Cirrus Logic EP93xx - Manual (Page 392)

9-90 DS785UM1
Copyright 2007 Cirrus Logic
1/10/100 Mbps Ethernet LAN Controller
EP93xx User’s Guide
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RDST: Receive Descriptor Soft Threshold.
The hard and soft threshold work in exactly the same
manner except one. The soft threshold will not cause a
bus request to be made if the bus is currently in use, but
only when it is deemed to be idle (no transfers for four
AHB clocks). The hard threshold takes effect immediately
regardless of the state of the bus. This operation allows for
more efficient use of the AHB bus by allowing smaller
transfers to take place when the bus is lightly loaded and
requesting larger transfers only when the bus is more
heavily loaded.
TXDThrshld
Address:
0x8001_00E4 - Read/Write
Suggested Value:
0x0004_0002
Chip Reset:
0x0000_0000
Soft Reset:
Unchanged
Definition:
Transmit Descriptor Threshold register. The transmit descriptor thresholds are
used to set a limit on the amount of empty space allowed in the MAC’s
transmit descriptor FIFO before a bus request will be scheduled. When the
number of empty words in the FIFO exceeds the threshold value, the
Descriptor Processor will schedule a bus request to transfer descriptors. The
actual posting of the bus request may be delayed due to lack of resources in
the MAC, such as a TXDEnq equal to zero. The lower two bits of the
thresholds are always zero.
Bit Descriptions:
RSVD: Reserved. Unknown During Read.
0: Must be written as “0”.
TDHT: Transmit Descriptor Hard Threshold.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
RSVD TDHT 0 0
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
RSVD TDST 0 0