must not use
an increment of zero on the DMA’s address into the FIFO. For transfers of more than
one frame, you must use a global index register to adjust the DMA’s address into the
FIFO as follows (note the negative frame index):
SDB OTRIGGER = FRAMESIZE
SDB ITRIGGER = FRAMESIZE
DMA Global Index = (Frame Index<<16) + Element Index
Element Index = 4
where
Frame Index = – 4*(FRAMESIZE-1)
The transfer will access words at offsets in the FIFO from 0 to FRAMESIZE-1.
Applying the negative Frame Index at the end of the frame will bring the offset back
to 0. Accessing the word at offset FRAMESIZE-1 will allow synchronisation by a new
interrupt condition.
The SDB interrupt condition must be mapped in one of the interrupt control registers
to provide synchronisation on one of the external interrupt lines. The first
synchronisation event will be generated when the interrupt control register has been
written and the condition becomes true.
Examples of DMA transfers are provided on the distribution disk.