AMD K manual Potential Effect on System. The system hangs

Preliminary Information

AMD Athlon™ Processor Model 4 Revision Guide 23614K —October 2003

11 PLL Overshoot on Wake-Up from Disconnect Causes Auto-Compensation Circuit to Fail

Products Affected. A4, A5, A6, A7, A9

Normal Specified Operation. The AMD Athlon processor model 4 PLL should return to the normal operating frequency when reconnecting to the system bus after a disconnect where the PLL was reduced to a lower operating frequency.

Non-conformance.The AMD Athlon processor model 4 PLL can exceed the normal operating frequency when reconnecting to the system bus after a disconnect, causing a failure to maintain sufficient system bus I/O drive strength levels in the driver compensation circuit. The compensation circuit attempts to correct the drive strength, but if there is not sufficient time to perform this function, the system bus cannot operate properly.

Potential Effect on System. The system hangs.

Suggested Workaround. The event can be avoided through BIOS manipulation of the reconnect timing using the CLK_CTRL MSR. (See AMD Athlon™ and AMD Duron™ Processor CLK_CTRL MSR Settings, order# 24478, for exact values.)

The time for the PLL to overshoot can be greatly shortened to reduce it to a very small time period that does not enable the failure, and the time between the rampup and the reconnect to the system bus can be increased such that a failure in the compensation circuit has enough time to recover before reconnecting to the bus.

Resolution Status. Fix planned for a future revision.

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