Slow clock oscillator

[Konstantin B]

Hello,
I have played around with the Linuxstamp II and am working on
designing a similar board that also uses the AT91SAM9G20. I was
wondering whether the slow clock oscillator on the XIN32 and XOUT32
lines is mandatory to include for the operation of the board?
The datasheet seems to suggest that the main oscillator is disabled
after reset and it switches to use the slow clock by default.

Thank you,
Konstantin

[Michael]

The embedded SAM-BA ROM code on the 9x25 chip switches to the internal
32 KHz RC oscillator (not external crystal, but internal RC) to do an
approximate measurement of the actual frequency of the external
(presumed) 12 MHz oscillator (crystal). This does not mean you have
to have a 32 KHz crystal hooked up to the chip. If you do, you can
enable it later for more accurate watchdog and RTC behavior. I
presume the 9g20 does the same trick. This is actually very smart,
and you can run the chip without any external crystal at all if you
are not too concerned about absolute clock frequency (subsystems like
USB or Ethernet might get torqued-up, however, if you were very far
from 12 MHz).

- Michael