Add ~C! to override memory low level write routines

Also, turn AT28! and AT28, into ~AT28, pluggable into ~C!.

~AT28 doesn't check for mismatches. It was too complicated to turn
a mismatch into a compiled word we would jump to next. Data
integrity has to be checked through another path.

Also, remove MOVEW. Without indirect memory access, this word
doesn't make sense. Some AVR-specific words will have to be
defined.

blk.fs

@@ -1048,6 +1048,11 @@ VARIABLE lbluflw VARIABLE lblexec
 ( 7.373MHz target: 737t. outer: 37t inner: 16t )
 ( tickfactor = (737 - 37) / 16 )
 CREATE tickfactor 44 ,
+( Perform a byte write by taking into account the SYSVARS+3e
+  override. )
+: LD(HL)E*, SYSVARS 0x3e + LDA(i), A ORr,
+    IFZ, (HL) E LDrr, ELSE, SYSVARS 0x3e + CALL, THEN, ;
+
 ( ----- 283 )
 H@ ORG ! ( STABLE ABI )
 0 JP, ( 00, main ) NOP, ( unused ) NOP, NOP, ( 04, BOOT )
@@ -1072,6 +1077,7 @@ HERESTART [IF]
     HL HERESTART LDdi,
 [THEN]
     SYSVARS 0x04 + LD(i)HL, ( RAM+04 == HERE )
+    A XORr, SYSVARS 0x3e + LD(i)A, ( 3e == ~C! )
     DE BIN( @ 0x04 ( BOOT ) + LDd(i),
     JR, L1 FWR ( execute, B287 )
 ( ----- 286 )
@@ -1458,9 +1464,8 @@ CODE TICKS
 ( ----- 322 )
 CODE !
     HL POP, DE POP, chkPS,
-    (HL) E LDrr,
-    HL INCd,
-    (HL) D LDrr,
+    LD(HL)E*, HL INCd,
+    E D LDrr, LD(HL)E*,
 ;CODE
 CODE @
     HL POP, chkPS,
@@ -1472,14 +1477,17 @@ CODE @
 ( ----- 323 )
 CODE C!
     HL POP, DE POP, chkPS,
-    (HL) E LDrr,
-;CODE
-
+    LD(HL)E*, ;CODE
 CODE C@
     HL POP, chkPS,
     L (HL) LDrr,
-    H 0 LDri,
-    HL PUSH,
+    H 0 LDri, HL PUSH, ;CODE
+CODE ~C!
+    HL POP, chkPS,
+    SYSVARS 0x3f + LD(i)HL,
+    HLZ, ( makes A zero if Z is set ) IFNZ,
+        A 0xc3 ( JP ) LDri, THEN,
+    ( A is either 0 or c3 ) SYSVARS 0x3e + LD(i)A,
 ;CODE
 ( ----- 324 )
 CODE PC! EXX, ( protect BC )
@@ -1862,12 +1870,6 @@ SYSVARS 0x0c + :** C<*
     LOOP THEN 2DROP ;
 : MOVE, ( a u -- ) H@ OVER ALLOT SWAP MOVE ;
 ( ----- 368 )
-: MOVEW ( src dst u -- )
-    ( u ) 0 DO
-        SWAP DUP I 1 LSHIFT + C@  ( dst src x )
-        ROT TUCK I 1 LSHIFT +     ( src dst x dst )
-        C!                        ( src dst )
-    LOOP 2DROP ;
 : PREV 3 - DUP @ - ;
 : [entry] ( w -- )
     C@+ ( w+1 len ) TUCK MOVE, ( len )
@@ -2162,21 +2164,14 @@ XCURRENT @ _xapply ORG @ 0x04 ( stable ABI BOOT ) + !
 ':' X' _ 4 - C! ( give : its name )
 '(' X' _ 4 - C!
 ( ----- 400 )
-( With dst being assumed to be an AT28 EEPROM, perform C!
-  operation while doing the right thing. Checks data integrity
-  and ABORT on mismatch. )
-: _ ( n a -- wait until addr is "stable", err on mismatch )
-    ( as long as writing operation is running, IO/6 will toggle
-      at each read attempt. We know that write is finished when
-      we read the same value twice. )
-    BEGIN ( n1 a )
-        DUP C@      ( n1 a n2 )
-        OVER C@     ( n1 a n2 n3 )
-    = UNTIL
-    ( We're finished writing. do we have a mismatch? )
-    C@ SWAP 0xff AND = NOT IF ABORT" mismatch" THEN ;
-: AT28! ( n a -- ) 2DUP C! _ ;
-: AT28, ( n -- ) H@ 2DUP C! DUP 1+ HERE ! _ ;
+( Write byte E at addr HL, assumed to be an AT28 EEPROM.
+  After that, poll repeatedly that address until writing is
+  complete. )
+(entry) ~AT28 ( warning: don't touch D register )
+    (HL) E LDrr, E (HL) LDrr, ( poll ) BEGIN,
+        A (HL) LDrr, ( poll ) E CPr, ( same as old? )
+        E A LDrr, ( save old poll, Z preserved )
+    JRNZ, AGAIN, RET,
 ( ----- 401 )
 Grid subsystem
 

doc/dict.txt

@@ -152,6 +152,7 @@ J           -- n            Copy RS third item to PS
 ,        n --            Write n in HERE and advance it.
 ?        a --            Print value of addr a
 +!       n a --          Increase value of addr a by n
+~C!      a --            Set C! and ! overrides. See notes.
 C@       a -- c          Set c to byte at address a
 C@+      a -- a+1 c      Fetch c from a and inc a.
 C@-      a -- a-1 c      Fetch c from a and dec a.
@@ -173,13 +174,15 @@ MOVE     a1 a2 u --      Copy u bytes from a1 to a2, starting
 MOVE-    a1 a2 u --      Copy u bytes from a1 to a2, starting
                          with a1+u, going down.
 MOVE,    a u --          Copy u bytes from a to HERE.
-MOVEW    src dst u --    Same as MOVE, but with words
 
-MOVEW notes: this word's purpose is to interface with word-
-based systems. src and dst are addressed as *bytes* but u is a
-*word* count. Every iteration increases src and dst by 2. This
-shouldn't be used on regular memory, it will yield weird
-results. Use it with C!* ialias pointing to a word-based target.
+Notes:
+
+~C!: When supplied a non-zero address, sets the SYSVARS+3e (see
+     impl.txt) override routine address. This should link dir-
+     ectly to assembly code because we call this address. This
+     routine shouldn't end with a call to next, but rather a
+     regular assembly return. Registers used are arch-specific.
+     When supplied 0, unsets override.
 
 # Arithmetic / Bits
 

doc/impl.txt

@@ -159,10 +159,10 @@ offsets, but thankfully, there aren't many system variables.
 Here's a list of them:
 
 SYSVARS   FUTURE USES          +3c       BLK(*
-+02       CURRENT              +3e       FUTURE USES
-+04       HERE                 +40       FUTURE USES
-+06       C<?                  +42       FUTURE USES
-+08       C<* override         +44       FUTURE USES
++02       CURRENT              +3e       ~C!*
++04       HERE                 +41       FUTURE USES
++06       C<?                  +43       FUTURE USES
++08       C<* override         +45       FUTURE USES
 +0a       NL ialias            +51       CURRENTPTR
 +0c       C<*                  +53       EMIT ialias
 +0e       WORDBUF              +55       KEY ialias
@@ -193,6 +193,10 @@ for example), it can point elsewhere.
 
 BLK* "Disk blocks" in usage.txt.
 
+~C!* if nonzero, contains a jump to assembly code that overrides
+the routine that writes a byte to memory and then returns.
+Register usage is arch-dependent, see boot code for details.
+
 DRIVERS section is reserved for recipe-specific drivers.
 
 FUTURE USES section is unused for now.