Fast Ethernet Controller (FEC)
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
45-27
Table 45-24
describes R
—
FSTART fields.
45.3.2.17 Transmit Watermark Register (X_WMRK)
The X_WMRK register, shown in
Figure 45-21
, is used to control the amount of data required in the
transmit FIFO before transmission of a frame can begin. This allows the user to minimize transmit latency
(X_WMRK = 0x) or allow larger bus access latency (X_WMRK = 11) due to contention for the system
bus. Setting the watermark to a high value lowers the risk of a transmit FIFO underrun due to system bus
contention.
0
15
Field
—
Reset
0000_0000_0000_0000
R/W
R/W
Addr
0x0ED0 (FEC1) & 0x1ED0 (FEC2)
16
20
21
22
29
30
31
Field
—
1
R_FSTART
—
Reset
0000_0000_0000_0000
R/W
R/W
Addr
0x0ED2 (FEC1) & 0x1ED2 (FEC2)
Figure 45-20. R_FSTART Register
Table 45-24. R_FSTART Field Descriptions
Bits
Name
Description
0–21
—
Reserved. Note all bits read back as 0 except for 21, which returns a 1.
22–29
R_FSTART
Address of first receive FIFO location. Acts as a delimiter between receive and transmit FIFOs.
30–31
—
Reserved, should be cleared by the host processor.
0
15
Field
—
Reset
0000_0000_0000_0000
R/W
R/W
Addr
0x0EE4 (FEC1) & 0x1EE4 (FEC2)
16
29
30
31
Field
—
X_WMRK
Reset
0000_0000_0000_0000
R/W
R/W
Addr
0x0EE6 (FEC1) & 0x1EE6 (FEC2)
Figure 45-21. X_WMRK Register
Summary of Contents for PowerQUICC MPC870
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Page 1312: ...Byte Ordering MPC885 PowerQUICC Family Reference Manual Rev 2 A 8 Freescale Semiconductor ...
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Page 1370: ...MPC880 MPC885 PowerQUICC Family Reference Manual Rev 2 E 4 Freescale Semiconductor ...
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