Freescale Semiconductor MPC8260 - Manual (Page 1204)

Fast Ethernet Controller
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
35-8 Freescale Semiconductor
When an external CAM is used for address filtering, users can choose to either discard rejected frames
(FPSMR[ECM] = 0) or receive rejected frames and signal the CAM miss in the RxBD (FPSMR[ECM] =
1).
NOTE
The bus atomicity mechanism for CAM accesses may not function correctly
when the CPM performs a DMA access to an external CAM device. This
only impacts systems in which multiple CPMs will access the CAM.
35.8 Ethernet Parameter RAM
For Ethernet mode, the protocol-specific area of the FCC parameter RAM is mapped as in Table 35-2 .
Table 35-2. Ethernet-Specific Parameter RAM
Offset
1
Name Width Description
0x3C STAT_BUF Word Buffer of internal usage
0x40 CAM_PTR Word CAM address. For FCC Fast Ethernet operation the CAM should be located on the
same bus as the data buffers.
0x44 C_MASK Word Constant MASK for CRC (initialize to 0xDEBB_20E3). For the 32-bit CRC-CCITT.
0x48 C_PRES Word Preset CRC (initialize to 0xFFFF_FFFF). For the 32-bit CRC-CCITT.
0x4C CRCEC 2 Word CRC error counter. Counts each received frame with a CRC error. Does not count
frames not addressed to the station, frames received in the out-of-buffers condition,
frames with overrun errors, or frames with alignment errors.
0x50 ALEC
2
Word Alignment error counter. Counts frames received with dribbling bits. Does not count
frames not addressed to the station, frames received in the out-of-buffers condition, or
frames with overrun errors.
0x54 DISFC 2 Word Discard frame counter. Incremented for discarded frames because of an out-of-buffers
condition or overrun error. The CRC need not be correct for this counter to be
incremented.
0x58 RET_LIM Hword Retry limit (typically 15 decimal). Number of retries that should be made to send a
frame. If the frame is not sent after this limit is reached, an interrupt can be generated.
0x5A RET_CNT Hword Retry limit counter. Temporary decrementer used to count retries made.
0x5C P_PER Hword Persistence. Allows the Ethernet controller to be less persistent after a collision.
Normally cleared, P_PER can be from 0 to 9 (9 = least persistent). The value is added
to the retry count in the backoff algorithm to reduce the chance of transmission on the
next time-slot. Using a less persistent backoff algorithm increases throughput in a
congested Ethernet LAN by reducing the chance of collisions. FPSMR[SBT] can also
reduce persistence of the Ethernet controller. The Ethernet/802.3 specifications
permit the use of P_PER.
0x5E BOFF_CNT Hword Backoff counter
0x60 GADDR_H Word Group address filters high and low are used in the hash table function of the group
addressing mode. The user may write zeros to these values after reset and before the
Ethernet channel is enabled to disable all group hash address recognition functions.
The
SET GROUP ADDRESS command is used to enable the hash table. See
Section 35.13, “Hash Table Algorithm .”
0x64 GADDR_L Word