Re: SIMtrace v0.6 schema

Hi Kevin, thanks for posting your most recent schematics. On Sat, May 07, 2011 at 10:12:23PM +0200, Kevin Redon wrote: 1) Regarding dexters mail: I defintely would want JTAG, it helps a lot for debugging. We don't have to solder the connector for production units after R&D has finished. 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? It may be worth putting both footprints (for the 6-pin cable and the 2.5mm jack) on the PCB. This way we can later still decide which one to place on the board. 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. 4) It is generally good 'style' to connect the nWP to some I/O line of the CPU (together with a pull-down). This way the memory is write-protected by default. Only if the CPU sets the GPIO to high, it can write to the flash. 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 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 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. 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 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) Regards, Harald -- - 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)