Power-saving

[lpcware]

Content originally posted in LPCWare by Muis on Sat Dec 08 05:59:46 MST 2012
I need some guidelines to optimize my firmware for low power usage. One of the most obvious are:

- Disable unused pheripals
- Run the CPU at a lower clockrate
- Call __WFI instruction often

When looking for other options, I came across the 'power profiles' in the manual. One of them is PWR_EFFICIENCY.

"This setting was designed to find a balance between active current and
the CPU’s ability to execute code and process data. In this mode the device outperforms
the default mode both in terms of providing higher CPU performance and lowering active
current."

Can someone give a description what actually happens behind the scenes when you disable this? Does it have any downsides? If not, why is PWR_EFFICIENCY not enabled by default?

[lpcware]

Content originally posted in LPCWare by Daniel Widyanto on Tue Dec 18 23:48:39 MST 2012
Hi,

We cannot provide you any details for the reason. Just don't use the PWR_EFFICIENCY if you use USB.

[lpcware]

Content originally posted in LPCWare by Muis on Thu Dec 13 02:06:05 MST 2012
But the manual states that you cannot USB with PWR_EFFICIENCY enabled. So why is this? Because if the reason is that timer accuracy is decreased (for example), I'd like to know, because my project relies heavily on that.

[lpcware]

Content originally posted in LPCWare by Daniel Widyanto on Mon Dec 10 20:53:01 MST 2012
Well that information is classified ;-)

We've run some tweaking in our internal IPs to achieve better power / performance, and we don't want our competitor nor our customer messing around with the system's internal configuration. Of course if you are doing medical / aerospace / military application, you can always approach any of NXP distributors to liaise NDA agreement with NXP to get the detailed information.

Downsides : None so far. In fact, we have received good review from our major customers.

The reason why it's not enabled by default: Because we want to have the specification in the datasheet similar to the older generation (eg LPC111x/301,  LPC111x/302, etc). Changing the parameter in datasheet would require our customers to do qualification testing again, and we need to sync our manufacturing site for the new parameters testing. So we'll let the power profile as option for customers who want it (or not wanting it for compatibility reason).