Make KEY non-blocking

... and rename it to KEY?. Then, add KEY from KEY? for its blocking
version.

I need this for an upcoming Remote Shell feature. If a Collapse OS
system remotely controls another shell, it needs to be able to poll
both the remote system and the local keyboard at the same time. A
blocking KEY is incompatible with this.

In some places, the polling mechanism doesn't make sense, so this
new KEY? always returns a character. In some places, I just haven't
implemented the mechanism yet, so I kept the old blocking code and
added a "always 1" flag as a temporary shim.

I have probably broken something, but in emulators, Collapse OS runs
fine. It's an important reminder of what will be lost with the new
"dogfooding" approach (see recent mailing list message): without
emulators, it's much harder to to sweeping changes like this without
breaking stuff.

It's fine, I don't expect many more of these core changes to the
system. It's nearly feature-complete.

arch/8086/pcat/blk.fs

@@ -16,13 +16,13 @@ BX 0 MOVxI, 0x13 INT, ( read sectors 2-15 of boot floppy )
 ( TODO: reading 12 sectors like this probably doesn't work
   on real vintage PC/AT with floppy. Make this more robust. )
 0x800 0 JMPf,
-ORG @ 0x1fe + HERE ! 0x55 C,* 0xaa C,*
+ORG @ 0x1fe + HERE ! 0x55 C, 0xaa C,
 ( ----- 604 )
 CODE (emit) 1 chkPS,
     AX POPx, AH 0x0e MOVri, ( print char ) 0x10 INT,
 ;CODE
-CODE (key)
+CODE (key?)
-    AH AH XORrr, 0x16 INT, AH AH XORrr, AX PUSHx,
+    AH AH XORrr, 0x16 INT, AH AH XORrr, AX PUSHx, AX PUSHx,
 ;CODE
 ( ----- 606 )
 CODE 13H08H ( driveno -- cx dx )

arch/z80/rc2014/blk.fs

@@ -7,15 +7,15 @@
   6850_IO for data register.
   CTL numbers used: 0x16 = no interrupt, 8bit words, 1 stop bit
   64x divide. 0x56 = RTS high )
-CODE 6850<
+: _rts 0x16 ( RTS low ) [ 6850_CTL LITN ] PC! ;
-    A 0x16 ( RTS low ) LDri, 6850_CTL OUTiA,
+: _rts^ 0x56 ( RTS high ) [ 6850_CTL LITN ] PC! ;
-    BEGIN,
+: 6850<? ( -- c? f )
-        6850_CTL INAi, 0x01 ANDi, ( is ACIA rcv buf full? )
+    [ 6850_CTL LITN ] PC@ 1 AND ( is rcv buff full ? )
-    JRZ, ( no, loop ) AGAIN,
+    NOT IF ( RTS low, then wait 1ms and try again )
-    A 0x56 ( RTS high ) LDri, 6850_CTL OUTiA,
+        _rts 10 TICKS ( 1ms ) _rts^
-    ( we have data, fetch and push )
+        [ 6850_CTL LITN ] PC@ 1 AND ( is rcv buff full ? )
-    6850_IO INAi, PUSHA,
+        NOT IF 0 EXIT THEN
-;CODE
+    THEN [ 6850_IO LITN ] PC@ ( c ) 1 ( f ) ;
 ( ----- 602 )
 CODE 6850>
     HL POP, chkPS,
@@ -25,7 +25,7 @@ CODE 6850>
     A L LDrr, 6850_IO OUTiA,
 ;CODE
 ( ----- 603 )
-: (key) 6850< ;
+: (key?) 6850<? ;
 : (emit) 6850> ;
 : 6850$ 0x56 ( RTS high ) [ 6850_CTL LITN ] PC! ;
 ( ----- 605 )
@@ -34,17 +34,16 @@ CODE 6850>
   SIOA_DATA for ch A data register
   SIOB_CTL for ch B control register
   SIOB_DATA for ch B data register )
-CODE SIOA<
+: _<? ( io ctl -- c? f )
-    A 0x05 ( PTR5 ) LDri, SIOA_CTL OUTiA,
+    DUP ( io ctl ctl ) PC@ 1 AND ( is rcv buff full ? )
-    A 0b01101000 ( De-assert RTS ) LDri, SIOA_CTL OUTiA,
+    NOT IF ( io ctl )
-    BEGIN,
+        0x05 ( PTR5 ) OVER PC! 0b01101000 OVER PC! ( RTS low )
-        SIOA_CTL ( RR0 ) INAi, 0x01 ANDi, ( is rcv buf full? )
+        10 TICKS ( 1ms )
-    JRZ, ( no, loop ) AGAIN,
+        0x05 ( PTR5 ) OVER PC! 0b01101010 OVER PC! ( RTS high )
-    A 0x05 ( PTR5 ) LDri, SIOA_CTL OUTiA,
+        PC@ 1 AND ( is rcv buff full ? )
-    A 0b01101010 ( Assert RTS ) LDri, SIOA_CTL OUTiA,
+        NOT IF DROP 0 ( f ) EXIT THEN
-    ( we have data, fetch and push )
+    ELSE DROP THEN ( io ) PC@ ( c ) 1 ( f ) ;
-    SIOA_DATA INAi, PUSHA,
+: SIOA<? [ SIOA_DATA LITN SIOA_CTL LITN ] _<? ;
-;CODE
 ( ----- 606 )
 CODE SIOA>
     HL POP, chkPS,
@@ -60,13 +59,7 @@ CREATE _ ( init data ) 0x18 C, ( CMD3 )
     0x21 C, ( CMD2/PTR1 ) 0 C, ( WR1/Rx no INT )
 : SIOA$ 9 0 DO _ I + C@ [ SIOA_CTL LITN ] PC! LOOP ;
 ( ----- 607 )
-CODE SIOB<
+: SIOB<? [ SIOB_DATA LITN SIOB_CTL LITN ] _<? ;
-    BEGIN,
-        SIOB_CTL ( RR0 ) INAi, 0x01 ANDi, ( is rcv buf full? )
-    JRZ, ( no, loop ) AGAIN,
-    ( we have data, fetch and push )
-    SIOB_DATA INAi, PUSHA,
-;CODE
 CODE SIOB>
     HL POP, chkPS,
     BEGIN,
@@ -105,7 +98,7 @@ RS_ADDR 0x80 - CONSTANT SYSVARS
 270 LOAD  ( xcomp overrides )  283 335 LOADR ( boot.z80 )
 353 LOAD  ( xcomp core low )   605 607 LOADR ( SIO )
 419 LOAD  ( SPI relay )        423 436 LOADR ( SD Card )
-400 LOAD  ( AT28 ) : (key) SIOB< ; : (emit) SIOB> ;
+400 LOAD  ( AT28 ) : (key?) SIOA<? ; : (emit) SIOA> ;
 390 LOAD  ( xcomp core high )
 (entry) _ PC ORG @ 8 + ! ( Update LATEST )
-," SIOB$ BLK$ " EOT,
+," SIOA$ BLK$ " EOT,

arch/z80/sms/blk.fs

@@ -64,7 +64,7 @@ from it. It goes as follow:
                                                         (cont.)
 ( ----- 611 )
 This module is currently hard-wired to VDP driver, that is, it
-calls vdp's routines during (key) to update character
+calls vdp's routines during (key?) to update character
 selection.
 
 Load range: 632-637
@@ -113,15 +113,15 @@ CREATE _ '0' C, ':' C, 'A' C, '[' C, 'a' C, 0xff C,
     0xe0 AND 0xe0 <
 ;
 ( ----- 616 )
-: (key)
+: (key?) ( -- c? f )
-    _next C@ IF _next C@ 0 _next C! EXIT THEN
+    _next C@ IF _next C@ 0 _next C! 1 EXIT THEN
-    BEGIN _updsel UNTIL
+    _updsel IF
     _prevstat C@
-    0x20 ( BUTC ) OVER AND NOT IF DROP _sel C@ EXIT THEN
+    0x20 ( BUTC ) OVER AND NOT IF DROP _sel C@ 1 EXIT THEN
-    0x40 ( BUTA ) AND NOT IF 0x8 ( BS ) EXIT THEN
+    0x40 ( BUTA ) AND NOT IF 0x8 ( BS ) 1 EXIT THEN
     ( If not BUTC or BUTA, it has to be START )
-    0xd _next C! _sel C@
+    0xd _next C! _sel C@ 1
-;
+    ELSE 0 ( f ) THEN ;
 ( ----- 617 )
 : PAD$
     0xff _prevstat C! 'a' _sel C! 0 _next C! ;

arch/z80/ti84/blk.fs

@@ -129,7 +129,7 @@ Keyboard driver
 
 Load range: 566-570
 
-Implement a (key) word that interpret keystrokes from the
+Implement a (key?) word that interpret keystrokes from the
 builtin keyboard. The word waits for a digit to be pressed and
 returns the corresponding ASCII value.
 
@@ -189,35 +189,30 @@ CREATE _atbl
     0x20 C, 'Y' C, 'T' C, 'O' C, 'J' C, 'E' C, 'B' C, 0 C,
     0 C, 'X' C, 'S' C, 'N' C, 'I' C, 'D' C, 'A' C, 0x80 C,
     0 C, 0 C, 0 C, 0 C, 0 C, 0x81 ( 2nd ) C, 0 C, 0x7f C,
-: _2nd@ [ KBD_MEM LITN ] C@ 1 AND ;
+: _@ [ KBD_MEM LITN ] C@ ; : _! [ KBD_MEM LITN ] C! ;
-: _2nd! [ KBD_MEM LITN ] C@ 0xfe AND + [ KBD_MEM LITN ] C! ;
+: _2nd@ _@ 1 AND ; : _2nd! _@ 0xfe AND + _! ;
-: _alock@ [ KBD_MEM LITN ] C@ 2 AND ;
+: _alpha@ _@ 2 AND ; : _alpha! 2 * _@ 0xfd AND + _! ;
-: _alock^ [ KBD_MEM LITN ] C@ 2 XOR [ KBD_MEM LITN ] C! ;
+: _alock@ _@ 4 AND ; : _alock^ _@ 4 XOR _! ;
 ( ----- 619 )
 : _gti ( -- tindex, that it, index in _dtbl or _atbl )
-    0 ( gid ) 0 ( dummy )
+    7 0 DO
-    BEGIN ( loop until a digit is pressed )
+        1 I LSHIFT 0xff -^ ( group dmask ) _get
-        DROP
+        DUP 0xff = IF DROP ELSE I ( dmask gid ) LEAVE THEN
-        1+ DUP 7 = IF DROP 0 THEN ( inc gid )
+    LOOP _wait
-        1 OVER LSHIFT 0xff -^ ( group dmask ) _get
+    SWAP ( gid dmask )
-    DUP 0xff = NOT UNTIL _wait
-    ( gid dmask )
     0xff XOR ( dpos ) 0 ( dindex )
     BEGIN 1+ 2DUP RSHIFT NOT UNTIL 1-
     ( gid dpos dindex ) NIP
     ( gid dindex ) SWAP 8 * + ;
 ( ----- 620 )
-: _tbl^ ( swap input tbl )
+: (key?) ( -- c? f )
-    _atbl = IF _dtbl ELSE _atbl THEN ;
+    0 _get 0xff = IF ( no key pressed ) 0 EXIT THEN
-: (key)
+    _alpha@ _alock@ IF NOT THEN IF _atbl ELSE _dtbl THEN
-    0 _2nd! 0 ( lastchr ) BEGIN
+    _gti + C@ ( c )
-        _alock@ IF _atbl ELSE _dtbl THEN
+    DUP 0x80 = IF _2nd@ IF _alock^ ELSE 1 _alpha! THEN THEN
-        OVER 0x80 ( alpha ) =
+    DUP 0x81 = _2nd!
-            IF _tbl^ _2nd@ IF _alock^ THEN THEN
+    DUP 0 0x80 >< IF ( we have something )
-        SWAP 0x81 = _2nd!
+    ( lower? ) _2nd@ IF DUP 'A' 'Z' =><= IF 0x20 OR THEN THEN
-        _gti + C@
+        0 _2nd! 0 _alpha! 1 ( c f )
-    DUP 0 0x80 >< UNTIL ( loop if not in range )
+    ELSE ( nothing ) DROP 0 THEN ;
-    ( lowercase? )
-    _2nd@ IF DUP 'A' 'Z' =><= IF 0x20 OR THEN THEN
-;
 : KBD$ 0 [ KBD_MEM LITN ] C! ;

arch/z80/ti84/xcomp.fs

@@ -39,7 +39,7 @@ EI,
 RETI,
 
 0x03 ALLOT0 ( 0x53 )
-0x5a JP, ( 0x56 ) 0xff A, 0xa5 A, 0xff A, ( 0x5a )
+0x5a JP, ( 0x56 ) 0xff C, 0xa5 C, 0xff C, ( 0x5a )
 ( boot )
 DI,
     IM1,

arch/z80/trs80/blk.fs

@@ -11,10 +11,10 @@ There is also the RECV program at B612.
 ( ----- 602 )
 1 8 LOADR+
 ( ----- 603 )
-CODE (key)
+CODE (key?) ( -- c? f ) ( TODO: make non-blocking )
     A 0x01 LDri, ( @KEY )
     0x28 RST,
-    PUSHA,
+    PUSHA, PUSH1,
 ;CODE
 CODE (emit) EXX, ( protect BC )
     BC POP, ( c == @DSP arg ) chkPS,

arch/z80/z80mbc2/xcomp.fs

@@ -10,9 +10,9 @@ RS_ADDR 0x80 - CONSTANT SYSVARS
 CODE (emit)
     A 1 LDri, 1 OUTiA, HL POP, A L LDrr, 0 OUTiA,
 ;CODE
-CODE (key)
+CODE (key?) ( TODO: make non-blocking )
     BEGIN, 1 INAi, A INCr, JRZ, AGAIN,
-    A DECr, PUSHA,
+    A DECr, PUSHA, PUSH1,
 ;CODE
 : _sel ( sec )
 ( 32 sectors per track, 512 tracks per disk )

blk.fs

@@ -2002,7 +2002,8 @@ SYSVARS 0x0c + :** C<*
 ;
 ( del is same as backspace )
 : BS? DUP 0x7f = SWAP 0x8 = OR ;
-SYSVARS 0x55 + :** KEY
+SYSVARS 0x55 + :** KEY?
+: KEY BEGIN KEY? UNTIL ;
 ( cont.: read one char into input buffer and returns whether we
   should continue, that is, whether CR was not met. )
 ( ----- 379 )
@@ -2104,7 +2105,7 @@ SYSVARS 0x55 + :** KEY
     0x02 RAM+ CURRENT* !
     CURRENT @ 0x2e RAM+ ! ( 2e == BOOT C< PTR )
     0 0x08 RAM+ !  ( 08 == C<* override )
-    ['] (emit) ['] EMIT **! ['] (key) ['] KEY **!
+    ['] (emit) ['] EMIT **! ['] (key?) ['] KEY? **!
     ['] CRLF ['] NL **!
     ['] (boot<) ['] C<* **!
     ( boot< always has a char waiting. 06 == C<?* )
@@ -2205,7 +2206,7 @@ Load range: B402-B403
 ( ----- 410 )
 PS/2 keyboard subsystem
 
-Provides (key) from a driver providing the PS/2 protocol. That
+Provides (key?) from a driver providing the PS/2 protocol. That
 is, for a driver taking care of providing all key codes emanat-
 ing from a PS/2 keyboard, this subsystem takes care of mapping
 those keystrokes to ASCII characters. This code is designed to
@@ -2220,7 +2221,7 @@ Load range: 411-414
 
 ( A list of the values associated with the 0x80 possible scan
 codes of the set 2 of the PS/2 keyboard specs. 0 means no
-value. That value is a character that can be read in (key)
+value. That value is a character that can be read in (key?)
 No make code in the PS/2 set 2 reaches 0x80. )
 CREATE PS2_CODES
 ( 00 ) 0 C, 0 C, 0 C, 0 C, 0 C, 0 C, 0 C, 0 C,
@@ -2262,19 +2263,20 @@ CREATE PS2_CODES
 ( 78 ) 0 C, 0 C, 0 C, 0 C, 0 C, 0 C, 0 C, 0 C,
 ( ----- 414 )
 : _shift? ( kc -- f ) DUP 0x12 = SWAP 0x59 = OR ;
-: _get ( -- kc ) 0 ( dummy ) BEGIN DROP (ps2kc) DUP UNTIL ;
+: (key?) ( -- c? f )
-: (key) _get
+    (ps2kc) DUP NOT IF EXIT THEN ( kc )
-    DUP 0xe0 ( extended ) = IF ( ignore ) DROP (key) EXIT THEN
+    DUP 0xe0 ( extended ) = IF ( ignore ) DROP 0 EXIT THEN
     DUP 0xf0 ( break ) = IF DROP ( )
         ( get next kc and see if it's a shift )
-        _get _shift? IF ( drop shift ) 0 PS2_SHIFT C! THEN
+        BEGIN (ps2kc) ?DUP UNTIL ( kc )
+        _shift? IF ( drop shift ) 0 PS2_SHIFT C! THEN
         ( whether we had a shift or not, we return the next )
-        (key) EXIT THEN
+        0 EXIT THEN
-    DUP 0x7f > IF DROP (key) EXIT THEN
+    DUP 0x7f > IF DROP 0 EXIT THEN
-    DUP _shift? IF DROP 1 PS2_SHIFT C! (key) EXIT THEN
+    DUP _shift? IF DROP 1 PS2_SHIFT C! 0 EXIT THEN
     ( ah, finally, we have a gentle run-of-the-mill KC )
-    PS2_CODES PS2_SHIFT C@ IF 0x80 + THEN + C@
+    PS2_CODES PS2_SHIFT C@ IF 0x80 + THEN + C@ ( c, maybe 0 )
-    ?DUP NOT IF (key) THEN ;
+    ?DUP ( c? f ) ;
 ( ----- 418 )
 SPI relay driver
 

cvm/common.fs

@@ -75,7 +75,7 @@ H@ 4 + XCURRENT ! ( make next CODE have 0 prev field )
 0x39 CODE |L
 0x3a CODE |M
 353 LOAD ( xcomp core )
-: (key) 0 PC@ ;
+: (key?) 0 PC@ 1 ;
 : EFS@
     1 3 PC! ( read )
     |M 3 PC! 3 PC! ( blkid )

doc/dict.txt

@@ -10,6 +10,11 @@ top of stack (TOS). For example, in "a b -- c d", b is TOS
 before, d is TOS after. "R:" means that the Return Stack is
 modified.
 
+Some words have a variable stack signature, most often in pair
+with a flag. These are indicated with "?" to tell that the argu-
+ment might not be there. For example, "-- n? f" means that "n"
+might or might not be there.
+
 Word references (wordref): When we say we have a "word
 reference", it's a pointer to a word's *entry type field*. For
 example, the address that "' DUP" puts on the stack is a
@@ -236,25 +241,31 @@ STYPE    a --     EMIT all chars of string at at addr a.
 .X       n --     Print n in hex form. Always 4 characters.
                   Numbers are never considered negative.
                   "-1 .X" --> ffff
-," xxx" --     Write xxx to HERE
+," xxx" --        Write xxx to HERE
-." xxx" --     *I* Compiles string literal xxx followed by a
+." xxx" --        *I* Compiles string literal xxx followed by a
-               call to STYPE.
+                  call to STYPE.
-C<?     -- f   Returns whether there's a char waiting in buf.
+C<?     -- f      Returns whether there's a char waiting in buf.
-C<      -- c   Read one char from buffered input.
+C<      -- c      Read one char from buffered input.
-EMIT    c --   Spit char c to output stream
+EMIT    c --      Spit char c to output stream
-IN>     -- a   Address of variable containing current pos in
+IN>     -- a      Address of variable containing current pos in
-               input buffer.
+                  input buffer.
-KEY     -- c   Get char c from direct input
+KEY?    -- c? f   Polls the keyboard for a key. If a key is
-PC!     c a -- Spit c to port a
+                  pressed, f is true and c is the char. Other-
-PC@     a -- c Fetch c from port a
+                  wise, f is false and c is *not* on the stack.
-WORD    -- a   Read one word from buffered input and push its
+KEY     -- c      Get char c from direct input
-               addr. Always null terminated. If ASCII EOT is
+PC!     c a --    Spit c to port a
-               encountered, a will point to it (it is cons-
+PC@     a -- c    Fetch c from port a
-               idered a word).
+WORD    -- a      Read one word from buffered input and push its
+                  addr. Always null terminated. If ASCII EOT is
+                  encountered, a will point to it (it is cons-
+                  idered a word).
 
 There are also ascii const emitters:
 BS CR LF SPC CRLF
 
+KEY? and EMIT are ialiases to (key?) and (emit) (see TTY proto-
+col in protocol.txt). KEY is a loop over KEY?.
+
 NL is an ialias that points to CRLF by default and that should
 generally be used when we want to emit a newline.
 

doc/impl.txt

@@ -165,7 +165,7 @@ SYSVARS   FUTURE USES          +3c       BLK(*
 +08       C<* override         +43       FUTURE USES
 +0a       NL ialias            +51       CURRENTPTR
 +0c       C<*                  +53       EMIT ialias
-+0e       WORDBUF              +55       KEY ialias
++0e       WORDBUF              +55       KEY? ialias
 +2e       BOOT C< PTR          +57       FUTURE USES
 +30       IN>
 +32       IN(*                 +70       DRIVERS

doc/protocol.txt

@@ -2,15 +2,16 @@
 
 Some subsystems (and in the case of KEY and EMIT, the core) re-
 quire drivers to implement certain words in a certain way. For
-example, the core requires drivers to implement (key) and (emit)
+example, the core requires drivers to implement (key?) and
-or else it won't know how to provide a console.
+(emit) or else it won't know how to provide a console.
 
 These protocols are described here.
 
 # TTY protocol
 
-(key)      -- c    Returns the next typed key on the console.
+(key?)     -- c? f Returns whether a key has been pressed and,
-                   If none, block until there is one.
+                   if it has, returns which key. When f is
+                   false, c is *not* placed in the stack.
 (emit)     c --    Spit a character on the console.
 
 # PS/2 protocol
@@ -19,7 +20,7 @@ This protocol enables communication with a device that spits
 PS/2 keycodes.
 
 (ps2kc)   -- kc    Returns the next typed PS/2 keycode from the
-                   console. Blocking.
+                   console. 0 if nothing was typed.
 
 # SPI Relay protocol
 

emul/8086/xcomp.fs

@@ -6,7 +6,7 @@ RS_ADDR 0x80 - CONSTANT SYSVARS
 445 461 LOADR ( 8086 boot code )
 353 LOAD  ( xcomp core low )
 CODE (emit) AX POPx, 1 INT, ;CODE
-CODE (key) 2 INT, AH 0 MOVri, AX PUSHx, ;CODE
+CODE (key?) 2 INT, AH 0 MOVri, AX PUSHx, AX PUSHx, ;CODE
 : COLS 80 ; : LINES 25 ;
 CODE AT-XY ( x y ) BX POPx, AX POPx, 3 INT, ;CODE
 CODE _ BX POPx, AX POPx, 4 INT, ;CODE

emul/z80/acia.c

@@ -31,9 +31,10 @@ bool acia_has_irq(ACIA *acia)
     return acia->in_int;
 }
 
-bool acia_hasrx(ACIA *acia)
+bool acia_cantransmit(ACIA *acia)
 {
-    return acia->status & 0x01; // RDRF
+    return !(acia->status & 0x01 // RDRF
+        || acia->control & 0x40); // RTS
 }
 
 bool acia_hastx(ACIA *acia)

emul/z80/acia.h

@@ -29,7 +29,7 @@ typedef struct {
 
 void acia_init(ACIA *acia);
 bool acia_has_irq(ACIA *acia);
-bool acia_hasrx(ACIA *acia);
+bool acia_cantransmit(ACIA *acia);
 bool acia_hastx(ACIA *acia);
 uint8_t acia_read(ACIA *acia);
 void acia_write(ACIA *acia, uint8_t val);

emul/z80/rc2014.c

@@ -108,9 +108,9 @@ static bool hastx()
     return use_sio ? sio_hastx(&sio) : acia_hastx(&acia);
 }
 
-static bool hasrx()
+static bool cantransmit()
 {
-    return use_sio ? sio_hasrx(&sio) : acia_hasrx(&acia);
+    return use_sio ? !sio_hasrx(&sio) : acia_cantransmit(&acia);
 }
 
 static uint8_t _read()
@@ -241,7 +241,7 @@ int main(int argc, char *argv[])
                 break;
             }
         }
-        if (tosend && !hasrx()) {
+        if (tosend && cantransmit()) {
             _write(tosend);
             tosend = 0;
         }

emul/z80/xcomp.fs

@@ -9,7 +9,7 @@ RS_ADDR 0x80 - CONSTANT SYSVARS
 283 335 LOADR ( boot.z80 )
 353 LOAD  ( xcomp core low )
 : (emit) 0 PC! ;
-: (key) 0 PC@ ;
+: (key?) 0 PC@ 1 ;
 : EFS@
     1 3 PC! ( read )
     256 /MOD 3 PC! 3 PC! ( blkid )