Is it physically possible to output from UART_B_TX while still debugging via JTAG?
Specifically, I see that TRST_N is mux'd with UART_B_TX. TRST_N is one of those JTAG pins which is technically optional (since a TAP reset can be asserted via either TRST_N or by holding TMS high for five clock cycles).
The main documentation warns that disabling JTAG and assigning the pins to UART_B locks out JTAG--which is a good warning. But I'm wondering if that doesn't apply if we only reassign pin TRST_N.
I'm asking specifically "is this possible from a Quark D2000 perspective", and not in relation to the current build of OpenOCD. I am working on custom JTAG debugger software for Quark micros--so there are no software limitations here.
Thanks for your interest in the Intel Quark Microcontroller Platform.
This is an interesting question! Reading through the datasheet (http://www.intel.com/content/dam/www/public/us/en/documents/datasheets/quark-d2000-datasheet.pdf http://www.intel.com/content/dam/www/public/us/en/documents/datasheets/quark-d2000-datasheet.pdf ) in Section 3.3, it states that using the Quark in user mode should let you configure individually each pin in the 4 user modes.
Now I can't guarantee that this will work, since you are changing interfaces, you will have to test it to see if it works.
Hope you find this information useful, have a nice day!
Thanks Jose. I'll give it a try!
When I'm done with the debugger, would it be appropriate to show off the cool stuff we're building with Quark here--or is this more of a forum for "questions about the processor only"?
I'll also try to report back as to whether or not I was successful using the /TRST pin as a TX-only UART without disabling JTAG. We're specifically trying to use the pin that way to redirect printf output (so that we can use the USB port for both JTAG debug and "printf output" debug). I'm hoping that this is specifically what the processor designers had in mind when they put UARTB_TX on the optional JTAG reset pin.
This will be a fun project.