A small contribution and a big question (timer/keyboard)

[cyrille de brébisson]

Hello,

in G2, the ticks is derived from a CPU clock (counter), itself based on the CPU buss clock, which is itself based on a PLL (Phase Locked Loop, ie a way to generate high frequency based on a lower frequency) based on the main CPU oscillator. I do NOT remember if this oscillator is based on a cristal or an oscillating circuit, but PLL are not always very accurate...
I did calibrate this on my prototype making it run 10h and I had less than 10s error at the end, so less than 0.03%... it is interesting that you are finding something different, I guess it shows variation from chip to chip, or maybe temperature sensitive...

The ticks counter of the G2 is also the clock which is used for thread switching, meaning that every ms, the CPU will check if it needs to switch from one thread to another... Luckily enough, unless USB is plugged in, prime G2 only runs 3 threads (from memory). The main app thread, the alarm thread (alarm as in internal timers) and the usb monitoring thread, which is sleeping waiting for a usb plug event...

In comparison, Prime G1 had over 10 threads!


The RTS is based on its own 32Khz crital if I remember well and should be as accurate as any watch....

Cyrille