[ltp] How to "step-up" the CPU back to full speed on AC?

[Teo Hong Siang]

Hi, I have an X21, which is a PIII-700 with Speed Step. Here's my
problem: 
When I go from AC to batt, the CPU automatically steps down to a series
of lower freqs, starting at 500MHz. `cat /proc/cpu` shows the current
CPU speed, which can be as low as 200+ MHz on low batt. This is fine, as
it saves batt life. 
But when I plug back to AC, I notice that the CPU speed never steps back
up to full tilt at 700MHz. It kind of get stuck at the last freq. 
I tried using `tpctl -pma=high` but no effect. 

Any help?