Freescale Semiconductor MPC5200B ユーザーズマニュアル
FEC Registers—MBAR + 0x3000
MPC5200B Users Guide, Rev. 1
Freescale Semiconductor
14-15
The R_DES_ACTIVE bit is cleared at reset and by the clearing of ETHER_EN.
14.5.5
FEC Tx Descriptor Active Register—MBAR + 0x3014
The FEC descriptor active register is a command register which should be written by the user to indicate that the transmit descriptor ring has
been updated (transmit buffers have been produced by the driver with the R bit set in the buffer descriptor).
been updated (transmit buffers have been produced by the driver with the R bit set in the buffer descriptor).
Whenever the register is written the X_DES_ACTIVE bit is set. This is independent of the data actually written by the user. When set, the
FEC will poll the transmit descriptor ring and process transmit frames (provided ETHER_EN is also set). Once the FEC polls a transmit
descriptor whose ownership bit is not set, then the FEC will clear the X_DES_ACTIVE bit and cease transmit descriptor ring polling until the
sets the bit again, signifying additional descriptors have been placed into the transmit descriptor ring.
FEC will poll the transmit descriptor ring and process transmit frames (provided ETHER_EN is also set). Once the FEC polls a transmit
descriptor whose ownership bit is not set, then the FEC will clear the X_DES_ACTIVE bit and cease transmit descriptor ring polling until the
sets the bit again, signifying additional descriptors have been placed into the transmit descriptor ring.
The X_DES_ACTIVE bit is cleared at reset and by the clearing of ETHER_EN.
Table 14-12. FEC Rx Descriptor Active Register
msb 0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
R
Reserved
R
_
DES_A
C
TIVE
Reserved
W
RESET:
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31 lsb
R
Reserved
W
RESET:
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Bits
Name
Description
0:6
—
Reserved
7
R_DES_ACTIVE Set to one when this register is written, regardless of the value written. Cleared by the
FEC device whenever no additional “ready” descriptors remain in the receive ring.
8:31
—
Reserved
Table 14-13. FEC Tx Descriptor Active Register
msb 0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
R
Reserved
X_D
E
S_A
C
TIVE
Reserved
W
RESET:
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31 lsb
R
Reserved
W
RESET:
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0