11-16
MCF5272 User’s Manual
Programming Model
Figure 11-8. R_DES_ACTIVE Register
11.5.6 Transmit Descriptor Active Register
(X_DES_ACTIVE)
The X_DES_ACTIVE 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 X_DES_ACTIVE 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 X_DES_ACTIVE register is cleared at reset and when ETHER_EN is cleared.
Figure 11-9 describes this register.
31
25
24
23
16
Field
—
R_DES_ACTIVE
—
Reset
0000_0000_0000_0000
R/W
Read/Write
15
0
Field
—
Reset
0000_0000_0000_0000
R/W
Read/Write
Addr
MBAR + 0x850
Table 11-11. describes the R_DES_ACTIVE fields.
Table 11-11. R_DES_ACTIVE Register Field Descriptions
Bit
Name
Description
31–25
—
Reserved, should be cleared.
24
R_DES_ACTIVE
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.
23–0
—
Reserved, should be cleared.
Summary of Contents for DigitalDNA ColdFire MCF5272
Page 1: ...MCF5272UM D Rev 0 02 2001 MCF5272 ColdFire Integrated Microprocessor User s Manual ...
Page 38: ...xxxviii MCF5272 User s Manual TABLES Table Number Title Page Number ...
Page 58: ...1 10 MCF5272 User s Manual MCF5272 Specific Features ...
Page 90: ...2 42 MCF5272 User s Manual Exception Processing Overview ...
Page 96: ...3 6 MCF5272 User s Manual MAC Instruction Execution Timings ...
Page 158: ...5 46 MCF5272 User s Manual Motorola Recommended BDM Pinout ...
Page 184: ...7 12 MCF5272 User s Manual Interrupt Controller Registers ...
Page 338: ...13 44 MCF5272 User s Manual Application Examples ...
Page 414: ...18 6 MCF5272 User s Manual PWM Programming Model ...
Page 452: ...19 38 MCF5272 User s Manual Power Supply Pins ...
Page 482: ...20 30 MCF5272 User s Manual Reset Operation ...
Page 492: ...21 10 MCF5272 User s Manual Non IEEE 1149 1 Operation ...