Terminal connection to USB-UART interferes with other USB communication

[Linus234]

Hi there,

I am running Linux Mint 17.3 (i.e. Ubuntu 14.04) as guest on a Windows 7 host.



I have an FPGA (Altera Cyclone IV on DE0 Nano Board) running a system on chip (orpsoc).
(c.f. http://opencores.org/or1k/ORCONF2013_Wo ... n_DE0_Nano)
There is a USB-Cable that communicates with the FPGA's JTAG interface (USB-Blaster) to programm both the FPGA bitstream and the binaries for the SoC.
When I run the binary, I need to listen to the SoC's output via a UART breakout board connected to the FPGA's GPIOs.

On a nativ Linux system, everything works fine.

In the VirtualBox guest, however, the JTAG communication is not working any more, as soon as I open the terminal connection to the UART (e.g. with screen /dev/ttyUSB0 115200). By "not working" I mean that I get all kinds of strange error messages from the JTAG connected Telnet that seem to indicate that the data transmission is not successful.

It looks as if the UART-USB connection is somehow "jamming" the JTAG USB connection.

Any ideas how to narrow that down further and maybe even solve it?

Thanks in advance,
Linus

[socratis]

the JTAG communication is not working any more

Your chances of successfully controlling a USB debug interface (JTAG) from a VM, range from 0% to 0.1%. VMs don't really do physical hardware, but it kind of depends how finicky the device is about accurate timing. And that last word is the key word. Hardware in a VM has to go through another layer of software which most of the time makes things more complicated and prone to incorrect timing.

Thanks in advance, Linus

Shouldn't you be working on the kernel right now?
Sorry, couldn't resist

[Linus234]

Hey, thanks for the quick reply! Too bad, that my chances are that low.

In fact, I found out that it works when I use two spearate computers each running Linux in a VM: one establishes the terminal connection to the UART the other handles the JTAG debug interface...

But this is not ideal either. At least now I know that there is a good a reason to have Linux as a dual boot on my computer.

(I can now go back to working on the kernel...