mcf5272 Freescale Semiconductor, Inc, mcf5272 Datasheet - Page 240

• Manufacturer Part Number: mcf5272
• Description: Mcf5272 Coldfire Integrated Microprocessor User
• Manufacturer: Freescale Semiconductor, Inc

Programming Model
Table 11-11 describes the RDAR fields.
11.5.6 Transmit Descriptor Active Register (TDAR)
The TDAR register, Figure 11-9, is a command register which should be set by the user to
indicate that the transmit descriptor ring has been updated, that is, transmit buffers have
been defined by the driver with the ready bit set in the buffer descriptor.
The X_DES_ACTIVE bit is set whenever the register is written. This is independent of the
data actually written by the user. When TDAR is set, the FEC polls the transmit descriptor
ring and processes transmit frames (provided ETHER_EN is also set). As soon as the FEC
polls a transmit descriptor whose ready bit is not set, it clears the X_DES_ACTIVE bit and
stops polling the transmit descriptor ring.
The TDAR register is cleared at reset and when ETHER_EN is cleared. Figure 11-9
describes this register.
Table 11-12 describes the TDAR fields.
11-16
31–25
23–0
Bit
24
31–25
23–0
Bits
Reset
Reset
24
Field
Field
Addr
R/W
R/W
R_DES_ACTIVE
31
15
X_DES_ACTIVE Set to one when this register is written, regardless of the value written. Cleared by
Name
—
—
Name
—
—
Table 11-11. RDAR Register Field Descriptions
—
Reserved, should be cleared.
Set when this register is written, regardless of the value written. Cleared by the FEC
whenever no additional empty descriptors remain in the receive ring.
Reserved, should be cleared.
Reserved, should be cleared.
the FEC whenever no additional ready descriptors remain in the transmit ring.
Reserved, should be cleared.
Table 11-12. TDAR Field Descriptions
Figure 11-9. TDAR Register
MCF5272 User’s Manual
25
X_DES_ACTIVE
0000_0000_0000_0000
0000_0000_0000_0000
MBAR +0x854
Read/Write
Read/Write
24
—
Description
Description
23
—
MOTOROLA
16
0