adb_usb: Lag on typing

[tmk]

It feels longer lag on key press.

Cause

Adding ADB mouse support causes or makes worse this problem. In addition to 12 ms polling interval
of keyboard mouse support uses another _delay_ms(12) for its polling. In the result 24ms delay is required on every keyboard polling.

tmk_keyboard/converter/adb_usb/matrix.c

Line 130 in cccd418

_delay_ms(12); // delay for preventing overload of poor ADB keyboard controller

Solution

Instead of busy loop with _delay_ms(12) it should use timer and check elapsed time.

Background

In ADB protocol host controller polls devices on bus one by one repeatedly with talk command.
https://developer.apple.com/legacy/library/technotes/hw/hw_01.html#Section2

Some old keyboards like IIgs goes bad at fast polling rate, such as missing key. You have to long interval with those keyboards, we chose 12ms.

tmk_keyboard/tmk_core/protocol/adb.c

Lines 82 to 87 in 230ed4b

	* Don't call this in a row without the delay, otherwise it makes some of poor controllers
	* overloaded and misses strokes. Recommended interval is 12ms.
	*
	* Thanks a lot, blargg!
	* <http://geekhack.org/index.php?topic=14290.msg1068919#msg1068919>
	* <http://geekhack.org/index.php?topic=14290.msg1070139#msg1070139>