Receive Buffer Size Register (Emrbr) - STMicroelectronics SPC572L series Reference Manual

RM0400
Offset: 184h
0 1 2 3
R
W
Reset — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — —
Figure 711. Transmit Buffer Descriptor Ring Start Register (ETDSR)
Field
X_DES_START
48.4.23

Receive Buffer Size Register (EMRBR)

The EMRBR dictates the maximum size of all receive buffers. 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. To properly
align the buffer, EMRBR must be evenly divisible by 16. To ensure 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 is undefined at reset and must be initialized by the user.
Offset: 188h
0 1 2 3
R 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
W
Reset — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — —
Field
Maximum size of receive buffer size in bytes. To minimize bus utilization (descriptor fetches),
set this field to 256 bytes (10h) or larger.
10h
R_BUF_SIZE
11h
...
7Fh
4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Table 721. ETDSR field descriptions
Pointer to start of transmit buffer descriptor queue.
4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Figure 712. Receive Buffer Size Register (EMRBR)
Table 722. EMRBR field descriptions
256 + 15 bytes (minimum size recommended)
272 + 15 bytes
2032 + 15 bytes. The FEC writes up to 2047 bytes in the receive buffer. If data larger
than 2047 is received, the FEC truncates it and shows 7FFh in the receive descriptor
X_DES_START
Description
Description
DocID027809 Rev 4
Fast Ethernet Controller (FEC)
Access: User read/write
Access: User read/write
0 0 0
R_BUF_SIZE
0 0
0
1319/2058
1358