Fast Ethernet Controller (FEC)
MPC885 PowerQUICC Family Reference Manual, Rev. 2
45-22
Freescale Semiconductor
Table 45-18
describes R_DES_ACTIVE fields.
45.3.2.12 TxBD Active Register (X_DES_ACTIVE)
The TxBD active register, shown in
Figure 45-16
, is a command register that the user should write to
indicate that the TxBD ring was updated (transmit buffers have been produced by the software driver with
TxBD[R] set).
Whenever the register is written, X_DES_ACTIVE is set, regardless of the data written by the user. When
the bit is set, the TxBD ring is polled and transmit frames (provided ECNTRL[ETHER_EN] is also set)
are processed. Once a TxBD whose R bit is not set is polled, X_DES_ACTIVE is cleared and polling stops
until the bit is set, signifying additional BDs have been placed into the TxBD ring.
X_DES_ACTIVE is cleared at reset and by clearing ECNTRL[ETHER_EN].
45.3.2.13 MII Management Frame Register (MII_DATA)
Table 45-19
describes X_DES_ACTIVE fields.
Table 45-18. R_DES_ACTIVE Field Descriptions
Bits
Name
Description
0–6
—
Reserved
7
R_DES_ACTIVE
Signals the FEC that empty buffers are available. Set when this register is written,
regardless of the value written. Cleared by the FEC whenever no additional BDs are ready
in the RxBD ring.
8–31
—
Reserved
0
6
7
8
15
Field
—
X_DES_ACTIVE
—
Reset
0000_0000_0000_0000
R/W
R/W
Addr
0x0E54 (FEC1) & 0x1E54 (FEC2)
16
31
Field
—
Reset
0000_0000_0000_0000
R/W
R/W
Addr
0x0E56 (FEC1) & 0x1E56 (FEC2)
Figure 45-16. X_DES_ACTIVE Register
Summary of Contents for PowerQUICC MPC870
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