Tweak Console Takeover Mechanism

Based on input from Martin R, the console takeover mechanism has been modified to require that the space bar be pressed twice in a row on the character unit desiring to be the console.  This reduces the chance of a spurious console takeover due to garbage input on serial ports.

Source/Doc/UserGuide.md

@@ -903,23 +903,23 @@ If your system has more than one character unit, then the Boot Loader
 will "poll" all of the character devices for a request to make any of 
 the alternate character devices the active console.  This is called a 
 console takeover request.  This functionality must be enabled in the ROM
-build configuration, but it is for all standard ROMs.
+build configuration, but currently it is for all standard ROMs.
 
-To request a console takeover, you just press the \<space\> character
-at the port or terminal that you want to move the console to.  The
-terminal or communication software **must** be configured for the
-default serial port speed and data bits for this to work.
+To request a console takeover, you just press the \<space\> character 
+twice in a row at the port or terminal that you want to move the console
+to.  The terminal or communication software **must** be configured for 
+the default serial port speed and data bits for this to work.
 
 A takeover request is only possible while the active console is
 showing the Boot Loader prompt prior to typing any characters at
 the active console.  In other words, once you start typing at the
 active console prompt, the takeover polling is suspended.  If you have
 started typing characters, you can press \<enter\> at the active
-console to get a new Boot Loader prompt and reactivate the polling.
+console to get a fresh Boot Loader prompt and reactivate the polling.
 
 If you have built a custom ROM that includes an automatic boot
 command with a timeout, then performing a console takeover will
-abort the timeout process and the automatic command will not be
+abort the timeout process and the automatic boot command will not be
 performed.
 
 ## Front Panel

Source/HBIOS/romldr.asm

@@ -265,6 +265,18 @@ prompt:
 	call 	dsky_beep
 	call 	dsky_l2on
 #endif
+;
+	; purge any garbage on the line
+	call	delay			; wait for prompt to be sent
+	ld	b,0			; failsafe max iterations
+purge:
+	call	cst			; anything there?
+	jr	z,wtkey			; if not, move on
+	call	cin			; read and discard
+	djnz	purge			; and loop till no more
+;
+	or	$ff			; initial value
+	ld	(conpend),a		; ... for conpoll routine
 ;
 wtkey:
 	; wait for a key or timeout
@@ -319,9 +331,10 @@ clrbuf1:
 ;=======================================================================
 ;
 ; Poll all character units in system for a console takeover request.
-; A takeover request is just pressing <space> at the port that wants
-; to takeover.  Return with ZF set if a console takeover was requested.
-; If so, the requested console unit will be recorded in (newcon).
+; A takeover request consists of pressing the <space> twice in a row.
+; at the character unit that wants to be the console.  Return with ZF
+; set if a console takeover was requested. If so, the requested console
+; unit will be recorded in (newcon).
 ;
 #if (BIOS == BIOS_WBW)
   #if (AUTOCON)
@@ -329,7 +342,6 @@ clrbuf1:
 conpoll:
 	; save active console unit
 	ld	a,(curcon)
-	;ld	(savcon),a
 	ld	e,a			; save in E
 ;
 	; loop through all char ports
@@ -347,7 +359,14 @@ conpoll1:
 	call	cin			; get char
 	cp	' '			; space char?
 	jr	nz,conpoll2		; if not, move on
-	jr	conpoll3		; space char typed, take console
+;
+	; a <space> char was typed.  check to see if we just saw a
+	; <space> from this same unit.
+	ld	a,(conpend)		; pending con unit to A
+	cp	c			; compare to active unit
+	jr	z,conpoll3		; if =, second <space>, take con
+	ld	a,c			; if not, unit to A
+	ld	(conpend),a		; and update pending console
 ;
 conpoll2:
 	inc	c			; next char unit
@@ -2498,6 +2517,7 @@ dskyact		.db	0		; DSKY active if != 0
 curcon		.db	CIO_CONSOLE	; current console unit
 ciocnt		.db	1		; count of char units
 savcon		.db	0		; con save for conpoll
+conpend		.db	$ff		; pending con unit (first <space> pressed)
 #endif
 
 ;

Source/ver.inc

@@ -2,7 +2,7 @@
 #DEFINE	RMN	5
 #DEFINE	RUP	0
 #DEFINE	RTP	0
-#DEFINE BIOSVER	"3.5.0-dev.7"
+#DEFINE BIOSVER	"3.5.0-dev.8"
 #define rmj	RMJ
 #define rmn	RMN
 #define rup	RUP

Source/ver.lib

@@ -3,5 +3,5 @@ rmn	equ	5
 rup	equ	0
 rtp	equ	0
 biosver	macro
-	db	"3.5.0-dev.7"
+	db	"3.5.0-dev.8"
 	endm