Keyboard buffer

The keyboard buffer is available as an alternative to the legacy keyboard interface present on IO port $FF/255. In contrary to the legacy port it supports the full set of keys on the (USB) keyboard.

The keyboard buffer can be accessed via the KEYBUF register at IO port $FA/250. It has a 16-entry FIFO to buffer keystrokes. The FIFO can be cleared by writing any value to the IO port.

The keyboard buffer can be operated in 2 different modes: scancode mode or ASCII mode. The mode is configured via the KEYMODE command via the ESP32 interface. The keyboard buffer mode flags are as follows:

Bit	Description
0	Enable keyboard buffer
1	0:Scancode mode, 1:ASCII mode
2	Auto-repeat
3-7	Unused

When bit 0 is disabled, no new keys will be added to the keyboard buffer. Any keys still in the keyboard buffer will remain and have to be manually cleared by clearing the FIFO by writing any value to the KEYBUF register or by reading the KEYBUF register repeatedly until 0 is returned. When the auto-repeat bit is set, the pressed key is repeated after an initial delay (250ms) at 30 characters per second.

Scancode mode (not yet implemented!)

A value of 0 indicates that the key buffer is empty.

Bit 7 indicates if the key is pressed (1) or released (0). Bit 6-0 contains the scancode.

The following scancode are defined:

	x0	x1	x2	x3	x4	x5	x6	x7	x8	x9	xA	xB	xC	xD	xE	xF
0x					A	B	C	D	E	F	G	H	I	J	K	L
1x	M	N	O	P	Q	R	S	T	U	V	W	X	Y	Z	1	2
2x	3	4	5	6	7	8	9	0	Enter	Esc	Bksp	Tab	Space	-	=	[
3x	]	\	NonUS # ~	;	'	`	,	.	/	CapsLk	F1	F2	F3	F4	F5	F6
4x	F7	F8	F9	F10	F11	F12	PrScr	ScrLk	Pause	Insert	Home	PgUp	Del	End	PgDn	→
5x	←	↓	↑	NumLk	Kp/	Kp*	Kp-	Kp+	KpEnter	Kp1	Kp2	Kp3	Kp4	Kp5	Kp6	Kp7
6x	Kp8	Kp9	Kp0	Kp.	NonUS \ |	App		Kp=	F13	F14	F15	F16	F17	F18	F19	F20
7x	LCtrl	LShift	LAlt	LGui	RCtrl	RShift	RAlt	RGui

Scancodes 0x04-0x6F (4-111) are identical to the USB HID scancodes. Scancodes for the modifier keys are remapped to fit in the 7-bit scancode space.

When auto-repeat is on, only the pressed state (bit 7=1) is repeated. Modifier keys don't have auto-repeat.

ASCII mode

A value of 0 indicates that the key buffer is empty.

The following control codes are generated (ASCII 1-31):

ASCII	Ctrl-equivalent	Key
1	CTRL-A
2	CTRL-B
3	CTRL-C	Escape
4	CTRL-D
5	CTRL-E
6	CTRL-F
7	CTRL-G
8	CTRL-H	Backspace
9	CTRL-I	Tab
10	CTRL-J
11	CTRL-K
12	CTRL-L
13	CTRL-M	Enter
14	CTRL-N
15	CTRL-O
16	CTRL-P
17	CTRL-Q
18	CTRL-R
19	CTRL-S
20	CTRL-T
21	CTRL-U
22	CTRL-V
23	CTRL-W
24	CTRL-X
25	CTRL-Y
26	CTRL-Z
27	CTRL-[
28	CTRL-\
29	CTRL-]
30	CTRL-^
31	CTRL-_
127		Delete
128		Remap of character 0 (CTRL-@)