From da882d26a5768c663010527b502490f8d325c7f8 Mon Sep 17 00:00:00 2001
From: b1ackmai1er <difficultylevelhigh@gmail.com>
Date: Sun, 1 Aug 2021 22:45:50 +0800
Subject: [PATCH] DMA fall-back mode for md.asm driver

---
 Source/HBIOS/dma.asm | 13 ++++++++++++-
 Source/HBIOS/md.asm  | 39 +++++++++++++++++++++++++++++++++------
 2 files changed, 45 insertions(+), 7 deletions(-)

diff --git a/Source/HBIOS/dma.asm b/Source/HBIOS/dma.asm
index 065c30e1..314a30b4 100644
--- a/Source/HBIOS/dma.asm
+++ b/Source/HBIOS/dma.asm
@@ -26,6 +26,8 @@ DMA_RESET			.equ	$c3
 ;DMA_ENABLE_AFTER_RETI		.equ	$b7
 ;DMA_REINIT_STATUS_BYTE		.equ	$8b
 ;
+DMA_FBACK			.equ	TRUE
+;
 ;==================================================================================================
 ; DMA INITIALIZATION CODE
 ;==================================================================================================
@@ -67,9 +69,18 @@ DMA_NOTFOUND:
 	push	af
 	call	PRTSTRD
 	.db	" NOT PRESENT$"
+
+#IF (DMA_FBACK)
+	call	PRTSTRD
+	.db	". USING SOFTWARE$"
+	LD	A,ERR_NOHW
+	LD	(DMA_FAIL_FLAG),A
+#ENDIF
 	pop	af
 	jr	DMA_EXIT
-
+;
+DMA_FAIL_FLAG:
+	.db	0	
 ;
 ;==================================================================================================
 ; DMA PROBE - WRITE TO ADDRESS REGISTER AND READ BACK
diff --git a/Source/HBIOS/md.asm b/Source/HBIOS/md.asm
index 06c5327b..88acda0f 100644
--- a/Source/HBIOS/md.asm
+++ b/Source/HBIOS/md.asm
@@ -359,14 +359,28 @@ MD_SECM:
 	LD	DE,(MD_DSKBUF)
 ;
 #IF (DMAENABLE & (DMAMODE=DMAMODE_ECB))
+#IF (DMA_FBACK)
+	LD	A,(DMA_FAIL_FLAG)
+	OR	A
+	JR	NZ,MD_NODMA
+#ENDIF
 	LD	BC,512-1		; COPY ONE 512B SECTOR FROM THE
-	CALL	DMALDIR			; 4K SECTOR TO THE DISK BUFFER
-#ELSE	
+	JP	DMALDIR			; 4K SECTOR TO THE DISK BUFFER
+#ENDIF
+MD_NODMA:
+#IF (!(DMAENABLE & (DMAMODE=DMAMODE_ECB)))	
+	LD	BC,512			; COPY ONE 512B SECTOR FROM THE
+	LDIR				; 4K SECTOR TO THE DISK BUFFER
+	XOR	A
+	RET
+#ELSE
+#IF  (DMA_FBACK)
 	LD	BC,512			; COPY ONE 512B SECTOR FROM THE
 	LDIR				; 4K SECTOR TO THE DISK BUFFER
 	XOR	A
-#ENDIF
 	RET
+#ENDIF
+#ENDIF
 ;
 ; SETUP DE:HL AS THE SECTOR ADDRESS TO READ OR WRITE
 ;
@@ -479,14 +493,27 @@ MD_SECM1:				; DESIRED SECTOR IS IN BUFFER
 ;
 	LD	HL,(MD_DSKBUF)
 #IF (DMAENABLE & (DMAMODE=DMAMODE_ECB))
+#IF (DMA_FBACK)
+	LD	A,(DMA_FAIL_FLAG)
+	OR	A
+	JR	NZ,MD_NODMA1
+#ENDIF
 	LD	BC,512-1		; COPY ONE 512B SECTOR FROM THE
 	CALL	DMALDIR			; THE DISK BUFFER TO 4K SECTOR
 	RET	NZ			; EXIT IF DMA COPY ERROR
-#ELSE
+	JR	MD_NODMAERR
+#ENDIF
+MD_NODMA1:
+#IF (!(DMAENABLE & (DMAMODE=DMAMODE_ECB)))
 	LD	BC,512			; COPY ONE 512B SECTOR FROM THE
-	LDIR				; THE DISK BUFFER TO 4K SECTOR
+	LDIR
+#ELSE
+#IF  (DMA_FBACK)			; THE DISK BUFFER TO 4K SECTOR
+	LD	BC,512
+	LDIR
 #ENDIF
-;
+#ENDIF
+MD_NODMAERR:
 	LD	IX,MD_F4KBUF		; SET SOURCE ADDRESS
 	LD	HL,MD_FWRIT_R		; PUT ROUTINE TO CALL
 	CALL	MD_FNCALL		; EXECUTE: WRITE 4K SECTOR