USB-USB: compatibility with ConnectPro KVM switch

[tmk]

 --------       ---       ---------      --------
|Computer|---+-|KVM|--X--|Converter|----|keyboard|
 --------    |  ---       ---------      --------
 --------    |
|Computer|---'
 -------- 

X is point where this issue happens, between converter and KVM. LUFA USB stack configuration is related.

• USB-USB converter has constant lagging, missing keystrokes and repeated key problem on the KVM 'dedicated' port.
• Realforce R2 TKL does not work at all on the KVM 'dedicated' port. It doesn't send even a single keystroke there.
• Both the Realforce and the converter works withouth problem on the KVM 'generic' port.
• GMMK TKL, Hexgears Impulse and Hexgears Nova work well on the KVM 'dedicated' port.

https://geekhack.org/index.php?topic=69169.msg3085929#msg3085929

• Dedicated port is USB port with DDM. It keeps connections with computers for devices by emulating HID devices so computers always see keyboard and mouse device there. It watches key strokes to support Hot-key.
• Generic port acts as other cheap dumb KVM switch. Devices on the port will be enumerated each time switching between computers.

Cause & Workaround

Debug console interface causes the problem. It sends debug prints every time receiving key stroke from keyboard and the KVM may not like that.

Workaround is disabling debug console.

https://geekhack.org/index.php?topic=69169.msg3086387#msg3086387

See post below.

Info

ConnectPro KVM UD-12+: https://connectpro.com/product/ud-12-plus/?v=7516fd43adaa Dynamic Device Mapping (DDM): https://connectpro.com/technology/usb-ddm/?v=7516fd43adaa

Other KVM issues: #703

[tmk]

I confirmed that the problem with UD-12+.

• USB-USB converter and Realforce RGB don't work at all on 'dedicated' port. It doesn't send even a single keystroke there. (the KVM beeps and Hot-key indicators keep blinking.)

Cause

I found that the KVM switch fails when the device has more than three USB Endpoints. USB-USB conveter has four(five) Endpoints by default and Realforce also has four.

USB-USB converter Endpoint usage:

• Keyboard 1
• Mouse 1
• Extra key 1
• Debug console 2

Mouse and Extra key share a endpoint after 5948ea0ac6 so the converter has four endpoints. Before that it had five.

Workaround

For ConnectPro KVM UD-12+ you have to limit number of endpoints upto three.

Fix

These commits reduce endpoint usage.

• Mouse and Extra key share a ep with 5948ea0ac675ca25aed84475f70366f1a8acefce
• Remove OUT ep from debug console with ed7dfa140a211bf9f36529bd33da159cda762ea4

In the result USB-USB converter uses only three ep now. f9a2e202b97ebb43373f64a8c297cd83a9cc9bc1