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Kevin Redon kevredon at mail.tsaitgaist.infoThanks for the fast analysis
>
> 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.
>
> 3) It might be nice to have an ADC input connected to the VCC_OUT line,
> to be able to measure the SIM card supply voltage as it is output
> by the phone. ADCREF of course would have to be connected, too.
I will add it.
>
> 4) It is generally good 'style' to connect the nWP to some I/O line of
> the CPU (together with a pull-down).
ack
> 5) I think the IN/OUT naming is a bit misleading. E.g. "VCC_OUT" is the
> source of the VCC power, i.e. the phone. It may be better to call
> the signals leading to the phone {VPP,I/O,CLK,RST,VCC}_PHONE and the
> signals leading to the sim {VPP,I/O,CLK,RST,VCC}_SIM
ack
>
> 6) The USB pull-up mechanism is missing. This is required for properly
> signalling a USB bus reset to the host controller. Please refer to
> the OpenPCD schematics for an example circuit. It just requires one
> transistor and some resistors. It has also proven useful to connect
> the nRESET to that pull-up circuit to make sure a cpu-reset leads to
> a bus reset as well.
>
> 7) A 5.6V Zener diode makes sense as over-voltage protection at the USB
> 5V power supply line
I will have a look for it
>
> 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.
>
> 9) I would only use a jumper for the TEST singal, as we probably only
> need it very rarely during sam7dfu testing/porting. After that, we
> will use USB DFU for updates
ack
>
> 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
>
> Regards,
> Harald
WiP,
Kevin