Receive Buffer Size Register (R_Buff_Size) - Motorola DigitalDNA ColdFire MCF5272 User Manual

Programming Model
Table 11-28. X_DES_START Field Descriptions
Bits Name
31–2 X_DES_START
1–0

11.5.21 Receive Buffer Size Register (R_BUFF_SIZE)

The R_BUFF_SIZE registers 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.
31
Field
Reset
R/W
15
Field —
Reset 0000_0
R/W
Addr
Figure 11-25. Receive Buffer Size (R_BUFF_SIZE)
Bits
31–11
10–4
3–0
11.5.22 Initialization Sequence
This section describes which registers and RAM locations are reset due to hardware reset,
which are reset due to the FEC reset, and what locations the user must initialize before
enabling the FEC.
11-30
Pointer to start of transmit buffer descriptor queue.
— Reserved, should be cleared.
0000_0000_0000_0000
11 10
Table 11-29. R_BUFF_SIZE Field Descriptions
Name
—
R_BUFF_SIZE
—
MCF5272 User's Manual
Description
—
Read/Write
R_BUFF_SIZE
Read/Write
MBAR + 0xC18
Description
Reserved, should be cleared.
Receive buffer size.
Reserved, should be cleared.
4 3
—
0000
16
0