Use a single endpoint for HID reports (#3951)

* Unify multiple HID interfaces into one

This reduces the number of USB endpoints required, which frees them up
for other things.

NKRO and EXTRAKEY always use the shared endpoint.

By default, MOUSEKEY also uses it. This means it won't work as a Boot
Procotol mouse in some BIOSes, etc. If you really think your
keyboard needs to work as a mouse in your BIOS, set
MOUSE_SHARED_EP = no in your rules.mk.

By default, the core keyboard does not use the shared endpoint, as not
all BIOSes are standards compliant and that's one place you don't want
to find out your keyboard doesn't work.. If you are really confident,
you can set KEYBOARD_SHARED_EP = yes to use the shared endpoint here
too.

* unify endpoints: ChibiOS protocol implementation

* fixup: missing #ifdef EXTRAKEY_ENABLEs

broke build on AVR with EXTRAKEY disabled

* endpoints: restore error when too many endpoints required

* lufa: wait up to 10ms to send keyboard input

This avoids packets being dropped when two reports are sent in quick
succession (eg. releasing a dual role key).

* endpoints: fix compile on ARM_ATSAM

* endpoint: ARM_ATSAM fixes

No longer use wrong or unexpected endpoint IDs

* endpoints: accommodate VUSB protocol

V-USB has its own, understandably simple ideas about the report formats.
It already blasts the mouse and extrakeys through one endpoint with
report IDs. We just stay out of its way.

* endpoints: document new endpoint configuration options

* endpoints: respect keyboard_report->mods in NKRO

The caller(s) of host_keyboard_send expect to be able to just drop
modifiers in the mods field and not worry about whether NKRO is in use.
This is a good thing. So we just shift it over if needs be.

* endpoints: report.c: update for new keyboard_report format

1 files changed, 29 insertions, 0 deletions

diff --git a/docs/config_options.md b/docs/config_options.md
index c4921c21d..b811fa877 100644
--- a/docs/config_options.md
+++ b/docs/config_options.md
@@ -261,3 +261,32 @@ Use these to enable or disable building certain features. The more you have enab
   * Forces the keyboard to wait for a USB connection to be established before it starts up
 * `NO_USB_STARTUP_CHECK`
   * Disables usb suspend check after keyboard startup. Usually the keyboard waits for the host to wake it up before any tasks are performed. This is useful for split keyboards as one half will not get a wakeup call but must send commands to the master.
+
+## USB Endpoint Limitations
+
+In order to provide services over USB, QMK has to use USB endpoints.
+These are a finite resource: each microcontroller has only a certain number.
+This limits what features can be enabled together.
+If the available endpoints are exceeded, a build error is thrown.
+
+The following features can require separate endpoints:
+
+* `MOUSEKEY_ENABLE`
+* `EXTRAKEY_ENABLE`
+* `CONSOLE_ENABLE`
+* `NKRO_ENABLE`
+* `MIDI_ENABLE`
+* `RAW_ENABLE`
+* `VIRTSER_ENABLE`
+
+In order to improve utilisation of the endpoints, the HID features can be combined to use a single endpoint.
+By default, `MOUSEKEY`, `EXTRAKEY`, and `NKRO` are combined into a single endpoint.
+
+The base keyboard functionality can also be combined into the endpoint,
+by setting `KEYBOARD_SHARED_EP = yes`.
+This frees up one more endpoint,
+but it can prevent the keyboard working in some BIOSes,
+as they do not implement Boot Keyboard protocol switching.
+
+Combining the mouse also breaks Boot Mouse compatibility.
+The mouse can be uncombined by setting `MOUSE_SHARED_EP = no` if this functionality is required.