grid: Add CURSOR! to the grid protocol

With the move of CVM's forth to the grid protocol, we've lost the
cursor's visual indication. Now, we have it back.

The challenge now is in implementing it in SMS' text mode. In mode
4, it's easy to mark a cell as inverted, but in text mode, that's
not possible.

blk.fs

@@ -2214,24 +2214,24 @@ See doc/grid.txt.
 Load range: B402-B403
 ( ----- 402 )
 : XYPOS [ GRID_MEM LITN ] ; : XYMODE [ GRID_MEM LITN ] 2+ ;
-: _cl* COLS LINES * ;
-: AT-XY ( x y -- ) COLS * + _cl* MOD XYPOS ! ;
+'? CURSOR! NIP NOT [IF] : CURSOR! DROP ; [THEN]
+: XYPOS! COLS LINES * MOD DUP CURSOR! XYPOS ! ;
+: AT-XY ( x y -- ) COLS * + XYPOS! ;
 '? NEWLN NIP NOT [IF]
 : NEWLN ( ln -- ) COLS * DUP COLS + SWAP DO 0 I CELL! LOOP ;
 [THEN]
 : _lf XYMODE C@ IF EXIT THEN
     XYPOS @ COLS / 1+ LINES MOD DUP NEWLN
-    COLS * XYPOS ! ;
-: _bs 0 ( blank ) XYPOS @ TUCK CELL! ( pos ) 1-
-    _cl* MOD XYPOS ! ;
+    COLS * XYPOS! ;
+: _bs 0 ( blank ) XYPOS @ TUCK CELL! ( pos ) 1- XYPOS! ;
 ( ----- 403 )
 : (emit)
     DUP 0x08 = IF DROP _bs EXIT THEN
     DUP 0x0d = IF DROP _lf EXIT THEN
     0x20 - DUP 0< IF DROP EXIT THEN
     XYPOS @ CELL!
-    XYPOS @ 1+ DUP COLS MOD IF XYPOS ! ELSE _lf THEN ;
-: GRID$ 0 XYPOS ! 0 XYMODE C! ;
+    XYPOS @ 1+ DUP COLS MOD IF XYPOS! ELSE _lf THEN ;
+: GRID$ 0 XYPOS! 0 XYMODE C! ;
 ( ----- 410 )
 PS/2 keyboard subsystem
 

cvm/forth.fs

@@ -1,6 +1,6 @@
 : COLS 80 ; : LINES 32 ;
-: CELL! ( g pos -- )
-    COLS /MOD 6 PC! ( y ) 5 PC! ( x ) 0x20 + 0 PC! ;
+: CURSOR! ( pos -- ) COLS /MOD 6 PC! ( y ) 5 PC! ( x ) ;
+: CELL! ( g pos -- ) CURSOR! 0x20 + 0 PC! ;
 : NEWLN ( ln -- ) DROP 0xa 0 PC! ;
 
 SYSVARS 0x70 + CONSTANT GRID_MEM

doc/protocol.txt

@@ -48,6 +48,7 @@ CELL!     g pos -- Set glyph at pos
 
 Optional:
 NEWLN     ln --    "Enter" line ln
+CURSOR!   pos --   Set cursor's position
 
 "pos" is a simple number (y * cols) + x. For example, if we
 have 40 columns per line, the position (x, y) (12, 10) is 412.
@@ -69,3 +70,7 @@ time.
 If it's not defined, the grid system uses multiple CELL!
 calls to clear it. On some devices, this is highly inefficient.
 Drivers for those devices should define NEWLINE.
+
+CURSOR! is called whenever we change the cursor's position. If
+not implemented, it will be a noop. It is never called with an
+out of range "pos" (greater than COLS*LINES).