How to add extra SerialUSB to Teensy4.1

[andystephenson]

Hi,

I have tried expanding on TRIPLE SERIAL in the hope of creating HEPTA_SERIAL, which will give me Serial, plus SerialUSB1..6.

I have editied and created in some cases:

yield.cpp
serialEventUSB3.cpp
serialEventUSB4.cpp
serialEventUSB5.cpp
serialEventUSB6.cpp
core_pins.h
usb.c
usb_serial.h
usb_inst.cpp
usb_desc.h
usb_desc.c
EventResponder.cpp
usb_serial4.cpp
usb_serial5.cpp
usb_serial6.cpp
usb_serial7.cpp

boards.txt
keywords.txt

There is a lot of stuff here, so I don't want to blindly post it.

It all compiles, but only SerialUSB1 works, the others do not. If I specify TRIPLE_SERIAL, then SerialUSB1 and 2 are OK. Just my implementation breaks things. I do get all of the ports enumerating on both a rasp pi, and a mac, just no data passes through. My simple test just sends a string every second to the SerialUSBn ports.

So first off, is what I am attempting OK?

If I'm on the right track, have I missed a file in the edits?

I can of course post all of my files if it's not really obvious where my issue lies.

Thanks,

Andy

[KurtE]

Sorry, this is probably a question that maybe only Paul can answer,

But my gut tells me that you may not be able to do this.
That is the IMXRT1060RM section 42.2.1 mentions: Up to 8 bidirectional endpoints per each of the two USB controllers.

And I believe each USB Serial requires 2 end points and there is 1 extra one used. Not sure if one could disable that other end point.
But if you look for example at the Triple Serial:
It is using up to ENDPOINT7...

So again I could be wrong, and maybe one could fudge a 4th Serial... But I don't think you could go beyond that.

[andystephenson]

Sorry, this is probably a question that maybe only Paul can answer,

But my gut tells me that you may not be able to do this.
That is the IMXRT1060RM section 42.2.1 mentions: Up to 8 bidirectional endpoints per each of the two USB controllers.

And I believe each USB Serial requires 2 end points and there is 1 extra one used. Not sure if one could disable that other end point.
But if you look for example at the Triple Serial:
It is using up to ENDPOINT7...

So again I could be wrong, and maybe one could fudge a 4th Serial... But I don't think you could go beyond that.

Oh bugger. Looks like I need to come up with another plan. Lets see what Paul can add. Thanks.

[PaulStoffregen]

Kurt is right. The Teensy 4.x hardware simply does not support enough endpoints to add a 4th CDC serial.

But it could be done on Teensy 3.x. Each CDC serial needs 2 endpoints (1 bidirectional data, 1 unidirectional status). The USB device hardware on Teensy 3.x can implement up to 16 endpoints and only endpoint 0 is reserved.

[MichaelMeissner]

Well one off the wall thought is to add a UART to USB converter and use one of the hardware serial ports. In theory, something like:

• https://www.amazon.com/CP2102-Module...T93/ref=sr_1_1
• https://www.amazon.com/HiLetgo-CP210.../dp/B00LODGRV8

Note, I haven't used these boards. The low end boards don't have flow control options.

[andystephenson]

Kurt is right. The Teensy 4.x hardware simply does not support enough endpoints to add a 4th CDC serial.

But it could be done on Teensy 3.x. Each CDC serial needs 2 endpoints (1 bidirectional data, 1 unidirectional status). The USB device hardware on Teensy 3.x can implement up to 16 endpoints and only endpoint 0 is reserved.

Thanks Paul. Since it's clear my initial plan won't work, I can look at alternatives. Combining the 4 serial port data streams on the USB host and using one SerialUSB on the teensy and demuxing them is an option.

Thanks again.

...Andy

[andystephenson]

Well one off the wall thought is to add a UART to USB converter and use one of the hardware serial ports. In theory, something like:

• https://www.amazon.com/CP2102-Module...T93/ref=sr_1_1
• https://www.amazon.com/HiLetgo-CP210.../dp/B00LODGRV8

Note, I haven't used these boards. The low end boards don't have flow control options.

Thanks for the suggestion, but in this case I only have on e USB port and don't want to add a hub into the design. The data is packeted, so I can implement a mux/demux to combine the data into one USB stream.

Thanks.