Motorola PowerQUICC II MPC8280 Series Reference Manual page 1113

31.15.1.2 Example
Suppose the MPC8280 is connected to four 155 Mbps PHY devices and the maximum
transmission rate is 155 Mbps for the first PHY and 10 Mbps for the rest of the PHYs. The
BRG CLK should be set according to the highest rate. If the CPM clock is 133 MHz and
the BRG CLK is 66 MHz, the BRG should be programmed to divide the CPM clock by 181
to generate cell transmit requests every 362 system clocks:
For the 155 Mbps PHY, the FTIRR divider should be programmed to zero (the BRG CLK
is divided by one); for the rest of the 10 Mbps PHYs, the FTIRR divider should be
programmed to 14 (the BRG CLK is divided by 15).
See also Section 31.17.1, "Using Transmit Internal Rate Mode."
31.15.1.3 Internal Rate Programming Model
The programming sequence in TIREM = 0 mode is as follows:
1. Clear GFEMRx[TIREM]
2. Program FTIRRx
The programming sequence in TIREM = 1 mode is as follows:
1. Clear FTIRRx[TRM]
2. Set GFEMRx[TIREM]
3. Program FIRSRx_HI and FIRSRx_LO
4. Program FTIRRx
5. Program FIRPERx
If FTIRRx are set to generate same order of magnitude rates, setting round robin polling
mode is more adequate than fixed priority mode. To reduce the risk of transmit underrun if
there are a few PHYs with high internal rate and a number of PHYs with a low internal rate,
the fast PHYs should be assigned consecutive addresses starting at 0 and fixed priority
mode should be chosen.
31.15.1.4 FCC Transmit Internal Rate Port Enable Registers (FIRPERx)
This register enables internal rate transmission for PHYs[0-30]. It is valid only if
GFEMR[TIREM] = 1. If a PHY is not enabled in FIRPER, all TxClav indications from that
PHY will be masked. The user should configure FIRPER according to the PHY addresses
which are being used on the UTOPIA bus and should not enable PHYs with addresses
larger then the last PHY address set by FPSMR[Last PHY]. PHYs can be enabled or
disabled at any time—for example, if a TIRU event has occurred.
MOTOROLA Chapter 31. ATM Controller and AAL0, AAL1, and AAL5
Freescale Semiconductor, Inc.
Transmission Rate Modes—External, Internal, and Expanded Internal
( × (
66MHz 53 8
------------------------------------------------- -
155.52Mbps
For More Information On This Product,
Go to: www.freescale.com
× ) )
= 181
31-99