Use EXITAPP instead of FLOAT to leave Ladybug

Now that the shell mechanism allows for multiple applications it makes
sense to change the way we exit Ladybug. Previously there was a FLOAT
function to disable the Ladybug application, but it is now changed to
EXITAPP which simply drops the topmost application.

It is a good idea to have a consistent way of exiting an application
and then the only logical choice is to use a key that is not normally
used. The shifted USER key is a good choice as it normally has no
function bound to it and USER is about keyboard layouts.

Some minor rearrangements are needed for this as MASKL was on that key
previously. Move MASKL and MASKR right (PRGM and ALPHA), drop ALDI
would make more sense to have on a slightly change alpha keyboard that
currently is not defined.

This frees up the PI key position, so WSIZE? is put there, as it can
be useful in calculations and as a way to check the current
settings. Setting the word size is nearby, making it a sensible
location.

doc/implementation.rst

@@ -95,9 +95,10 @@ keyboard, so that also makes some sense.
 The logical operations are held together in the usual order you say
 them, AND, OR, XOR, which also is the alphabetical order.
 
-When you feel that you need to work with floating point numbers, you
-probably want to use that PI constant, so the ``FLOAT`` operation to
-switch to floating point mode is on the PI key.
-
 Sign extension is on the ``EEX`` key, which is almost spelled the
 same.
+
+The shifted ``USER`` key performs the ``EXITAPP`` function which
+exists the Ladybug shell and takes you back to the previous shell.
+This key was chosen as it is always free and the ``USER`` key is
+related to affecting the keyboard layout.

doc/keyboard.rst

@@ -26,9 +26,9 @@ Deactivation
 ============
 
 Once activated, the HP-41 stays in integer mode until you execute the
-``FLOAT`` instruction. This can be done by pressing the shift key
-followed by the PI (0 key). It is also possible to execute the
-``FLOAT`` instruction using the ``XEQ`` key and spell it out as
+``EXITAPP`` instruction. This can be done by pressing the shift key
+followed by the USER key. It is also possible to execute the
+``EXITAPP`` instruction using the ``XEQ`` key and spell it out as
 usual.
 
 Another way to disable Ladybug is to turn the calculator off and

doc/reference.rst

@@ -28,13 +28,19 @@ well.
 
 .. index:: float mode, mode; float
 
-.. object:: FLOAT
+.. object:: EXITAPP
 
-   Switch to floating point mode, leaving integer mode. This restores
-   the keyboard and display to its normal floating point behavior.
+   Leave integer mode by exiting Ladybug and switching back to
+   floating point mode. This restores the keyboard and display to its
+   normal floating point behavior.
 
-   Integer instructions in floating point mode still works, but will
-   not display or use the dedicated keyboard.
+   Technically it leaves the current active application shell and goes
+   back to the shell that was active before it. The very last such
+   shell is the standard calculator behavior.
+
+   Integer instructions still work when the Ladybug application is
+   inactive. What happens is that the Ladybug display and keyboard
+   overrides are no longer active.
 
 
 .. index:: binary base, base; binary

src/ladybug.s

@@ -85,7 +85,7 @@ XROMno:       .equ    16
 FatStart:
               .fat    LadyHeader    ; ROM header
               FAT     Literal
-              FAT     FLOAT         ; mode change
+              FAT     EXITAPP       ; drop to previous App
               .fat    Integer
               FAT     Binary        ; base related instructions
               FAT     Octal
@@ -1013,19 +1013,16 @@ exitNoUserSTR1:
 
 ;;; **********************************************************************
 ;;;
-;;; FLOAT - restore float mode operation
+;;; EXITAPP - restore float mode operation
 ;;;
-;;; Essentially we just disable our own shell (if it exists).
+;;; In reality we exit the top application shell.
 ;;;
 ;;; **********************************************************************
 
               .section Code, reorder
-              .name   "FLOAT"
-FLOAT:        nop                   ; non-programmable
-                                    ;  (allow  mode switch in program mode)
-              ldi     .low12 ladybugShell
-              gosub   exitShell     ; must be a gosub to provide page address
-              golong  NFRPU         ; must golong as exitShell uses +3 levels
+              .name   "EXITAPP"
+EXITAPP:      gosub   exitApp
+              golong  NFRC
 
               .section Code, reorder
 noBuf:        gosub   errorMessage
@@ -5298,7 +5295,7 @@ keyTable:
               .con    BuiltinKey(0xa8) ; SF
               KeyEntry SB           ; 4
               KeyEntry AND          ; 1  (FIX key)
-              KeyEntry FLOAT        ; 0
+              KeyEntry WSIZE?       ; 0
 
               ;; Logical column 2
               .con    0x10c         ; SQRT  (C digit)
@@ -5355,9 +5352,9 @@ keyTable:
               KeyEntry RRC          ; TAN
               .con    0             ; BST
               KeyEntry CLXI         ; BACKARROW
-              KeyEntry ALDI         ; MODE ALPHA
-              KeyEntry MASKR        ; MODE PRGM
-              KeyEntry MASKL        ; MODE USER
+              KeyEntry MASKR        ; MODE ALPHA
+              KeyEntry MASKL        ; MODE PRGM
+              KeyEntry EXITAPP      ; MODE USER
               .con    0             ; OFF key special
 
 ;;; ----------------------------------------------------------------------