Hi, Brennan,
I am inclined to stick with the FT245RL because the boards are cheap and
readily available. Conceptually, the basic solution does not depend on
the selection of hardware. The hardware does effect performance and
scalability, but I think the that the hardware selection is not critical
for initial development.
I can get the RT245RL board for ~$11 USD on eBay an adequate
STM32F103/F407 for $10-15 from China. Ready availability, inexpensive
hardware (albeit low performance) would probably be a better starting
point.. unless you can point to a competing low cost OTS solution. The
combined cost is around $20 and meets all of the initial development
requirements. I would have to have to have strong reason to deviate
from that. But I could be very easily dissuaded with an alternative OTS
hardware proposal at similar cost.
Nothing I have said precludes that alternative, higher performance
implementation. At a block diagram level, it does not matter. It is
just a matter of drivers on both sides.
Greg
On 6/12/2020 6:27 PM, Brennan Ashton wrote:
On Fri, Jun 12, 2020, 5:18 PM Gregory Nutt <spudan...@gmail.com> wrote:
Hi, again,
I suppose the first question should be, "Is the FT245RL the correct
choice?" After all, it is only 8-bits wide and only USB 2.0. That could
limit the amount of instrumentation data passed to the host because of data
overrun or or it could alter the real-time behavior of the target.
Ideally, the instrumentation should involve minimal overhead and the
behavior the real time system should be the same with or without the
instrumentation enabled. Otherwise, such a tool would not be a proper
diagnostic tool.
I considered some PCIe parallel data acquisition devices, but did not see
a good match. PCIe would be hot, howeer.
I also looked at FTDI FT60xx devices, but these seem so camera focused
that it was not completely clear to me that these could be usable. But I
am a mostly a software guy. Perhaps someone out there with better
knowledge of these devices could help out.
The older FT600x, for example, has a 16-bits wide FIFO (pretty much
optimal for most MCUs) and has a USB 3.0 interface to the host PC. Using
such a camera-oriented device is less obvious to me than the more general
FT245RL. Perhaps that is only because of the camera-oriented language used
in the data sheets?
If you know something about these options, I would like to hear from you.
Greg
If you want high-speed io to USB the FX3 is probably one of the best bets.
You see it frequently used on logic analyser and software defined radio
boards between the USB and the FPGA.
https://www.cypress.com/products/ez-usb-fx3-superspeed-usb-30-peripheral-controller
Somewhat related but have in the past modified the firmware on this for
some custom debugging. https://1bitsquared.com/products/black-magic-probe
--Brennan
