Fixed: ADB-USB converter misses keystrokes

[tmk]

2013/11/15

The problem is very complicated and comprised of various possible causes.

missing ADB singnal with interrupts by USB

During handle ADB signal the code have to be guraded from USB or other interrupts with cli(). Both receive and send signal codes needs this gurad in adb.c.
http://geekhack.org/index.php?topic=14290.msg1118206#msg1118206

mis-handle of two key events in an ADB transaction

Both of down and up event of a key can be sent with same one 16-bit ADB packet.

• http://geekhack.org/index.php?topic=14290.msg1114073#msg1114073

preventing keyboard from scaning matrix with high rate of ADB polling

If converter polls too frequently keyboard has to consume lots of controller cycles to respond to the requests and could miss change of key switch in the result. Older keyboard tends to suffer from this severely. 12ms is proper interval.
http://geekhack.org/index.php?topic=14290.msg1118206#msg1118206

Original description

This was not accurate at all:

At commit:38effe4ae4a691dcf034c31f67d1bdb2156ba7f5 the converter has this problem,
while old commit:33d58c2b5647623d2b07a210ef97a27920e5563e doesn't have it.

[tmk]

AppleIIGS keyboard and M0116 suffer severely from this issue, while Extended keyboards M0115 and M3501 doesn't seem like so bad. Though it may depend on type speed. In my speed 50-60wpm with Extended keyboard I don't feel big problem.

Some ADB keyboards seem to have little key buffers so I guess we'll need to poll the keyboards much faster.

[tmk]

After stop bit of talk command it waits for start bit of data longer(255 to 500us) now.

@@ -88,19 +89,24 @@ uint16_t adb_host_kbd_recv(void)
     attention();
     send_byte(0x2C);            // Addr:Keyboard(0010), Cmd:Talk(11), Register0(00)
     place_bit0();               // Stopbit(0)
-    if (!wait_data_lo(0xFF))    // Tlt/Stop to Start(140-260us)
+    if (!wait_data_lo(500)) {   // Tlt/Stop to Start(140-260us)
         return 0;               // No data to send

[tmk]

IIgs and M0116 keyboards still sometime drop key stroke when pressing same key successively.
Not sure this is bug but firmware is not perfect in fact and could still have some bugs.

http://geekhack.org/index.php?topic=14290.msg1064533#msg1064533

This problem is not so severe than it used to be before the fix. To me it seems to be almost no problem for normal typing. My typing wpm is around 60.

[tmk]

Still key drop is thre. It must be bug. Looks like code is need to be rewritten from scratch completely
and check signal with scope to conform to the spec.

http://geekhack.org/index.php?topic=14290.msg1064567#msg1064567

[tmk]

With interval between scans it seems the problem is gone or mitigated dramatically.

http://geekhack.org/index.php?topic=14290.msg1068919#msg1068919

[tmk]

ADB scan rates of old Mac'. 12ms seems to be safe.
http://geekhack.org/index.php?topic=14290.msg1070139#msg1070139

[tmk]

Fixed with this commit: c18c52f

Plz report if you still suffer from this.

[tmk]

Finally fixed at d2a83da

http://geekhack.org/index.php?topic=14290.msg1134847#msg1134847

Thank you gblargg!