Path: utzoo!mnetor!uunet!husc6!linus!mbunix!jcmorris
From: jcmorris@mitre-bedford.ARPA (Joseph C. Morris)
Newsgroups: comp.os.minix
Subject: Re: How do you turn on the AT's LEDs?
Message-ID: <22954@linus.UUCP>
Date: 28 Jan 88 15:09:37 GMT
References: <1832@botter.cs.vu.nl> <4240@eagle.ukc.ac.uk>
Sender: news@linus.UUCP
Reply-To: jcmorris@mbunix (Morris)
Organization: The MITRE Corporation, McLean, VA.
Lines: 56
Summary: Try it.

In article <1836@botter.cs.vu.nl> ast@cs.vu.nl (Andy Tanenbaum) writes:
>As everyone with MINIX on an AT has observed, hitting caps lock does not turn
>on the LED.

(Another response to Andy's message):

This is a pseudo-code summary of the LED code in the original AT.  As
usual, no guarantees, and your mileage may vary.  (This code doesn't
exactly match the executive summary I recently posted.  It's amazing 
how much detail one can find in a program when you read it carefully...8-)=

write_led(bits):
        IF led_update_in_progress THEN EXIT
        SET led_update_in_progress
        DISMISS_INTERRUPT                       [send EOI to port 020h]
        CALL kb_send (LED_CMD)                  [LED_CMD = 007h]
        IF send_err GOTO sl2
        CALL kb_send (bits)                     [low three bits set 3 LED's]
        IF send_err GOTO sl3
sl2:    CALL kb_send (KB_ENABLE)                [KB_ENABLE = 0f4h]
sl3:    RESET led_update_in_progress
	RESET send_err
        EXIT

kb_send(byte):
sd0:    RESET kb_fa
        RESET kb_fe
sd5:    IN KB_STATUS                            [KB_STATUS = port 064h]
        IF inpt_buf_full THEN GOTO sd5          [inpt_buf_full = 002h]
        OUT PORT_A,byte                         [PORT_A = port 060h]
sd1:    IF (kb_fa or kb_fe) THEN GOTO sd3
        IF NOT 01a00_times_here THEN GOTO sd1   [approx. 10 msec]
sd2:    IF NOT 3rd_time_here THEN GOTO sd0      [retry limit]
        SET send_err
        EXIT
sd3:    IF kb_fa THEN EXIT                      [if keyboard acknowledge]
        GOTO sd2                                [must be resend order]

[part of keyboard interrupt follows:]
        ...                                     [scan code has been read
        ...                                      from keyboard]
        IF SCAN EQ kb_ack THEN                  [kb_ack =  0fah]
                {                               [keyboard acknowledge]
                SET kb_fa
                GOTO kb_exit                    [exit from keyboard interrupt]
                }
        IF SCAN EQ kb_resend THEN               [kb_resend = 0feh]
                {                               [keyboard requests resend]
                SET kb_fe
                GOTO kb_exit
                }
        ...

Hope this helps...

/Joe Morris