Motorola MCF5282, MCF5281 Receive Buffer Size Register Emrbr, Etdsr Field Descriptions, Rbufsize

Programming Model

Table 17-34. ETDSR Field Descriptions

Bits	Name	Descriptions
31–2	X_DES_START	Pointer to start of transmit buffer descriptor queue.
1–0	—	Reserved, should be cleared.

17.5.4.23 Receive Buffer Size Register (EMRBR)

The EMRBR is a 9-bit register programmed by the user. The EMRBR register dictates the maximum size of all receive buffers. Note that because receive frames will be 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, EMRBR must be set to RCR[MAX_FL] or larger. The EMRBR 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 EMRBR be greater than or equal to 256 bytes.

The EMRBR register does not reset, and must be initialized by the user.

Field

Reset

R/W

Field

Reset

R/W Address

31 16

—

Uninitialized

R/W

15	11	10	4	3	0
	—		R_BUF_SIZE		—

Uninitialized

R/W

IPSBAR + 0x11B8

Figure 17-26. Receive Buffer Size Register (EMRBR)

Table 17-35. EMRBR Field Descriptions

Bits	Name	Descriptions
30–11	—	Reserved, should be written to 0 by the host processor.
10–4	R_BUF_SIZE	Receive buffer size.
3–0	—	Reserved, should be written to 0 by the host processor.

17-44 MCF5282 User’s Manual MOTOROLA