From 2e6122025dcafb77444aa39d901615782ba2aece Mon Sep 17 00:00:00 2001
From: Wayne Warthen <wwarthen@gmail.com>
Date: Wed, 27 Oct 2021 15:06:24 -0700
Subject: [PATCH] RAM Disk Auto-Format Improvements

- Detect the situation where the RAM disk area is all zeroes and handle it properly as uninitialized.
---
 Source/CBIOS/cbios.asm | 22 ++++++++++++++++++++++
 Source/CPM3/boot.z80   | 11 +++++++++++
 Source/ver.inc         |  2 +-
 Source/ver.lib         |  2 +-
 4 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/Source/CBIOS/cbios.asm b/Source/CBIOS/cbios.asm
index 695c823d..4bb0b22e 100644
--- a/Source/CBIOS/cbios.asm
+++ b/Source/CBIOS/cbios.asm
@@ -2471,6 +2471,17 @@ MD_INIT4:
 	CALL	$FFFD			; DO IT (RST 08 NOT SAFE HERE)
 ;
 #IF (CLRRAMDISK == CLR_AUTO)
+	; CHECK THE FIRST SECTOR (512 BYTES) FOR ALL ZEROES.  IF SO,
+	; IT IMPLIES THE RAM IS UNINITIALIZED.
+	LD	HL,0			; START AT BEGINING OF RAM DISK
+	LD	BC,512			; COMPARE 512 BYTES
+	XOR	A			; COMPARE TO ZERO
+CLRRAM000:
+	CPI				; A - (HL), HL++, BC--
+	JR	NZ,CLRRAM00		; IF NOT ZERO, GO TO NEXT TEST
+	JP	PE,CLRRAM000		; LOOP THRU ALL BYTES
+	JR	CLRRAM2			; ALL ZEROES, JUMP TO INIT
+CLRRAM00:
 	; CHECK FIRST 32 DIRECTORY ENTRIES.  IF ANY START WITH AN INVALID
 	; VALUE, INIT THE RAM DISK.  VALID ENTRIES ARE E5 (EMPTY ENTRY) OR
 	; 0-15 (USER NUMBER).
@@ -2528,6 +2539,17 @@ CLRRAM3:
 	CALL	HB_BNKSEL		; SELECT BANK
 
 #IF (CLRRAMDISK == CLR_AUTO)
+	; CHECK THE FIRST SECTOR (512 BYTES) FOR ALL ZEROES.  IF SO,
+	; IT IMPLIES THE RAM IS UNINITIALIZED.
+	LD	HL,0			; START AT BEGINING OF RAM DISK
+	LD	BC,512			; COMPARE 512 BYTES
+	XOR	A			; COMPARE TO ZERO
+CLRRAM000:
+	CPI				; A - (HL), HL++, BC--
+	JR	NZ,CLRRAM00		; IF NOT ZERO, GO TO NEXT TEST
+	JP	PE,CLRRAM000		; LOOP THRU ALL BYTES
+	JR	CLRRAM2			; ALL ZEROES, JUMP TO INIT
+CLRRAM00:
 	; CHECK FIRST 32 DIRECTORY ENTRIES.  IF ANY START WITH AN INVALID
 	; VALUE, INIT THE RAM DISK.  VALID ENTRIES ARE E5 (EMPTY ENTRY) OR
 	; 0-15 (USER NUMBER).
diff --git a/Source/CPM3/boot.z80 b/Source/CPM3/boot.z80
index 9789cb8b..ce3fef1b 100644
--- a/Source/CPM3/boot.z80
+++ b/Source/CPM3/boot.z80
@@ -328,6 +328,17 @@ clrram:
 	;call	hb_bnksel		; select bank
 	call	0FFF3h			; select bank
 
+	; Check the first sector (512 bytes) for all zeroes.  If so,
+	; it implies the RAM is uninitialized.
+	ld	hl,0			; start at begining of ram disk
+	ld	bc,512			; compare 512 bytes
+	xor	a			; compare to zero
+clrram000:
+	cpi				; a - (hl), hl++, bc--
+	jr	nz,clrram00		; if not zero, go to next test
+	jp	pe,clrram000		; loop thru all bytes
+	jr	clrram2			; all zeroes, jump to init
+clrram00:
 	; Check first 32 directory entries.  If any start with an invalid
 	; value, init the ram disk.  Valid entries are e5 (empty entry) or
 	; 0-15 (user number).
diff --git a/Source/ver.inc b/Source/ver.inc
index 61eac6ca..2c77bb1e 100644
--- a/Source/ver.inc
+++ b/Source/ver.inc
@@ -2,4 +2,4 @@
 #DEFINE	RMN	1
 #DEFINE	RUP	1
 #DEFINE	RTP	0
-#DEFINE BIOSVER	"3.1.1-pre.131"
+#DEFINE BIOSVER	"3.1.1-pre.132"
diff --git a/Source/ver.lib b/Source/ver.lib
index 7c8580d2..d12c7674 100644
--- a/Source/ver.lib
+++ b/Source/ver.lib
@@ -3,5 +3,5 @@ rmn	equ	1
 rup	equ	1
 rtp	equ	0
 biosver	macro
-	db	"3.1.1-pre.131"
+	db	"3.1.1-pre.132"
 	endm