Sundance Spas ST201 - Manual (Page 81)

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Sundance Technology ST201 PRELIMINARY draft 2
TXDMAURGENTTHRESH
Class....................I/O Registers, DMA
Base Address ......IoBaseAddress register value
Address Offset .....0x09
Access Mode .......Read/Write
Width ...................8 bits
When the number of used bytes in the TxFIFO falls below the value in the TxDMAUrgentThresh, the
TxDMA Logic will make an urgent bus master request. An urgent TxDMA request will have priority over the
RxDMA, unless it is also making an urgent request. A TxDMA urgent request is not subject to the
TxDMABurstThresh constraint. The relaxation of the TxDMABurstThresh constraint for this condition is
because the TxFIFO is close to under run, and burst efficiency is sacrificed to avoid FIFO under run. The
value in TxDMAUrgentThresh represents data in the TxFIFO in multiples of 32 bytes. TxDMAUrgent-
Thresh resets to 4, or a threshold of 128 bytes.
BIT BIT NAME BIT DESCRIPTION
5..0 TxDMAUrgent-
Thresh The minimum number of 32-byte words which must be occupied in the
TxFIFO to avoid assertion of a TxDMA Urgent Request.
7..6 Unused These bits are ignored.