Introducing the Freerunner Navigation Board

[Christoph Mair]

On Sunday 02 May 2010 17:57:49 Stefan Schmidt wrote:
> Hello.
> 
> On Sun, 2010-05-02 at 17:42, Christoph Mair wrote:

> > Unfortunately the NOR bootloader does not work when both, pressure sensor
> > and navigation board, are connected (somebody knows why?). :)
> 
> Wild guess. You are not (ab-)using the H-TP4711 testpad which is pin 32 on
> the debug connector? That one is the write protect disable pin for the
> NOR.

No, during my tests I just connected both devices to the aux-switch (for 
power) and to to the I2C bus. Then the NOR u-boot did not start when I pressed 
the aux key (at least it did not enable the display). Disconnecting one of the 
bus lines (SCL or SDA) or the power supply fixed the problem. I guess this may 
be because NOR u-boot uses a slower frequency than the linux kernel, but I 
can't come up with a meaningful expanation for this.

I even increased the bus capacitance for one line by adding a 400pF capacitor 
between SCL and GND. Normally this is the stupiest thing to do, but it "fixed" 
the NOR u-boot with the tradeoff that Linux did not boot. :P

The wiki mentions possible problems 
(http://wiki.openmoko.org/wiki/I2C#Powering_additional_I2C_devices), but 
excludes the NOR u-boot.

Best regards,
  Christoph