Thanks for the fast analysis
- 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.
- 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.
- It is generally good 'style' to connect the nWP to some I/O line of the CPU (together with a pull-down).
ack
- 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
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.
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
- 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.
- 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
- 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