Freescale Semiconductor MPC8260 User Manual
Page 792
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SCC Ethernet Mode
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
25-8
Freescale Semiconductor
0x4C
MINFLR
Hword Minimum frame length register. The Ethernet controller checks the incoming
frame’s length against MINFLR (typically 64 decimal). If the received frame is
smaller than MINFLR, it is discarded unless PSMR[RSH] is set, in which case,
SH is set in the last BD for the frame. For transmitting a frame that is too short,
the Ethernet controller pads the frame to make it MINFLR bytes long, depending
on how PAD is set in the TxBD and on the PAD value in the parameter RAM.
0x4E
MAXD1
Hword Max DMA
n
length register. Gives the option to stop system bus writes after a
frame exceeds a certain size. However, this value is valid only if an address
match is found. The Ethernet controller checks the length of an incoming Ethernet
frame against this user-defined value (usually 1520 decimal). If this limit is
exceeded, the rest of the incoming frame is discarded. The Ethernet controller
waits until the end of the frame or until MFLR bytes are received and reports the
frame status and the frame length in the last RxBD.
MAXD1 is used when an address matches an individual or group address.
MAXD2 is used in promiscuous mode when no address match is detected. In a
monitor station, MAXD2 can be much less than MAXD1 to receive entire frames
addressed to this station, but only the headers of the other frames are received.
0x50
MAXD2
Hword
0x52
MAXD
Hword Rx max DMA.
0x54
DMA_CNT
Hword Rx DMA counter. A temporary down-counter used to track frame length.
0x56
MAX_B
Hword Maximum BD byte count.
0x58
GADDR1
Hword Group address filter 1–4. Used in the hash table function of the group addressing
mode. 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.
0x5A
GADDR2
0x5C
GADDR3
0x5E
GADDR4
0x60
TBUF0_DATA0
Word
Save area 0—current frame.
0x64
TBUF0_DATA1
Word
Save area 1—current frame.
0x68
TBUF0_RBA0
Word
0x6C
TBUF0_CRC
Word
0x70
TBUF0_BCNT
Hword
0x72
PADDR1_H
Hword The 48-bit individual address of this station into this location. PADDR1_L is the
lowest order hword and PADDR1_H is the highest order hword.
0x74
PADDR1_M
0x76
PADDR1_L
0x78
P_PER
Hword Persistence. Lets the Ethernet controller be less aggressive after a collision.
Normally, 0x0000. It can be a value between 1 and 9 (1 is most aggressive). The
value is added to the retry count in the backoff algorithm to reduce the chance of
transmission on the next time slot.
Note: Using P_PER is fully allowed in the Ethernet/802.3 specifications. A less
aggressive backoff algorithm used by multiple stations on a congested Ethernet
LAN increases overall throughput by reducing the chance of collision.
PSMR[SBT] offers another way to reduce the aggressiveness of the Ethernet
controller.
0x7A
RFBD_PTR
Hword Rx first BD pointer.
Table 25-1. SCC Ethernet Parameter RAM Memory Map (continued)
Offset
1
Name
Width
Description