mcf5272 Freescale Semiconductor, Inc, mcf5272 Datasheet - Page 253

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

MOTOROLA
11.5.21 Receive Buffer Size Register (EMRBR)
The EMRBR register dictates the maximum size of all receive buffers. Note that because
receive frames are truncated at 2k-1 bytes, only bits 10–4 are used. This value should take
into consideration that the receive CRC is always written into the last receive buffer. To
allow one maximum size frame per buffer, R_BUFF_SIZE must be set to MAX_FL or
larger. The R_BUFF_SIZE must be evenly divisible by 16. To insure this, bits 3–0 are
forced low. To minimize bus utilization (descriptor fetches), it is recommended that
R_BUFF_SIZE be at least 256 bytes.
This register, Figure 11-25, is not reset and must be initialized by the user prior to
operation.
Reset
Reset
Reset
Reset
Field
Field
Addr
Field
Field
Addr
R/W
R/W
R/W
R/W
31–2
31
15
31
15
Bits
1–0
Figure 11-24. Pointer to Transmit Descriptor Ring (ETDSR)
X_DES_START
0000_0
—
Name
—
Figure 11-25. Receive Buffer Size (EMRBR)
Table 11-28. ETDSR Field Descriptions
11
Pointer to start of transmit buffer descriptor queue.
Reserved, should be cleared.
Chapter 11. Ethernet Module
10
X_DES_START
0000_0000_0000_0000
X_DES_START
MBAR + 0xC14
MBAR + 0xC18
Read/Write
Read/Write
Read/Write
Read/Write
Undefined
Undefined
R_BUFF_SIZE
—
Description
4
3
Programming Model
2
0000
—
1
0
11-29
16
16
0
0
0