> From: Paul Walmsley [mailto:[email protected]] > Sent: Thursday, April 23, 2009 3:53 AM > To: Woodruff, Richard
> > 4. Current PM code didn't enable the maximum clock (i.e. CPU: 600Mhz) > > according to the comment as below: > > > > /* Avoid registering the 120% Overdrive with CPUFreq */ > > prcm = mpu_opps + MAX_VDD1_OPP - 1; > > > > But in some cases, we should use 600Mhz for multimedia application. > > And, even thought we enable the maximum clock, CPU frequency seldom > > goes into maximum clock. I think we don't have to avoid registering > > the max OPP. > > Do you know if this restriction can be lifted now, i.e., can the silicon > run at VDD1 OPP1 100% of the time and meet the device lifespan targets? So, there have been some characterization changes which give more leeway for software usage off overdrive. What you found before was guarantees against typical mobile usage for a few classes of devices. This was done using a mix of OPPs with the majority of active time in lower OPPs and inactive time in low idles (optimal usage for mix of typical operations, this is the way you would want to run ideally). Against this and many more variables, reliability data was validated and published. Recently there was some change to also measure active time at max overdrive for same usage mix. This resulted in still meeting lifetime goals for typical usage. This can translate to a smart phone maker of being able to use overdrive as they see fit and still have long life (assuming they can supply adequate power and still dissipate what ever additional heat there is). This is still not 100% of the time in active mode. I suspect TI will continue to create parts for certain markets when the need is there. The part might be nearly identical but the way it's rated (with chip binning and other tricks) will allow different guarantees. This fits well with mobile business customer needs. As an open source individual owner of a device, you might do things in a non-typical way. You are free to do this. Depending on which base chip variant you are using, its life may have some impact (or not). Your chip likely will still last many years. The phone or other device might die first. All that said, today personally, I feel much more comfortable exposing overdrives in the reference code. Mobile users and their devices which actually sleep at night should be pretty safe. Watch data sheets for details :) Regards, Richard W.
