MPC8544COMEDEV Freescale Semiconductor, MPC8544COMEDEV Datasheet - Page 901

• Manufacturer Part Number: MPC8544COMEDEV
• Description: KIT DEV EXPRESS MPC8544COM
• Manufacturer: Freescale Semiconductor
• Type: MPUr

Specifications of MPC8544COMEDEV

• Contents: Board
• For Use With/related Products: MPC8544
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

In practice a protocol stack or device driver can abuse PBQ by attempting to queue too much traffic onto
high priority rings. It is recommended that the highest priority ring should normally not be used at all
except for frames requiring the utmost urgent transmission. This allows emergency traffic to overtake
backlogged queues out of sequence.
15.6.5.2.2
eTSEC implements a modified weighted round-robin scheduling algorithm across all enabled TxBD rings
when TCTRL[TXSCHED] = 10. In MWRR, the weights in the TR03WT and TR47WT registers
determine the ideal size of each transmit slot, as measured in multiples of 64 bytes. Thus, to set a transmit
slot of 512 bytes, a weight of 512/64 or 8 needs to be set for the ring. In this mode TxBD rings 1–7 are
selected in round-robin fashion, whereas TxBD ring 0, if enabled with ready data for transmission, is
always selected in between other rings so as to expedite transmission from ring 0.
The scheduling decision is then achieved as follows:
Freescale Semiconductor
endloop
for ring = 1..7 and enabled(ring) loop
endloop
for ring = 1..7 and enabled(ring) loop
endloop
endloop
if priority_ring >= 0 then
endif
credit[ring] = 0;
if not ring_empty(0) then
endif
if not ring_empty(ring) then
endif
while credit[ring] > 0 loop
endloop
endif
ring = ring + 1;
while not ring_empty(priority_ring) loop
endloop
credit[0] = credit[0] + weight[0];
while credit[0] > 0 loop
endloop
credit[ring] = credit[ring] + weight[ring];
transmit_frame(ring);
credit[ring] = credit[ring] - frame_size;
if ring_empty(ring) then
endif
MPC8544E PowerQUICC III Integrated Host Processor Family Reference Manual, Rev. 1
Modified Weighted Round-Robin Queuing (MWRR)
transmit_frame(priority_ring);
transmit_frame(0);
credit[0] = credit[0] - frame_size;
if ring_empty(0) then
endif
credit[ring] = 0;
credit[0] = 0;
Enhanced Three-Speed Ethernet Controllers
15-169