Add one layer of indirection in subsystem memory management

This allows optional subsystems to not needlessly reserve too much
system memory and it also reduces offsets bookkeeping.

dictionary.txt

@@ -21,6 +21,23 @@ directly, but as part of another word.
 
 "*I*" in description indicates an IMMEDIATE word.
 
+*** Symbols ***
+
+Throughout words, different symbols are used in different contexts, but we try
+to been consistent in their use. Here's their definitions:
+
+! - Store
+@ - Fetch
+$ - Initialize
+^ - Arguments in their opposite order
+> - Pointer in a buffer
+( - Lower boundary
+) - Upper boundary
+< - Input
+* - Word indirection (pointer to word)
+~ - Container for native code. Usually not an executable word.
+? - Is it ...? (example: IMMED?)
+
 *** Defining words ***
 (find)      a -- a f        Read at a and find it in dict. If found, f=1 and
                             a = wordref. If not found, f=0 and a = string addr.

emul/forth/run.fs

@@ -1 +1 @@
-: INIT (c<$) INTERPRET ;
+: INIT RDLN$ Z80A$ INTERPRET ;

forth/readln.fs

@@ -8,22 +8,23 @@
   routine. )
 
 64 CONSTANT INBUFSZ
-( points to INBUF )
-: IN( 0x53 RAM+ ;
-( points to INBUF's end )
-: IN) 0x55 RAM+ ;
+: RDLNMEM+ 0x53 RAM+ @ + ;
 ( current position in INBUF )
-: IN> 0x57 RAM+ ;
+: IN> 0 RDLNMEM+ ;
+( points to INBUF )
+: IN( 2 RDLNMEM+ ;
+( points to INBUF's end )
+: IN) INBUFSZ 2 + RDLNMEM+ ;
 
 ( flush input buffer )
 ( set IN> to IN( and set IN> @ to null )
-: (infl) 0 IN( @ DUP IN> ! ! ;
+: (infl) 0 IN( DUP IN> ! ! ;
 
 ( handle backspace: go back one char in IN>, if possible, then
   emit SPC + BS )
 : (inbs)
     ( already at IN( ? )
-    IN> @ IN( @ = IF EXIT THEN
+    IN> @ IN( = IF EXIT THEN
     IN> @ 1 - IN> !
     SPC BS
 ;
@@ -32,7 +33,7 @@
   should continue, that is, whether CR was not met. )
 : (rdlnc)                   ( -- f )
     ( buffer overflow? same as if we typed a newline )
-    IN> @ IN) @ = IF 0x0a ELSE KEY THEN     ( c )
+    IN> @ IN) = IF 0x0a ELSE KEY THEN     ( c )
     ( del? same as backspace )
     DUP 0x7f = IF DROP 0x8 THEN
     ( lf? same as cr )
@@ -58,7 +59,7 @@
     FLAGS @ 0x1 AND NOT IF '>' EMIT SPC THEN
     (infl)
     BEGIN (rdlnc) NOT UNTIL
-    LF IN( @ IN> !
+    LF IN( IN> !
 ;
 
 ( And finally, implement a replacement for the (c<) routine )
@@ -71,13 +72,12 @@
 ;
 
 ( Initializes the readln subsystem )
-: (c<$)
-    H@ IN( !
-    INBUFSZ ALLOT
-    H@ IN) !
-    ( We need two extra bytes. 1 for the last typed 0x0a and
-      one for the following NULL. )
-    2 ALLOT
+: RDLN$
+    ( 53 == rdln's memory )
+    H@ 0x53 RAM+ !
+    ( 2 for IN>, plus 2 for extra bytes after buffer: 1 for
+      the last typed 0x0a and one for the following NULL. )
+    INBUFSZ 4 + ALLOT
     (infl)
     ['] (rdln<) 0x0c RAM+ !
 ;

forth/z80a.fs

@@ -1,21 +1,11 @@
 ( Z80 assembler )
 
-( Splits word into msb/lsb, lsb being on TOS )
-: SPLITB
-    256 /MOD SWAP
-;
-
+: Z80AMEM+ 0x59 RAM+ @ + ;
 
 ( H@ offset at which we consider our PC 0. Used to compute
   PC. To have a proper PC, call  "H@ ORG !" at the beginning
   of your assembly process. )
-: ORG 0x59 RAM+ ;
-: PC H@ ORG @ - ;
-
-( A, spits an assembled byte, A,, spits an assembled word
-  Both increase PC. To debug, change C, to .X )
-: A, C, ;
-: A,, SPLITB A, A, ;
+: ORG 0 Z80AMEM+ ;
 
 ( Labels are a convenient way of managing relative jump
   calculations. Backward labels are easy. It is only a matter
@@ -27,13 +17,31 @@
   To avoid using dict memory in compilation targets, we
   pre-declare label variables here, which means we have a
   limited number of it. For now, 6 ought to be enough. )
+: L1 2 Z80AMEM+ ;
+: L2 4 Z80AMEM+ ;
+: L3 6 Z80AMEM+ ;
+: L4 8 Z80AMEM+ ;
+: L5 10 Z80AMEM+ ;
+: L6 12 Z80AMEM+ ;
 
-: L1 0x5b RAM+ ;
-: L2 0x5d RAM+ ;
-: L3 0x5f RAM+ ;
-: L4 0x61 RAM+ ;
-: L5 0x63 RAM+ ;
-: L6 0x65 RAM+ ;
+: Z80A$
+    ( 59 == z80a's memory )
+    H@ 0x59 RAM+ !
+    14 ALLOT
+;
+
+( Splits word into msb/lsb, lsb being on TOS )
+: SPLITB
+    256 /MOD SWAP
+;
+
+
+: PC H@ ORG @ - ;
+
+( A, spits an assembled byte, A,, spits an assembled word
+  Both increase PC. To debug, change C, to .X )
+: A, C, ;
+: A,, SPLITB A, A, ;
 
 ( There are 2 label types: backward and forward. For each
   type, there are two actions: set and write. Setting a label

notes.txt

@@ -89,17 +89,10 @@ RAMSTART   INITIAL_SP
 +2e        BOOT C< PTR
 +4e        INTJUMP
 +51        CURRENTPTR
-+53        readln's IN(
-+55        readln's IN)
-+57        readln's IN>
-+59        z80a's ORG
-+5b        z80a's L1
-+5d        z80a's L2
-+5f        z80a's L3
-+61        z80a's L4
-+63        z80a's L5
-+65        z80a's L6
-+67        FUTURE USES
++53        readln's variables
++55        FUTURE USES
++59        z80a's variables
++5b        FUTURE USES
 +70        DRIVERS
 +80        RAMEND