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Reset on a gesture the host has no opinion about

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Control, Shift and R. It was Control, Alt and Delete, which brings up a shutdown prompt
rather than reaching the machine - and no amount of asking will change that.

IT IS A SECURE ATTENTION KEY. Every serious operating system reserves it so that it always
reaches the system and never an application, precisely so a program cannot imitate a login
screen. On Windows an application cannot see it without a kernel driver; on Linux the desktop
takes it. That is not an oversight to work around, it is the same guarantee a reset button
wants being enforced one layer further down, and there is no call this program could make
that would win the argument. It is unavailable for exactly the reason it seemed right.

So the requirement list grew a third item that was not obvious until it bit: the gesture has
to be one the host has no opinion about. Control and Shift with a letter is about as free as
a combination gets - not window management, not a virtual terminal switch, and not a shortcut
any desktop claims by default. It keeps the other two properties: plain F12 and plain Delete
stay free for software, and three keys are not pressed by accident.

If some platform does send a character for it, nothing comes of that either. Whatever arrives
is in memory that is about to be thrown away.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
This commit is contained in:
Anachronaut
2026-08-29 14:41:05 -04:00
co-authored by Claude Opus 5
parent 0afead00de
commit 8c6ed62044
2 changed files with 30 additions and 9 deletions
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Source/Emulator/voyager.c
+18 -4
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@@ -140,8 +140,22 @@ static void drainKeyboard(void) {
// memory, and a single key that does that sits one mistake away from losing work. Three keys
// together are not pressed by mistake.
//
// Control, Alt and Delete, which has meant this since 1981 and is the one gesture nobody has
// to be told the meaning of.
// Control, Shift and R. It was Control, Alt and Delete, which has meant this since 1981 and
// is the one gesture nobody has to be told the meaning of - AND WHICH CANNOT BE USED.
//
// It is a secure attention key. Every serious operating system reserves it so that it always
// reaches the system and never an application, precisely so that a program cannot imitate a
// login screen; on Windows an application cannot see it at all without a kernel driver, and
// on Linux the desktop takes it. That is not an oversight to work around - it is the same
// guarantee a reset button wants, being enforced one layer further down, and there is no
// call this program can make that would win the argument.
//
// So the gesture has to be one the host has no opinion about. Control and Shift with a
// letter is about as free as a combination gets: it is not window management, not a virtual
// terminal switch, and not a shortcut any desktop claims by default.
//
// If a platform does send a character for it, nothing comes of that either - whatever
// arrives is in memory that is about to be thrown away.
//
// What it does is what writing MACHINE_RESET does: the machine starts the way it started, so
// the boot chain runs again and finds whatever the disk now says to run. Which is what makes
@@ -152,8 +166,8 @@ static int resetPending = 0;
static void checkResetButton(void) {
const int control = IsKeyDown(KEY_LEFT_CONTROL) || IsKeyDown(KEY_RIGHT_CONTROL);
const int alt = IsKeyDown(KEY_LEFT_ALT) || IsKeyDown(KEY_RIGHT_ALT);
if (control && alt && IsKeyPressed(KEY_DELETE)) {
const int shift = IsKeyDown(KEY_LEFT_SHIFT) || IsKeyDown(KEY_RIGHT_SHIFT);
if (control && shift && IsKeyPressed(KEY_R)) {
requestReset();
// Remembered as well as asked for, so that a machine waiting on a key can be woken
// to go and notice it. See voyagerKey.