8 May
2011
8 May
'11
7:55 p.m.
Hi Kevin,
On Sun, May 08, 2011 at 01:40:46PM +0200, Kevin Redon wrote:
ok, thanks.
ok.
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(a)gnumonks.org> http://laforge.gnumonks.org/
============================================================================
"Privacy in residential applications is a desirable marketing option."
(ETSI EN 300 175-7 Ch. A6)
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. 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). 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