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Harald Welte laforge at gnumonks.orgHi Kevin,
On Sun, May 08, 2011 at 01:40:46PM +0200, Kevin Redon wrote:
> > 2) It might be an idea to use a 2.5mm jack (like Compal phones) for the
> > DBGU, instead of the FTDI-6pin-header. I guess more people in and
> > around the Osmocom projects have a T191 cable than a FT232 cable with
> > the 6-pin header. What do the others think?
>
> I would choose jack 2.5 only, but I will put both.
ok, thanks.
> > 8) The two 47uF capacitors at the 3.3V line and the 22uF capacitor at
> > the 5V line might be above the USB specifications for capacitive
> > load. See Section 7.2.4.1 of the USB spec, where I believe it says
> > you can only put a cumulative capacitance of 10uF at the downstream
> > end of a Vbus. We might ignore that, or use something like a
> > LM3525 (or even a TI TPS2151 which is a LDO with built-in in-rush
> > current limiter). OpenPCD1 v0.4 is not being sold anymore exactly
> > due to this problem.
>
> didn't know than, I will change the ld1117 with a tps73633 (less
> expensive then TPS2151, and fits perfectly).
ok.
> I don't understand why the capacitor at the 3.3v line affect USB, but I
> will minimize it.
The problem is that in power-on, the capacitive load on the 3.3V side
normally also becomes visible as a capacitive load on the 5V side (as
the regulator basically is 'switched through' at the moment you have the
raising edge of supply power.
> > 10) However, it is useful to have a push-button for DFU-mode activation,
> > this is a simple switch between Vcc and a GPIO. Normally, DFU is
> > activated over USB itself. However, if the firmware is dead, this
> > BOOTLOADER switch can help with recovery (once again, see OpenPCD)
>
> I will take the openPCD design
If you look at the OpenPCD design, the I/O pin has a pull-down, and the
switch goes to Vcc. In your v0.7 schematics you now have no pull-down
and a series resistor for Vcc. I think we should use the OpenPCD way as
it is known working.
--
- Harald Welte <laforge at gnumonks.org> http://laforge.gnumonks.org/
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