ITP700 Debug Port Design Guide

90 ITP700 Debug Port Design Guide

PASS FAIL Don’t

Care

ISSUE

Are the Resistance Values and Termination Voltages Listed in the table

above adhered to?

No bypass condition should allow the Pull-up resistance on TDI to be less

than 150 Ω.

Part 5 – Layout Issues

Below is a list of basic rules to keep in mind when routing the schematics. These guidelines are in

no means comprehensive or serve to replace the recommended layout guidelines in this document.

1. BPM[5:0]# should be routed in matched lengths as full speed Front Side Bus signals. There

should be only two terminations on the trace. One should be a passive resistor located just

beyond the debug port, and the other a passive resistor located just beyond the last agent on

the FSB. Note the flight time of the BPM signals from the closest processor agent on the Front

Side Bus to the debug port. This value will be important later. (Tbpm)

2. BCLK (n,p) should be routed with the same matched length as the clock to the rest of the

processor/chipset agents but with an additional flight time equal to the BPM signals flight

time from the closest processor agent on the front side bus to the debug port (Tbpm). Routing

in this manner will place you close to the optimal recovery point of the BPM#s using BCLK

and its added length. Fine adjustment may be necessary to place BPM# edges in the center of

the ITP Setup and Hold window (400 ps and 500 ps, respectively)

3. TCK should be routed in a star topology from the debug port (or buffer) with matching

lengths to each agent in the scan chain. The FBO feedback from the source of the scan chain

TCK(or FBI) to the ITP should have a flight time equal to the matched TCK paths plus the

flight time of the BPM signals from the closest processor agent on the Front Side Bus to the

debug port (Tbpm). If a buffer is used in the creation of TCK, it is recommended that FBO be

routed from an extra buffer to the FBO pin with a flight time calculated in the same method as

listed above.

4. TMS, like TCK, should also be routed in a star topology from the debug port with matching

lengths to each agent in the scan chain. Ideally these traces will be the same length as those of

TCK to each agent in the scan chain.