Measuring 30b CPU speed reduction

[cyrille de brébisson]

Hello,

whoa, I had no idea that this chat would spark that much debate... so let me try to clarify/cleanup a couple of things:

- The Atmel chip used in the 30b IS more energy efficient at lower clock speeds (ie, uses less energy to perform a calculation), for 2 main reasons:
- The clock can be generated using a very simple oscillator (think 2 not cells and a cap/resistance circuit which uses virtually no power), while the high speed is generated through a PLL (Phase Locked Loop) which is very power intensive (a non negligible fraction of a mA if my memory serves me well).
- The flash is not able to deliver data at the high CPU speed, so there is a 1 cycle delay on memory accesses. This means that it take more CPU cycles to execute a complex program at high speed than at low speed (ie, CPU cycles are wasted).

- replace the "car analogy" by "a non non hydrodynamic sold being propelled by an ideal engine through a fluid". In this case, moving it from point A to point B will take more energy at higher speed as the friction with the fluid increases.

Anyhow, the whole reason for the slow down is the fact that the battery does NOT like the long, high drain (they can heat up bad, especially if there is only 1 battery in the device), and that HP does state on the datasheet that the battery does last x months (I do not remember the exact number, under normal circumstances) and that HP needed to do what was necessary to make that happen. Plus, it's more ecological :-)

Cyrille