Reimplement Duodyne boot recovery

Add feature description in documentation.

Source/Doc/SystemGuide.md

@@ -499,6 +499,25 @@ The startup then proceeds very much like the Application Boot
 process described above.  HBIOS is installed in its operating bank
 and control is passed to the Boot Loader.
 
+## Boot Recovery
+
+To assist users when driver faults or misconfiguration causes a boot 
+failure, RomWBW supports a limited recovery cabability.  This is 
+acheived by allowing the user to reboot their machine, loading
+a minimal driver set.  Implementation of this feature requires a
+hardware input "BOOT RECOVERY" button to be available and 
+appropriate software configuration to be completed in the HBIOS.
+
+When implemented, holding the "BOOT RECOVERY" button in after a 
+reset or power cycle will cause the normal driver load process to
+be skipped in preference to a minimal set of drivers being loaded.
+
+Typically this would be: Serial communication, RAM disk and parallel
+port IDE interface drivers.
+
+Platforms supporting this option currently are the MBC, Duodyne and
+latter version of the ECB-SBC-V3.
+ 
 # Driver Model
 
 The framework code for bank switching also allows hardware drivers to be

Source/HBIOS/cfg_DUO.asm

@@ -54,6 +54,7 @@ HBIOS_MUTEX	.SET	FALSE		; ENABLE REENTRANT CALLS TO HBIOS (ADDS OVERHEAD)
 USELZSA2	.SET	TRUE		; ENABLE FONT COMPRESSION
 TICKFREQ	.SET	50		; DESIRED PERIODIC TIMER INTERRUPT FREQUENCY (HZ)
 ;
+BT_REC_TYPE	.SET	BT_REC_DUORI	; BOOT RECOVERY METHOD TO USE
 BOOT_TIMEOUT	.SET	-1		; AUTO BOOT TIMEOUT IN SECONDS, -1 TO DISABLE, 0 FOR IMMEDIATE
 BOOT_DELAY	.SET	0		; FIXED BOOT DELAY IN SECONDS PRIOR TO CONSOLE OUTPUT
 AUTOCON		.SET	FALSE		; ENABLE CONSOLE TAKEOVER AT LOADER PROMPT

Source/HBIOS/cfg_MASTER.asm

@@ -54,6 +54,7 @@ HBIOS_MUTEX	.EQU	FALSE		; ENABLE REENTRANT CALLS TO HBIOS (ADDS OVERHEAD)
 USELZSA2	.EQU	FALSE		; ENABLE FONT COMPRESSION
 TICKFREQ	.EQU	50		; DESIRED PERIODIC TIMER INTERRUPT FREQUENCY (HZ)
 ;
+BT_REC_TYPE	.EQU	BT_REC_NONE	; BOOT RECOVERY METHOD TO USE
 BOOT_TIMEOUT	.EQU	-1		; AUTO BOOT TIMEOUT IN SECONDS, -1 TO DISABLE, 0 FOR IMMEDIATE
 BOOT_DELAY	.EQU	0		; FIXED BOOT DELAY IN SECONDS PRIOR TO CONSOLE OUTPUT
 AUTOCON		.EQU	FALSE		; ENABLE CONSOLE TAKEOVER AT LOADER PROMPT

Source/HBIOS/std.asm

@@ -102,11 +102,10 @@ BT_AUTO		.EQU	2		; AUTO SELECT BOOT_DEFAULT AFTER BOOT_TIMEOUT
 ;
 BT_REC_NONE	.EQU	0		; NO RECOVERY MODE
 BT_REC_FORCE	.EQU	1		; FORCE BOOT RECOVERY MODE
-BT_REC_SBC01	.EQU	2		; ECB-SBCV2 - BIT 1 RTC HIGH
+BT_REC_SBCB0	.EQU	2		; ECB-SBCV2 - BIT 0 RTC HIGH
 BT_REC_SBC1B	.EQU	3		; ECB-SBCV2 - 1-BIT IO PORT
 BT_REC_SBCRI	.EQU	4		; ECB-SBCV2 - 16550 UART RING INDICATOR LINE
-;
-BT_REC_TYPE	.EQU	BT_REC_NONE	; BOOT RECOVERY METHOD TO USE
+BT_REC_DUORI	.EQU	5		; DUO MULTI I/O - TL16C2552FN UART RING INDICATOR LINE
 ;
 ; FLOPPY DISK MEDIA SELECTIONS (ID'S MUST BE INDEX OF ENTRY IN FCD_TBL)
 ;