Sundance Spas ST201 - Manual (Page 77)

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Sundance Technology ST201 PRELIMINARY draft 2
RXDMAURGENTTHRESH
Class....................I/O Registers, DMA
Base Address ......IoBaseAddress register value
Address Offset .....0x15
Access Mode .......Read/Write
Width ...................8 bits
The value in RxDMAUrgentThresh sets a threshold at which the RxDMA engine will make a urgent bus
master request. A urgent RxDMA request will have priority over all other requests on the ST201. The
urgent bus request is made when the free space in the RxFIFO falls below the value in RxDMAUrgent-
Thresh. A RxDMA urgent request is not subject to the RxDMABurstThresh constraint. When the RxFIFO is
close to overrun, burst efficiency is sacrificed in favor of requesting the bus as quickly as possible. The
value in RxDMAUrgentThresh represents free space in the RxFIFO in terms of 32-byte portions. RxDMAU-
rgentThresh resets to 4, or a threshold of 128 bytes.
BIT BIT NAME BIT DESCRIPTION
4..0 RxDMAUrgent-
Thresh The minimum number of 32-byte words which must be available in the
RxFIFO to avoid assertion of a RxDMA Urgent Request.
7..5 Unused These bits are ignored.