Controllers: four pads that say what is held

The console says WHICH KEY WENT DOWN, which is the right shape for typing
and the wrong one for playing. A game wants to know what is being held,
this frame, possibly several things at once, and a stream of presses
cannot say that: a key that is down and staying down sends nothing at all.
Lunar Porter's thrust is a burn per press for exactly that reason.

So a pad is its own device on ports 0x60 to 0x6F, reporting a LEVEL. One
read gives every button at once, holding is the natural thing to express,
two directions together cost nothing, and reading does not consume it - a
game may ask twice in a frame and be told the same thing both times.

Four of them, because a party is four. They cost a port each and nothing
at all when unused. The directions are the low nibble so "which way" is an
AND with 0x0F; the buttons are the high nibble for the same reason. 0x64
says which are really there, so a game can ask for a controller rather
than sitting silent while somebody presses things at it. They never
interrupt: a game polls once a frame because that is when it draws.

KEY-UP ON THE CONSOLE WAS THE OTHER WAY TO DO THIS AND WAS REJECTED. A
terminal hands over characters and can never report a key coming up
however it is asked, so it would have been a thing that worked behind a
window and silently did not down a wire. A separate device can honestly
say it is not there.

Voyager drives pad nought from the keyboard as well as from any real
controller, OR-ed rather than chosen between, so a game written for a pad
is playable on a machine with none and unplugging one mid-game does not
leave somebody holding nothing.

And a recorded path, which is what makes any of it testable: --pad names a
file of one byte a frame, and the manifest has an eighth column for it.
A BYTE A FRAME AND NOT A BYTE A READ - a level asked twice in one frame
has to answer the same both times, and a file that advanced per read would
depend on how the program happened to be written. Voyager's own tests run
headless with nobody holding anything, so without this the device would be
exercised only by somebody playing: the state the console's line editing
was in when it broke twice in two days.

0x50 is the timer, not free. The block this went in was chosen after
looking rather than before.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW

Source/Emulator/io.c

@@ -7,6 +7,7 @@
 #include "../Assembler/assembly.h" // For the fault vector numbers.
 #include "controller.h"
 #include "video.h"
+#include "pad.h"
 #include "sound.h"
 #include "font.h"
 #include <stdio.h>
@@ -1168,6 +1169,9 @@ void deviceTick(unsigned long now) {
     soundTick(now);
     // And the timer, which is the only beat a program can choose for itself.
     timerTick(now);
+    // And the pads, whose recordings step on a frame so that a level read twice in one is
+    // the same level both times.
+    padTick(now);
     if (diskPending && now >= diskReadyAt) {
         diskSettle();
     }
@@ -1341,6 +1345,7 @@ static const DeviceRecord deviceTable[] = {
     { PORT_VIDEO,    DEVICE_VIDEO,    DEVICE_FLAG_HAS_MEMORY },
     { PORT_SOUND,    DEVICE_SOUND,    0 },
     { PORT_TIMER,    DEVICE_TIMER,    0 },
+    { PORT_PAD,      DEVICE_PAD,      0 },
     { PORT_REGISTRY, DEVICE_REGISTRY, 0 },
 };
 static const int deviceCount = (int)(sizeof(deviceTable) / sizeof(deviceTable[0]));
@@ -1393,6 +1398,11 @@ static const DeviceRecord *deviceOnPort(uint8_t port) {
     if (port > PORT_TIMER && port <= PORT_TIMER_TOP) {
         return deviceOnPort(PORT_TIMER);
     }
+    // Sixteen ports, one device: four pads, a port saying which are there, and eleven kept
+    // for the analogue axes that are not built.
+    if (port > PORT_PAD && port <= PORT_PAD_TOP) {
+        return deviceOnPort(PORT_PAD);
+    }
     for (int i = 0; i < deviceCount; i++) {
         if (deviceTable[i].port == port) {
             return &deviceTable[i];
@@ -1570,6 +1580,9 @@ uint8_t InputHandler(uint8_t Address) {
     if (Address >= PORT_SOUND && Address <= PORT_SOUND_TOP) {
         return soundRead(Address);
     }
+    if (Address >= PORT_PAD && Address <= PORT_PAD_TOP) {
+        return padRead(Address);
+    }
     if (Address >= PORT_TIMER && Address <= PORT_TIMER_TOP) {
         return timerRead(Address);
     }