From: ol.sc <ol.sc@b7a2c559-68d2-44c3-8de9-860c34a00d81>
Date: Sat, 20 Feb 2010 09:52:05 +0000 (+0000)
Subject: Added comment based on mailing list posting by Greg King.
X-Git-Tag: V2.13.2~9
X-Git-Url: https://git.sur5r.net/?p=cc65;a=commitdiff_plain;h=9ef9396b71e9c9670e94a24d45bc89484a95e776

Added comment based on mailing list posting by Greg King.

git-svn-id: svn://svn.cc65.org/cc65/trunk@4593 b7a2c559-68d2-44c3-8de9-860c34a00d81
---

diff --git a/libsrc/c64/c64-1351.s b/libsrc/c64/c64-1351.s
index c53940d7a..d4dfa1c91 100644
--- a/libsrc/c64/c64-1351.s
+++ b/libsrc/c64/c64-1351.s
@@ -4,6 +4,24 @@
 ;
 ; 2009-09-26, Ullrich von Bassewitz
 ; 2010-02-06, Greg King
+;
+; The driver prevents the keyboard from interfering by changing the
+; keyboard's output port into an input port while the driver reads its
+; controller device.  That disables a wire that is left active by the
+; Kernal.  That wire is used by the STOP-key to break out of BASIC
+; programs -- CC65 programs don't use that feature.  The wire is shared
+; by these keys: STOP, "Q", Commodore, Space, "2", CTRL, Left-Arrow, and
+; "1".  I listed them, in order, from bit 7 over to bit 0.  The
+; rightmost five keys can look like joystick switches.
+;
+; The driver prevents the mouse/joystick from interfering by "blinding"
+; the keyboard scanner while any button/switch is active.  It changes
+; the input port into an output port, then stores all zero-bits in that
+; port's latch.  Reading from an output port sees the bitwise-AND of the
+; latch and the input signals.  Therefore, the scanner thinks that eight
+; keys are being pushed at the same time.  It doesn't know what to do
+; about that condition; so, it does nothing.  The driver lets the
+; scanner see normally, again, when no buttons/switches are active.
 ;
 
         .include        "zeropage.inc"
diff --git a/libsrc/c64/c64-joymouse.s b/libsrc/c64/c64-joymouse.s
index e99adac7a..23564c39a 100644
--- a/libsrc/c64/c64-joymouse.s
+++ b/libsrc/c64/c64-joymouse.s
@@ -3,6 +3,24 @@
 ;
 ; Ullrich von Bassewitz, 2004-03-29, 2009-09-26
 ; 2010-02-08, Greg King
+;
+; The driver prevents the keyboard from interfering by changing the
+; keyboard's output port into an input port while the driver reads its
+; controller device.  That disables a wire that is left active by the
+; Kernal.  That wire is used by the STOP-key to break out of BASIC
+; programs -- CC65 programs don't use that feature.  The wire is shared
+; by these keys: STOP, "Q", Commodore, Space, "2", CTRL, Left-Arrow, and
+; "1".  I listed them, in order, from bit 7 over to bit 0.  The
+; rightmost five keys can look like joystick switches.
+;
+; The driver prevents the mouse/joystick from interfering by "blinding"
+; the keyboard scanner while any button/switch is active.  It changes
+; the input port into an output port, then stores all zero-bits in that
+; port's latch.  Reading from an output port sees the bitwise-AND of the
+; latch and the input signals.  Therefore, the scanner thinks that eight
+; keys are being pushed at the same time.  It doesn't know what to do
+; about that condition; so, it does nothing.  The driver lets the
+; scanner see normally, again, when no buttons/switches are active.
 ;
 
         .include        "zeropage.inc"