How to use Microblaze debug on an Arty A7?

[Allan Flippin]

     I'm looking through Xilinx file pg115-mdm.pdf about the Microblaze debug module.  If I use a Microblaze core, I'm sure I'll need some debug capability.  But I'm not sure how the MDM can be used on an Arty board.  MDM seems to be a JTAG-based debugger.  I think it uses the FPGA's JTAG pins.  I know the Adept2 utility uses the USB connection to access JTAG through the FTDI chip.  But "JTAG debugging" isn't on the list of what Adept2 does.  In the Adept SDK, I see information about an API to access JTAG.  That would probably work, but I'd rather not be debugging debug system software while I'm trying to debug my Microblaze software.  Another issue is if I use the existing USB cable for JTAG debugging, will I have trouble running the UART bridge interface?

     If I get a Digilent JTAG-HS2 and use that for JTAG, will that solve the problems?  The Vivado software would know how to use the JTAG on this adapter for its debugger right?  And the UART bridge would still work as usual.

     Do I have it right?  Or am I missing something stupid.  I just want to make sure there's no problem with Microblaze debugging that makes it too hard to use in my application.  Thanks.

Allan

[kwilber]

The Arty board has all the JTAG circuitry plus a USB UART on board. You don't need a special cable - just use a good quality USB to micro USB cable.

In the Vivado IPI, when you instantiate a Microblaze core, the MDM is automatically added and connected by block automation. 

The Xilinx SDK debugger will automatically use the MDM for debugging. You don't have to do anything other than start your program in debug mode.

It sounds to me like going through one of the numerous online tutorials would help you get your bearings. Digilent has several including this one.Prolific blogger Adam Taylor also starts a series of posts on the Arty here. And if you like watching videos, Jeff Johnson at FPGADeveloper.com has this one.

[jpeyron]

Hi @Allan Flippin,

The USB UART connector/programming circuit on the Arty works with microblaze allowing you to debug in SDK. If you were wanting to use the JTAG HS2 as an alternative for configuring/debugging and running an application for the Arty in SDK you can do that to. I just made a simple GPIO/uart project using the JTAG HS2/JTAG connector to program the fpga and run the application which worked with one exemption.  Using the JTAG HS2  did not facilitate a com port for serial communication.

best regards,

Jon

[Allan Flippin]

Thanks for your replies.  Sure, if I can use the single USB cable for debug plus device configuration, I'll be glad to do it!  I just didn't understand how Vivado would know about the USB-to-FTDI chip link for the Arty A7.  Isn't this why we require Adept for configuration instead of doing it directly by Vivado?  Also, I'm I'm using a UART bridge for communicating with the Arty A7, wouldn't debug wreck that connection?  I'll look at the videos, but I doubt this sort of thing is covered, PC communication with the Arty boards is not something that most people do.

Allan

[kwilber]

The Digilent proprietary USB UART/JTAG circuity allows for simultaneous jtag and uart use.The board appears as two serial ports. Vivado and the SDK automatically find the jtag port and you can use a communication app like TeraTerm using the other port. The "hello world" example you can create in the SDK demonstrate that. Serial communication with the pc is fairly common.

[Allan Flippin]

kwilber

     Thanks!  That's what I need to know for now.  I'm solidifying my choice of board and trying to locate anything which can't work with the board that I choose.  I've been leaning towards Arty A7, and this was the last potential gotcha I have to check.  I'll move forward now and assume Arty A7 is it.  I'm still trying to get my company to install Vivado on my PC, or I would have been able to look myself directly.

Allan