Motorola MPC860 PowerQUICC User Manual page 761

Table 28-1. SCC Ethernet Parameter RAM Memory Map (Continued)
1
Offset Name
0x4C MINFLR
0x4E MAXD1
0x50 MAXD2
0x52 MAXD
0x54 DMA_CNT
0x54 MAX_B
0x58 GADDR1
0x5A GADDR2
0x5C GADDR3
0x5E GADDR4
0x60 TBUF0_DATA0 Word
0x64 TBUF0_DATA1 Word
0x68 TBUF0_RBA0 Word
0x6C TBUF0_CRC
0x70 TBUF0_BCNT Hword
0x72 PADDR1_H
0x74 PADDR1_M
0x76 PADDR1_L
0x78 P_PER
0x7A RFBD_PTR
0x7C TFBD_PTR
MOTOROLA
Width
Hword Minimum frame length register. The Ethernet controller checks the incoming
frameÕs 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.
Hword Max DMAn 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
Hword
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.
Hword Rx max DMA.
Hword Rx DMA counter. A temporary down-counter used to track frame length.
Hword Maximum BD byte count.
Hword Group address Þlter 1Ð4. 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
command is used to enable the hash table.
ADDRESS
Save area 0Ñcurrent frame.
Save area 1Ñcurrent frame.
Word
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.
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.
Hword Rx Þrst BD pointer.
Hword Tx Þrst BD pointer.
Chapter 28. SCC Ethernet Mode
Part V. The Communications Processor Module
Description
SET GROUP
28-13