Rainbow Electronics W90N745CDG - Manual (Page 132)

W90N745CD/W90N745CDG
Publication Release Date: September 22, 2006
- 127 - Revision A2
Continued.
BITS DESCRIPTIONS
[9:8] TxTHD
The TxFIFO Low Threshold controls when TxDMA requests internal
arbiter for data transfer between system memory and TxFIFO. The
TxTHD defines not only the low threshold of TxFIFO, but also the high
threshold. The high threshold is the twice of low threshold always.
During the packet transmission, if the TxFIFO reaches the high
threshold, the TxDMA stops generate request to transfer frame data
from system memory to TxFIFO. If the frame data in TxFIFO is less
than low threshold, TxDMA starts to transfer frame data from system
memory to TxFIFO.
The TxTHD also defines when the TxMAC starts to transmit frame out
to network. The TxMAC starts to transmit the frame out while the
TxFIFO first time reaches the high threshold during the transmission
of the frame. If the frame data length is less than TxFIFO high
threshold, the TxMAC starts to transmit the frame out after the frame
data are all inside the TxFIFO.
2’b00: Undefined.
2’b01: TxFIFO low threshold is 64B and high threshold is 128B.
2’b10: TxFIFO low threshold is 80B and high threshold is 160B.
2’b11: TxFIFO low threshold is 96B and high threshold is 192B.
[7:2] Reserved
[1:0] RxTHD
The RxFIFO High Threshold controls when RxDMA requests internal
arbiter for data transfer between RxFIFO and system memory. The
RxTHD defines not only the high threshold of RxFIFO, but also the low
threshold. The low threshold is the half of high threshold always.
During the packet reception, if the RxFIFO reaches the high threshold,
the RxDMA starts to transfer frame data from RxFIFO to system
memory. If the frame data in RxFIFO is less than low threshold,
RxDMA stops to transfer the frame data to system memory.
2’b00: Depend on the burst length setting. If the burst length is 8
words, high threshold is 8 words, too.
2’b01: RxFIFO high threshold is 64B and low threshold is 32B.
2’b10: RxFIFO high threshold is 128B and low threshold is 64B.
2’b11: RxFIFO high threshold is 192B and low threshold is 96B.