USB Port on J3

[victagayun]

Will J3 USB port be utilized in the near future? Why was this not populated?

[Kristoff]

Hey victagayun,

Early on in the OpenScope MZ design we considered several options for 'wired' communication from WFL to OpenScope MZ.  The PROG USB port goes through an FTDI chip and provides access to program the PICMZ microcontroller on the board.  This port can also be used for UART communication with the PICMZ.  The other USB port was routed to the PICMZ to enable the OpenScope MZ to act as a USB device (Mass Storage / HID / Ethernet over USB, etc).   

One of the major challenges with WaveForms Live and OpenScope MZ was communication from the browser to the hardware, especially in the 'wired' configuration since all browsers sandbox applications from the system and connected hardware (some more than others).  We considered having OpenScope MZ show up as a virtual ethernet device so WFL was always talking to a network device, even in wired mode.  We considered having the OpenScope MZ show up as a mass storage device and generating data buffers as files that you could GET and POST.  In the end there were two main reasons we went with UART communication over the PROG port rather than enumerating OpenScope MZ as a USB device:

1. We're pushing the PICMZ to it's limits.  Keith likes to joke that we're using 9 of the 8 DMA's (since one is shared between two instruments).  Between parsing JSON commands, servicing the network stack and keeping the instruments running there is a lot going on on the PICMZ.  A USB stack would add a lot of extra work we'd need to time slice in.  We still have a lot of ideas for features we'd like to add so we wanted to make sure we were not cutting it close CPU and RAM wise.
2. Showing up as a Virtual COM device is super easy to work with and at 1.25 Mbps the COM speed was not a bottle neck.  We're currently playing around with increasing the rate to 5 Mbps but that raises some other issues with older USB ports that we need to handle.

At this point we d don't plan to add the J3 USB port back since we don't need it.  Let us know if you have more questions about this.

Thanks!

-Kristoff