Allow Telnet65 to send ASCII code 0 - on the Apple II.

Chris made me aware that ASCII code 0 actually is a valid character (usually entered as Ctrl-Space or Ctrl-@) and that it is actually used (i.e. by EMACS).

The Apple II allows to natively enter the ASCII code 0 via Ctrl-@. However so far get_key_if_available returned 0 in accumulator to signal that no key was pressed. In order to allow the Apple II get_key_if_available to return the ASCII code 0 in the accumulator I changed it to use the carry flag to signal that no key was pressed.

Because get_key_if_available needs of course to behave the same on all targets I changed the other implementations to use the carry flag too.

Unfortunately I don't know enough about input capabilities of the C64 to decide on how to best get Telnet65 to send ASCII code 0 there.

apps/telnet65.s

@@ -228,7 +228,7 @@ telnet_main_entry:
   ldax #iac_response_buffer
   jsr tcp_send
 : jsr get_key_if_available
-  beq @check_timeout
+  bcc @check_timeout
   ldx #0
   stx tcp_send_data_len
   stx tcp_send_data_len+1

drivers/a2input.s

@@ -18,15 +18,17 @@ abort_key: .byte $9b            ; ESC
 
 ; use Apple 2 monitor ROM function to read from keyboard
 ; inputs: none
-; outputs: A contains ASCII code of key pressed
+; outputs: A contains ASCII value of key just pressed
 get_key = $fd0c
 
 ; inputs: none
-; outputs: A contains ASCII value of key just pressed (0 if no key pressed)
+; outputs: sec if key pressed, clear otherwise
+;          A contains ASCII value of key just pressed
 get_key_if_available:
+  sec
   lda $c000                     ; current key pressed
   bmi got_key
-  lda #0
+  clc
   rts
 
 ; process inbound ip packets while waiting for a keypress

drivers/a2vt100.s

@@ -879,6 +879,7 @@ aDDigE  rts
 
 ProcOut
         lda kta,y   ; keyboard to ASCII
+        cmp #$ff
         beq POrts   ; ignore key
         cmp #$fe
         beq CmdKey  ; command key
@@ -1710,7 +1711,7 @@ ltsc;_0  _1  _2  _3  _4  _5  _6  _7  _8  _9  _a  _b  _c  _d  _e  _f
 ; input for sending over the serial
 ; line.
 ;
-; ascii = $00 means ignore key
+; ascii = $ff means ignore key
 ; ascii = $fe means do something
 ;             complicated (command key)
 ; -------------------------------------
@@ -1719,7 +1720,7 @@ kta ;_0  _1  _2  _3  _4  _5  _6  _7  _8  _9  _a  _b  _c  _d  _e  _f
 
 ; --- Control chars ------------------------------------------------
 ;                                    {←}     {↓} {↑}
-;        ^A  ^B  ^C  ^D  ^E  ^F  ^G  ^H  ^I  ^J  ^K  ^L  ^M  ^N  ^O
+;    ^@  ^A  ^B  ^C  ^D  ^E  ^F  ^G  ^H  ^I  ^J  ^K  ^L  ^M  ^N  ^O
 .byt $00,$01,$02,$03,$04,$05,$06,$07,$fe,$09,$fe,$fe,$0c,$0d,$0e,$0f  ; 0_
 ;                        {→}
 ;    ^P  ^Q  ^R  ^S  ^T  ^U  ^V  ^W  ^X  ^Y  ^Z  ^[  ^\  ^]  ^^  ^_

drivers/atrinput.s

@@ -24,15 +24,16 @@ kname:     .byte "K:",155
 ; outputs: A contains ASCII value of key just pressed
 get_key:
   jsr get_key_if_available
-  beq get_key
+  bcc get_key
   rts
 
 ; inputs: none
-; outputs: A contains ASCII value of key just pressed (0 if no key pressed)
+; outputs: sec if key pressed, clear otherwise
+;          A contains ASCII value of key just pressed
 get_key_if_available:
   lda CH                        ; GLOBAL VARIABLE FOR KEYBOARD
   cmp #255
-  beq @nokey
+  beq no_key
   ldx iocb                      ; K: already open?
   bne @read
   ldx #$40                      ; IOCB to use for keyboard input
@@ -55,16 +56,14 @@ get_key_if_available:
   jsr CIOV                      ; vector to CIO
   ldx #255
   stx CH                        ; GLOBAL VARIABLE FOR KEYBOARD
-  rts
-@nokey:
-  lda #0
+  sec
   rts
 
 ; process inbound ip packets while waiting for a keypress
 get_key_ip65:
   jsr ip65_process
   jsr get_key_if_available
-  beq get_key_ip65
+  bcc get_key_ip65
   rts
 
 ;check whether the abort key is being pressed
@@ -72,6 +71,7 @@ get_key_ip65:
 ;outputs: sec if abort key pressed, clear otherwise
 check_for_abort_key:
   ; TODO: implement actual check
+no_key:
   clc
   rts
 
@@ -82,16 +82,16 @@ check_for_abort_key:
 ; Version 1.1 (the "License"); you may not use this file except in
 ; compliance with the License. You may obtain a copy of the License at
 ; http://www.mozilla.org/MPL/
-; 
+;
 ; Software distributed under the License is distributed on an "AS IS"
 ; basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the
 ; License for the specific language governing rights and limitations
 ; under the License.
-; 
+;
 ; The Original Code is ip65.
-; 
+;
 ; The Initial Developer of the Original Code is Jonno Downes,
 ; jonno@jamtronix.com.
 ; Portions created by the Initial Developer are Copyright (C) 2009
-; Jonno Downes. All Rights Reserved.  
+; Jonno Downes. All Rights Reserved.
 ; -- LICENSE END --

drivers/c64input.s

@@ -24,21 +24,26 @@ get_key:
   sty $cc                       ; cursor on
 @loop:
   jsr get_key_if_available
-  beq @loop
+  bcc @loop
   ldy #1
   sty $cc                       ; cursor off
   rts
 
 ; use C64 Kernel ROM function to read a key
 ; inputs: none
-; outputs: A contains ASCII value of key just pressed (0 if no key pressed)
-get_key_if_available = $f142    ; not officially documented - where F13E (GETIN) falls through to if device # is 0 (KEYBD)
+; outputs: sec if key pressed, clear otherwise
+;          A contains ASCII value of key just pressed
+get_key_if_available:
+  jsr $f142                     ; not officially documented - where F13E (GETIN) falls through to if device # is 0 (KEYBD)
+  beq no_key
+  sec
+  rts
 
 ; process inbound ip packets while waiting for a keypress
 get_key_ip65:
   jsr ip65_process
   jsr get_key_if_available
-  beq get_key_ip65
+  bcc get_key_ip65
   rts
 
 ; check whether the abort key is being pressed
@@ -47,16 +52,16 @@ get_key_ip65:
 check_for_abort_key:
   lda $cb                       ; current key pressed
   cmp abort_key
-  bne @not_abort
+  bne no_key
 @flush_loop:
   jsr get_key_if_available
-  bne @flush_loop
+  bcs @flush_loop
   lda $cb                       ; current key pressed
   cmp abort_key
   beq @flush_loop
   sec
   rts
-@not_abort:
+no_key:
   clc
   rts
 

drivers/vic20input.s

@@ -16,7 +16,7 @@ abort_key: .byte $18            ; RUN/STOP
 
 .code
 
-; use Vic 20 Kernel ROM function to read a key
+; use VIC 20 Kernel ROM function to read a key
 ; inputs: none
 ; outputs: A contains ASCII value of key just pressed
 get_key:
@@ -24,21 +24,26 @@ get_key:
   sty $cc                       ; cursor on
 @loop:
   jsr get_key_if_available
-  beq @loop
+  bcc @loop
   ldy #1
   sty $cc                       ; cursor off
   rts
 
 ; use VIC 20 Kernel ROM function to read a key
 ; inputs: none
-; outputs: A contains ASCII value of key just pressed (0 if no key pressed)
-get_key_if_available = $f1f9    ; not officially documented - where F1f5 (GETIN) falls through to if device # is 0 (KEYBD)
+; outputs: sec if key pressed, clear otherwise
+;          A contains ASCII value of key just pressed
+get_key_if_available:
+  jsr $f1f9                     ; not officially documented - where F1F5 (GETIN) falls through to if device # is 0 (KEYBD)
+  beq no_key
+  sec
+  rts
 
 ; process inbound ip packets while waiting for a keypress
 get_key_ip65:
   jsr ip65_process
   jsr get_key_if_available
-  beq get_key_ip65
+  bcc get_key_ip65
   rts
 
 ; check whether the abort key is being pressed
@@ -47,16 +52,16 @@ get_key_ip65:
 check_for_abort_key:
   lda $cb                       ; current key pressed
   cmp abort_key
-  bne @not_abort
+  bne no_key
 @flush_loop:
   jsr get_key_if_available
-  bne @flush_loop
+  bcs @flush_loop
   lda $cb                       ; current key pressed
   cmp abort_key
   beq @flush_loop
   sec
   rts
-@not_abort:
+no_key:
   clc
   rts