NUC970 Technical Reference Manual
Publication Release Date: Dec. 15, 2015
- 623 -
Revision V1.30
NUC97
0
T
E
CHNIC
A
L
RE
F
E
RE
N
CE
MA
NUA
L
[9:8]
TXTHD
TXFIFO Low Threshold
The TXTHD 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.
00 = Undefined.
10 = TXFIFO low threshold is 80B and high threshold is 160B.
01 = TXFIFO low threshold is 64B and high threshold is 128B.
11 = TXFIFO low threshold is 96B and high threshold is 192B.
[7:2]
Reserved
Reserved.
[1:0]
RXTHD
RXFIFO Low Threshold
The RXTHD 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.
00 = Depend on the burst length setting. If the burst length is 8 words, high threshold is 8
words, too.
01 = RXFIFO high threshold is 64B and low threshold is 32B.
10 = RXFIFO high threshold is 128B and low threshold is 64B.
11 = RXFIFO high threshold is 192B and low threshold is 96B.