Posted on August 16, 2005 at 09:44I am having big trouble switching from 48mhz clock to the 32khz crystal oscillator.
I am using the following code to switch the the CLK_AF source and then check the status to make sure it has switched as per the data sheet
''Note: To check if the selection has actually occurred, check that CKAF_ST is set. If no Real Time Clock is present, the selection will not occur.''
GPIO0->PD |= BIT16_13;
do {
RCCU->CCR |= 0x00000004;
}while( (RCCU->CFR &0x00000004) ==0 );
GPIO0->PD &= ~BIT16_13;
The problem is it appears the the clock source does indeed switch as can be seen from the clockout pin, however it can sometimes take as long as 8-10 seconds to exit the loop. This has been verified by measuring the pulse on GPI0.13. Sometimes it will switch without any problems.
The CKAF_SEL bit in the RCCU_CFR register is obviously not being set correctly ! Is this a silicon bug ? There seems no point in checking this bit as it doesnt acurately indicate if the clock switch has actually occured. Also it seems to be different between 2 different chips.
Has anyone else experienced similar problems ?
