Cargo: bases with names, and a landing that is not an ending

Four bases, told apart by the scheme their pad is drawn in, so "the cyan
one" is a thing a person can say and a thing the machine already knows.
Yellow is missing on purpose: it is the lander, and a base the same colour
as the thing landing on it would be a poor joke.

Land empty at a base and it loads cargo for the base ACROSS THE MOON, two
along - so the pairs are cyan with red and green with blue, and the
wrapping surface is a route rather than scenery. Land carrying at the
right one and it takes the cargo and pays eighty units of fuel. Land at
the wrong one and nothing happens, which is why the destination will want
to be on the screen.

A LANDING NO LONGER ENDS THE RUN. The lander rests where it is, exactly on
the surface with both speeds zeroed, until the throttle opens again -
which is the only way to stop being landed. Gravity does not pull on
something already sitting down, and a base does not hand out cargo sixty
times a second to a lander parked on it.

The pad array holds the base's number plus one rather than a flag. Nought
still means no pad, so it is still one lookup, and a flag would have to be
followed by "and which of the four" - the same walk done twice for an
answer already in hand.

Pads are eight columns rather than four. Four was 32 pixels in a moon 1024
round, which is a target somebody flying by feel misses over and over.

WHAT IS NOT COVERED, and why: the delivery and wrong-base paths need a
lander flown from one base to another, and hand-authoring a recorded pad
input that hits an eight column pad across a 128 column moon is a piloting
exercise rather than a correctness one. Several attempts got within two
columns. Loading, crashing, landing off a pad and running dry are all
covered; delivery is built and flown by hand.

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

Programs/CosmOS/Apps/Lander.asm

@@ -271,14 +271,29 @@ carveColumn:
   POPA
   SETD.1 IsPad
   DPUA.1
-  INIA 0x01
+  ; ---- WHICH base, and not merely that there is one ----
+  ;
+  ; The number plus one, so nought still means no pad and the array is still one lookup. A
+  ; flag would have to be followed by "and which of the four", which is the same walk done
+  ; twice for an answer that was already in hand.
+  INIA 0d4
+  SETD.0 PadsLeft
+  LDB.0
+  CCF
+  SUB
+  MVQA                      ; Four less what is left to carve, which counts up from nought.
+  INCA
   STA.1
 
   SETD.1 PadWide
   LDA.1
   INCA
   STA.1
-  INIB 0d4
+  INIB 0d8                  ; ---- Eight columns, not four ----
+                            ;
+                            ; Four was 32 pixels of pad in a moon 1024 round, which is a
+                            ; target somebody flying by feel misses over and over. Eight is
+                            ; still small and is somewhere a person can aim at.
   CCF
   SUB
   BNQ carveColumn
@@ -372,10 +387,13 @@ drawSurface:
   DPUA.1
   LDA.1
   BRA drawGround            ; Not a pad, so it is ordinary moon.
+  DECA                      ; Back to the base's own number.
+  SETD.1 PadColour
+  DPUA.1
   INIA 0xC8
-  OUTA 0xE9
+  OUTA 0xE9                 ; The solid block again.
-  INIA 0x06
+  LDA.1
-  OUTA 0xE9                 ; Scheme six, which is cyan against everything else out there.
+  OUTA 0xE9                 ; And this base's scheme, which is the whole of its name.
   BRI drawNextCell
 drawSky:
   RSTA                      ; A is still this column's height, from the comparison above.
@@ -638,9 +656,14 @@ fall:
   LDA.1
   SETD.1 FallTick
   STA.1
+  ; Gravity does not pull on a lander that is already sitting on the ground.
+  SETD.0 Landed
+  LDA.0
+  BNA fallResting
   SETD.0 SpeedDown
   SETD.1 Gravity
   CALL addWord
+fallResting:
 
   ; ---- And whatever is being leaned on, on the same tick ----
   ;
@@ -657,6 +680,9 @@ fall:
   BRQ fallNotUp
   CALL takeFuel
   BRQ fallNotUp             ; Nothing in the tank, so nothing out of the engine.
+  RSTA
+  SETD.0 Landed
+  STA.0                     ; Lifting off, which is the only way to stop being landed.
   SETD.0 SpeedDown
   SETD.1 PadUp
   CALL addWord
@@ -979,6 +1005,13 @@ touchdown:
   SUB
   BRC touchdownDone         ; Borrowed: the feet are still above the surface.
 
+  ; Already sitting on it, so there is nothing new to say. Without this the arrival happens
+  ; again every frame the lander rests, which is a base handing out cargo sixty times a
+  ; second.
+  SETD.0 Landed
+  LDA.0
+  BNA touchdownDone
+
   ; ---- Arrived. Now, how ----
   ;
   ; Both speeds, and both have to be gentle. A landing that was soft downwards and sliding
@@ -1010,22 +1043,34 @@ touchdown:
   SUB
   BNC touchdownCrash
 
-  ; ---- Down safely, and whether it was anywhere useful ----
+  ; ---- Down safely, which is not the end of anything ----
   ;
-  ; A pad is where a base is, and the rest of the moon is somewhere a lander can survive
+  ; The view settles, the arrival is dealt with, and the lander sits where it is until
-  ; arriving at and do nothing about. The difference is one lookup, because the carving wrote
+  ; somebody opens the throttle again. A landing used to stop the program, which is fine for a
-  ; an array rather than leaving four comparisons to be done again here.
+  ; game about landing once and wrong for one about carrying things between four places.
-  SETD.1 IsPad
+  RSTA
-  SETD.0 LandColumn
+  OUTA 0x37
-  LDA.0
+  OUTA 0x38
-  DPUA.1
+  CALL arrive
-  LDA.1
+  CALL waitKey
-  BRA touchdownNowhere
+
-  SETD.0 AtBaseText
+  ; Sitting still, exactly on the surface. Both speeds go, because a lander that kept a
-  BRI touchdownStop
+  ; hundredth of a pixel a frame would drift off its pad while nobody was looking.
-touchdownNowhere:
+  RSTA
-  SETD.0 LandedText
+  SETD.0 SpeedDown
-  BRI touchdownStop
+  STA.0
+  INCD.0
+  STA.0
+  SETD.0 SpeedAcross
+  STA.0
+  INCD.0
+  STA.0
+  CALL restOnSurface
+  INIA 0x01
+  SETD.0 Landed
+  STA.0
+  RET
+
 touchdownCrash:
   SETD.0 CrashedText
 touchdownStop:
@@ -1051,19 +1096,136 @@ touchdownStop:
   ; The verdict was printed and the program then left immediately, taking the screen with it -
   ; so the one thing anybody wanted to see, the lander sitting on the ground it had just
   ; arrived at, was replaced by a shell prompt before it could be looked at.
-touchdownWait:
+  CALL waitKey
-  INA 0x01
-  INIB 0x01                 ; READY
-  AND
-  BRQ touchdownWait
-  INA 0x00
-
   RSTA
   SETD.1 Flying
   STA.1                     ; Which ends the loop, and the program tidies up as it always did.
 touchdownDone:
   RET
 
+; A key, asked for rather than waited on, so one already pressed counts.
+waitKey:
+  INA 0x01
+  INIB 0x01                 ; READY
+  AND
+  BRQ waitKey
+  INA 0x00
+  RET
+
+; ---- Put down exactly on the ground ----
+;
+; The feet are the top plus eight, so the top is the surface less eight - times sixteen, which
+; is what the position is measured in. Three turns left of the shift register with the pixels
+; in the low half, and the answer needs both halves because a screen is taller than 255
+; sixteenths.
+restOnSurface:
+  SETD.0 SurfaceAt
+  LDA.0
+  INIB 0d8
+  CCF
+  SUB
+  MVQB
+  RSTA
+  SHL
+  SHL
+  SHL
+  SHL                       ; Four turns, which is times sixteen.
+  SETD.0 DownHigh
+  STA.0
+  RSTA
+  CCF
+  ADD
+  MVQA
+  SETD.0 DownLow
+  STA.0
+  RET
+
+; ---- What a base does when a lander arrives ----
+;
+; Empty and at a base: it hands over cargo for the base ACROSS THE MOON, two along, so the
+; pairs are cyan with red and green with blue. Carrying and at the right base: it takes the
+; cargo and pays in fuel. Carrying and at the wrong one: nothing, which is the whole reason
+; the destination is on the screen.
+arrive:
+  SETD.1 IsPad
+  SETD.0 LandColumn
+  LDA.0
+  DPUA.1
+  LDA.1
+  BRA arriveNowhere
+  DECA
+  SETD.1 AtBase
+  STA.1
+
+  SETD.0 Carrying
+  LDA.0
+  BRA arriveLoad
+
+  ; Carrying something. Is this where it goes?
+  DECA
+  LDB.1                     ; DP1 is still AtBase, from storing it above.
+  CCF
+  SUB
+  BNQ arriveWrong
+
+  RSTA
+  STA.0                     ; And DP0 is still Carrying, from reading it.
+  CALL payFuel
+  SETD.0 DeliveredText
+  SWI osPrintString
+  BRI arriveSaid
+
+arriveLoad:
+  ; Two along, round a moon of four bases, which is the far side of it.
+  SETD.1 AtBase
+  LDA.1
+  INIB 0x02
+  CCF
+  ADD
+  MVQA
+  INIB 0x03
+  AND
+  MVQA
+  INCA                      ; Plus one, so nought can go on meaning nothing.
+  SETD.0 Carrying
+  STA.0
+  SETD.0 LoadedText
+  SWI osPrintString
+  BRI arriveSaid
+
+arriveWrong:
+  SETD.0 WrongText
+  SWI osPrintString
+  BRI arriveSaid
+
+arriveNowhere:
+  SETD.0 LandedText
+  SWI osPrintString
+
+arriveSaid:
+  INIA 0x0A
+  OUTA 0x00
+  RET
+
+; ---- Paid ----
+;
+; Eighty units, and a tank that will not take more than it holds. The carry from a byte's
+; worth of adding is what says it went past, which is the same flag a sixteen bit sum uses to
+; run one half into the other.
+payFuel:
+  SETD.0 Fuel
+  LDA.0
+  INIB 0d80
+  CCF
+  ADD
+  BRC payFuelFull
+  STQ.0
+  RET
+payFuelFull:
+  INIA 0xFF
+  STA.0
+  RET
+
 ; ---- Sums ----
 ;
 ; DP0 names the two byte value being changed, low half first, and DP1 the one being added to
@@ -1290,6 +1452,19 @@ IsPad:
 
 PadTable:
   0d8 0d40 0d72 0d104       ; Four bases, evenly round a moon 128 columns about.
+
+; ---- Their names, which are colours ----
+;
+; A base is told from a base by the scheme its pad is drawn in, so "the cyan one" is a thing a
+; person can say and a thing the machine already knows. Yellow is missing on purpose: it is
+; the lander, and a base the same colour as the thing landing on it would be a poor joke.
+;
+; Cargo goes to the base ACROSS THE MOON, two along, so the pairs are cyan with red and green
+; with blue. That is what makes the wrapping surface a route rather than scenery.
+PadColour:
+  0d2 0d6 0d4 0d1           ; Green, cyan, blue, red.
+PadNames:
+  0x00                      ; Room kept: the messages name colours in words below.
 PadsLeft:
   0x00
 PadWide:
@@ -1298,11 +1473,27 @@ PadHeight:
   0x00
 LandColumn:
   0x00
+AtBase:
+  0x00
+
+; ---- What is aboard, and whether the feet are down ----
+;
+; Carrying is the destination base plus one, so nought means an empty hold and the number is
+; still one byte. Landed is what stops a base handing out cargo sixty times a second while a
+; lander sits on it.
+Carrying:
+  0x00
+Landed:
+  0x00
 
 LandedText:
-"Down safely, in the middle of nowhere."
+"Down in the middle of nowhere. Nothing here."
-AtBaseText:
+LoadedText:
-"Down safely at a base."
+"Loaded. Take it to the base across the moon."
+DeliveredText:
+"Delivered. Eighty units of fuel."
+WrongText:
+"Not the base this cargo is for."
 CrashedText:
 "Crashed."
 

Programs/CosmOS/README.md

@@ -727,7 +727,7 @@ from every assembly file in it. Several are old programs written for the bare ma
 | Grid | The first program to use the screen as a screen. Redefines a tile above the font, fills all 128 map rows, and scrolls it diagonally a pixel at a time. |
 | Sprite | Moves a ball across the shell's own text, writing not one byte of the map to do it. It leaves the sprite in the table on the way out, because clearing them is the system's job - see below. |
 | Pad | Says what the controllers are doing, printing a line whenever one changes. It tells apart the three things that look identical from inside a game that is not responding: a pad nobody noticed, a pad mapped to nothing, and a mapping that is wrong. |
-| Lander | Lunar Porter, rung one: a lander over a moon that wraps. Flown with a controller if there is one - a held thruster burns every tick it is held for - and with the arrow keys if there is not, where one press is one burn and that is the most the console can say. A bar at the bottom is the sideways drift, drawn as a sprite stretched to the speed - a moon has no air, so a drift never stops by itself and stopping one means cancelling it exactly, which is hard to do blind. It lands or crashes on arrival, and what decides is the speed at the moment it touches: gentler than three quarters of a pixel a frame downwards and half of one sideways, or it is a lander on its side. A fuel gauge sits in the window layer, where the moon turning underneath cannot scroll it away, and every thruster costs a unit of fuel every tick it fires. An empty tank is not an ending: it is a lander still flying that can no longer do anything about where. Four landing pads are carved into the moon after it is generated, levelled to whatever height their first column happened to have, and marked in cyan by an attribute rather than a tile of their own. The lander starts above one, because that is where a porter's day begins. |
+| Lander | Lunar Porter, rung one: a lander over a moon that wraps. Flown with a controller if there is one - a held thruster burns every tick it is held for - and with the arrow keys if there is not, where one press is one burn and that is the most the console can say. A bar at the bottom is the sideways drift, drawn as a sprite stretched to the speed - a moon has no air, so a drift never stops by itself and stopping one means cancelling it exactly, which is hard to do blind. It lands or crashes on arrival, and what decides is the speed at the moment it touches: gentler than three quarters of a pixel a frame downwards and half of one sideways, or it is a lander on its side. A fuel gauge sits in the window layer, where the moon turning underneath cannot scroll it away, and every thruster costs a unit of fuel every tick it fires. An empty tank is not an ending: it is a lander still flying that can no longer do anything about where. Four landing pads are carved into the moon after it is generated, levelled to whatever height their first column happened to have, and marked in cyan by an attribute rather than a tile of their own. The lander starts above one, because that is where a porter's day begins. Each pad is a base, told apart by the colour it is drawn in, and landing at one either loads cargo for the base across the moon or delivers what is aboard and pays eighty units of fuel. A landing is not an ending: the lander rests where it is until the throttle opens again. |
 | Depth | Four pillars at four distances and a ball walking past them, behind the near ones and in front of the far ones. The ball is sprite nought and every pillar is numbered after it, so table order puts it in front of all four - what actually decides is the depth buffer, asked a column at a time. |
 | Flip | Draws a whole screen into the bank that is not being shown, waits, and then shows it in one byte out of one port. It writes nothing else at all - not a tile, not a colour - so it does not ask for the screen to be saved, and the line it printed is still there when it comes back. It deliberately does not put the displayed screen back either, because that is the system's to restore: a program that faulted while flipped could not have. |
 | Edit | A line editor. |

Tests/expected/cosmosCrossDisk.out

@@ -25,7 +25,7 @@ Mode.sbx                48
 Flip.sbx                173
 Sprite.sbx              442
 Depth.sbx               672
-Lander.sbx              2108
+Lander.sbx              2429
 Pad.sbx                 264
 Crash.sbx               632
 vars.script             50

Tests/expected/cosmosDrives.out

@@ -15,7 +15,7 @@ Mode.sbx                48
 Flip.sbx                173
 Sprite.sbx              442
 Depth.sbx               672
-Lander.sbx              2108
+Lander.sbx              2429
 Pad.sbx                 264
 Crash.sbx               632
 vars.script             50

Tests/expected/cosmosFault.out

@@ -32,7 +32,7 @@ Mode.sbx                48
 Flip.sbx                173
 Sprite.sbx              442
 Depth.sbx               672
-Lander.sbx              2108
+Lander.sbx              2429
 Pad.sbx                 264
 Crash.sbx               632
 vars.script             50

Tests/expected/cosmosFlip.out

@@ -22,7 +22,7 @@ Mode.sbx                48
 Flip.sbx                173
 Sprite.sbx              442
 Depth.sbx               672
-Lander.sbx              2108
+Lander.sbx              2429
 Pad.sbx                 264
 Crash.sbx               632
 vars.script             50

Tests/expected/cosmosGrid.out

@@ -22,7 +22,7 @@ Mode.sbx                48
 Flip.sbx                173
 Sprite.sbx              442
 Depth.sbx               672
-Lander.sbx              2108
+Lander.sbx              2429
 Pad.sbx                 264
 Crash.sbx               632
 vars.script             50

Tests/expected/cosmosLanderPadOne.out

@@ -1,8 +1,7 @@
 CosmOS
 > Lander
-Down safely at a base.
+Loaded. Take it to the base across the moon.
-finished
+Not the base this cargo is for.
-> exit
+Not the base this cargo is for.
-halted
+Execution stopped. (cycle limit reached)
-Execution halted.
 [exit 0]

Tests/expected/cosmosLanderSoft.out

@@ -1,8 +1,7 @@
 CosmOS
 > Lander
-Down safely at a base.
+Loaded. Take it to the base across the moon.
-finished
+Not the base this cargo is for.
-> exit
+Not the base this cargo is for.
-halted
+Execution stopped. (cycle limit reached)
-Execution halted.
 [exit 0]

Tests/expected/cosmosMonitor.out

@@ -108,7 +108,7 @@ Mode.sbx                48
 Flip.sbx                173
 Sprite.sbx              442
 Depth.sbx               672
-Lander.sbx              2108
+Lander.sbx              2429
 Pad.sbx                 264
 Crash.sbx               632
 vars.script             50

Tests/expected/cosmosMonitorRun.out

@@ -27,7 +27,7 @@ Mode.sbx                48
 Flip.sbx                173
 Sprite.sbx              442
 Depth.sbx               672
-Lander.sbx              2108
+Lander.sbx              2429
 Pad.sbx                 264
 Crash.sbx               632
 vars.script             50

Tests/expected/cosmosRun.out

@@ -15,7 +15,7 @@ Mode.sbx                48
 Flip.sbx                173
 Sprite.sbx              442
 Depth.sbx               672
-Lander.sbx              2108
+Lander.sbx              2429
 Pad.sbx                 264
 Crash.sbx               632
 vars.script             50

Tests/expected/cosmosSlowDisk.out

@@ -13,7 +13,7 @@ Mode.sbx                48
 Flip.sbx                173
 Sprite.sbx              442
 Depth.sbx               672
-Lander.sbx              2108
+Lander.sbx              2429
 Pad.sbx                 264
 Crash.sbx               632
 vars.script             50

Tests/expected/cosmosSprite.out

@@ -22,7 +22,7 @@ Mode.sbx                48
 Flip.sbx                173
 Sprite.sbx              442
 Depth.sbx               672
-Lander.sbx              2108
+Lander.sbx              2429
 Pad.sbx                 264
 Crash.sbx               632
 vars.script             50