MCF5272CVM66 Datasheet, PDF (250/544 Pages) Freescale Semiconductor, Inc – MCF5272 ColdFire® Integrated Microprocessor

Ethernet Module
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 11-26, is not reset and must be initialized by the user prior to operation.
31
Field
Reset
R/W
—
0000_0000_0000_0000
Read/Write
15
Field
Reset
R/W
Addr
11
10
—
R_BUFF_SIZE
4
3
0000_0
Read/Write
MBAR + 0xC18
Figure 11-26. Receive Buffer Size (EMRBR)
Table 11-29. EMRBR Field Descriptions
Bits
31–11
10–4
3–0
Name
—
R_BUFF_SIZE
—
Reserved, should be cleared.
Receive buffer size.
Reserved, should be cleared.
Description
16
0
—
0000
11-32
MCF5272 ColdFire^® Integrated Microprocessor User’s Manual, Rev. 3
Freescale Semiconductor