Boot fails when LRADC0 pin is in use

[kostas]

Dear All
I'm trying to setup an entry level temperature datalogger
I use IMX233 MAXI for development, while the target is to use IMX233 MICRO without any extra components
(besides a couple of resistors, thermistors and connectors)
Two A/D physical ports are available, LRADC0 and LRADC1.
I use two NTC10k thermistors, each one in its own resistor divisor circuit between 3.3VREG and ground.
During the initial tests, i used resistors in place of thermistors trying to estimate performance in certain conditions.
At this point i realized that when the voltage on LRADC0 pin is V3.3VREG/2 (about 1.65V) there is a boot failure at the very early stages (and far before any custom inisialization entry point)
On the other side, as long as LRADC0 is either floating or tied to 3.3VREG or even tied to GND boot sequence is normal.
The same tests on LRADC1 do not show any problem.

Booting sequence is as follows
[root@NetServer100+ regutil]# HTLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLFC
PowerPrep start initialize power...
Battery Voltage = 1.83V
No battery or bad battery               detected!!!.Disabling battery         voltage measurements./r/nLLCSep 19 201201:24:06
EMI_CTRL 0x1C084040
FRAC 0x92926192
init_ddr_mt46v32m16_133Mhz
power 0x00820710
Frac 0x92926192
start change cpu freq
hbus 0x00000003
cpu 0x00010001
LLLLLLLFCLJUncompressing Linux... done, booting the kernel.

Is there any idea on what might happen
I don't want to give up that easilly and use an additional A/D

Best Regards
Kostas

[Kean]

I encountered a similar problem, and eventually discovered the imx bootlet code reads LRADC0 as if it was a resistive divider keypad.  Certain voltages levels would then lead to "problems" with the boot process.  It was about 18 months ago, so I don't remember the exact details, but a Google search on something like "imx bootlets keypad" might help if you want more info.

[kostas]

Dear Kean,
Thanks a lot! I owe you!
You saved me a lot of time

Best Regards
Kostas