11-38
MCF5272 User’s Manual
Differences between MCF5272 FEC and MPC860T FEC
An underrun occurs when, during transmit, the transmit FIFO empties before the end of the
frame. Then, a bad CRC is appended to the partially transmitted data. In addition, the UN
bit is set in the last BD for the current frame. This situation can occur if the FEC cannot
access an internal bus, or if the next BD in the frame is not available.
NOTE:
Anytime the software driver sets an R bit in a transmit
descriptor, the driver should immediately write to
X_DES_ACTIVE.
11.7 Differences between MCF5272 FEC and
MPC860T FEC
The MCF5272 features the same FEC as the MPC860T with a few differences. The
following list pertains to the MCF5272.
•
Limited throughput full-duplex 100 Mbps operation. External bus use is the limiting
factor.
•
Only big-endian mode is supported for buffer descriptors and buffers.
•
Separate interrupt vectors for Rx, Tx and non-time critical interrupts
•
Interrupt priority is set in the interrupt controller
•
The formula for calculating E_MDC clock frequency differs between MCF5272 and
MPC860T:
— MCF5272: E_MDC_FREQUENCY= system frequency / (4 * MII_SPEED)
— MPC860T: E_MDC_FREQUENCY= system frequency / (2 * MII_SPEED)
NOTE:
MCF5272 ethernet controller signal names are generally
identical to those used in the MPC860T, except for a prefix of
‘E_’. For example, MDC in the MPC860T corresponds to
E_MDC in the MCF5272.
-
Data Length
Written by the user. Data length is the number of octets the FEC should transmit
from this BD’s data buffer. It is never modified by the FEC. Bits [10–0] are used
by the DMA engine; bits [15–11] are ignored.
-
Tx Buffer Pointer Written by the user. The transmit buffer pointer, which contains the address of the
associated data buffer, may be even or odd. The buffer must reside in memory
external to the FEC. This value is never modified by the FEC.
Table 11-35. TxBD Field Descriptions (Continued)
Bits
Name
Description
Summary of Contents for DigitalDNA ColdFire MCF5272
Page 1: ...MCF5272UM D Rev 0 02 2001 MCF5272 ColdFire Integrated Microprocessor User s Manual ...
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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 ...