Re: Raspberry Pi support for Rev-2 & BL

Hi Paul,

On 22.01.2013 20:37, paul_c wrote:
> 
> Hi Markus
> 
> On Tuesday 22 January 2013, Markus Dolze wrote:
>> There is one point left I would like to know your opinion about:
>>
>> The default pin for driving the backlight is GPIO28 which is routed
>> to P5. As P5 is not available on Rev 1 boards and not populated on
>> Rev 2 boards, I would like to assign the default pin to a GPIO line
>> available on P1 - currently I prefer GPIO17 which is P1-11.
> 
> There are two spare GPIO pins in the ALT-0 group that are currently 
> unused and common to both board revisions - GPIO17 and GPIO22.
> Using any of the other GPIO pins risks conflicts if the Serial/I2C/SPI 
> kernel drivers are loaded.... Which raises a (minor) problem for EN 
> currently driven by GPIO8 - This is used by the SPI driver if it is 
> loaded.

For that reason I wanted to use GPIO17. I recognized GPIO08 (and GPIO07)
having alt-0 functions for SPI, but was not aware there is a driver this.

> 
>> Any objections?
> 
> No objections to GPIO17 being used, could you switch EN to the remaining 
> unused GPIO22 - Perhaps a note in the docs about possible GPIO 
> conflicts when kernel drivers are loaded might be in order.

I am vary about this. GPIO08 has the advantage that - if no backlight is
used - all LCDd pins are on the same one row. You could use a simple
single row connector then.

Adding a warning in the documentation does no harm anyway.

BTW: When I tried to use the switchable backlight on my display, it
didn't work. Likely because of the 3.3 V signal level vs. 5 V power
supply. Can you point me to a working circuit?

Regards,
Markus