MPC8313CZQADDC Freescale Semiconductor, MPC8313CZQADDC Datasheet - Page 892

• Manufacturer Part Number: MPC8313CZQADDC
• Description: Microprocessors - MPU 8313 REV2.2 PB NO EN EXT
• Manufacturer: Freescale Semiconductor

Specifications of MPC8313CZQADDC

• Processor Series: MPC8313
• Core: e300
• Data Bus Width: 16 bit
• Maximum Clock Frequency: 133 MHz
• Program Memory Size: 16 KB
• Data Ram Size: 16 KB
• Interface Type: I2C
• Mounting Style: SMD/SMT
• Package / Case: PBGA
• Number Of Programmable I/os: 32
• Number Of Timers: 4

Enhanced Three-Speed Ethernet Controllers
15.6.4.3.1
PBQ is the simplest scheduler decision policy. The enabled TxBD rings are assigned a priority value based
on their index. Rings with a lower index have precedence over rings with higher indices. For example,
TxBD ring 0 has higher priority than TxBD ring 1, and TxBD ring 1 has higher priority than TxBD ring
2, and so on.
The scheduling decision is then achieved as follows:
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.
15.6.4.3.2
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:
15-174
loop
endloop
for ring = 1..7 and enabled(ring) loop
endloop
for ring = 1..7 and enabled(ring) loop
priority_ring = null;
ring = 0;
while priority_ring == null and ring <= 7 loop
endloop
if priority_ring >= 0 then
endif
credit[ring] = 0;
if not ring_empty(0) then
endif
if enabled(ring) and not ring_empty(ring) then
endif
ring = ring + 1;
while not ring_empty(priority_ring) loop
endloop
credit[0] = credit[0] + weight[0];
while credit[0] > 0 loop
endloop
MPC8313E PowerQUICC™ II Pro Integrated Processor Family Reference Manual, Rev. 2
Priority-Based Queuing (PBQ)
Modified Weighted Round-Robin Queuing (MWRR)
priority_ring = ring;
transmit_frame(priority_ring);
transmit_frame(0);
credit[0] = credit[0] - frame_size;
if ring_empty(0) then
endif
credit[0] = 0;
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