[linux-cirrus] Re: EP9302 on-chip ADC
- From: Robert Ernst <r.ernst@xxxxxxxx>
- To: linux-cirrus@xxxxxxxxxxxxx
- Date: Thu, 2 Mar 2006 18:38:00 +0100
> We are trying to use the on-chip ADC of a custom board based on Cirrus
> Logic EP9302. The User's Guide of EP9301 stated that the ADCEN bit should
> be set high and ADCPD should be set low in order to use ADC. We tried to
> write the device config register to set those bits, but for some reason
> the bits would always be reset to it's original value.
A lot of the Syscon registers may only be written when you unlock them by
writing 0xAA to the Syscon SWLock register first, _and_ you have to make sure
that no Syscon register access occurs between unlocking and writing, for
example:
unsigned long reg;
cli();
reg = inl(SYSCON_ADCCLKDIV);
SysconSetLocked(SYSCON_ADCCLKDIV, reg | SYSCON_ADCCLKDIV_ADCEN);
reg = inl(SYSCON_DEVCFG);
SysconSetLocked(SYSCON_DEVCFG, reg | SYSCON_DEVCFG_ADCEN);
reg = inl(SYSCON_DEVCFG);
SysconSetLocked(SYSCON_DEVCFG, reg & ~SYSCON_DEVCFG_ADCPD);
sti();
Turning off the interrupts makes sure that there is no race condition with
other processes that might try to change the SYSCON_* registers at the same
time, and using the SysconSetLocked() macro takes care of unlocking.
Note: there is a lock register for the ADC channel select register, too!
hope that helps,
Robert
Other related posts:
