From 74f9daaaaab37fe1281271ba06b47789dc2a4e5f Mon Sep 17 00:00:00 2001
From: Wayne Warthen <wwarthen@gmail.com>
Date: Mon, 21 Jul 2025 11:19:42 -0700
Subject: [PATCH] USB Floppy Geometry Fix, Issue #456

USB Floppy Driver modified to:

- return media id for 1.44 MB Floppy (MID_FD144)
- translate CHS to LBA

At present, floppy media is assumed to be high density 1.44MB.
---
 Source/HBIOS/ch376ufi.asm | 42 +++++++++++++++++++++++++++++++++++++--
 Source/ver.inc            |  2 +-
 Source/ver.lib            |  2 +-
 3 files changed, 42 insertions(+), 4 deletions(-)

diff --git a/Source/HBIOS/ch376ufi.asm b/Source/HBIOS/ch376ufi.asm
index ab2e18fb..e0eefbd6 100644
--- a/Source/HBIOS/ch376ufi.asm
+++ b/Source/HBIOS/ch376ufi.asm
@@ -69,7 +69,7 @@ CH_UFI_SEEK:
 	EXX
 
 	BIT	7,D			; CHECK FOR LBA FLAG
-	CALL	Z,HB_CHS2LBA		; CLEAR MEANS CHS, CONVERT TO LBA
+	CALL	Z,CH_UFI_CHS2LBA	; CLEAR MEANS CHS, CONVERT TO LBA
 	RES	7,D			; CLEAR FLAG REGARDLESS (DOES NO HARM IF ALREADY LBA)
 
 	PUSH	DE
@@ -83,6 +83,44 @@ CH_UFI_SEEK:
 	XOR	A
 	RET
 ;
+; Helper function to convert CHS address in DE:HL to LBA.
+; Currently assumes 1.44MB floppy media
+; LBA = (TRACK * #HDS * #SPT) + (HEAD * #SPT)  + SECTOR
+; For 1.44MB FLOPPY, #HDS = 2, #SPT = 18
+; LBA = (TRACK * 36) + (HEAD * 18) + SECTOR
+; Algorithm uses B=#HDS*SPT, C=#SPT.  For now, hard coded B=36, C=18
+; for 1.44MB media.  In future, BC could be passed in to accommodate
+; different media geometry.
+;
+CH_UFI_CHS2LBA:
+	LD	B,2 * 18		; #HDS * #SPT (SECTORS PER CYLINDER)
+	LD	C,18			; #SPT
+
+	; TRACK * #HDS * #SPT
+	PUSH	DE			; SAVE DE
+	LD	E,B			; SECTORS PER CYLINDER
+	LD	H,L			; LSB OF TRACK TO H, H IS NEVER USED BY FLOPPY CHS
+	CALL	MULT8			; HL = H * E; TRACK LBA
+	POP	DE			; RECOVER DE
+	PUSH	HL			; SAVE TRACK LBA
+	
+	; HEAD * #SPT
+	PUSH	DE			; SAVE DE
+	LD	E,C			; SECTORS PER TRACK
+	LD	H,D			; HEADS
+	CALL	MULT8			; HL = H * E; HEAD LBA
+	POP	DE			; RECOVER DE
+
+	; COMPUTE LBA (HL) = SECTOR (E) + HEAD LBA (HL) + TRACK LBA (TOS)
+	LD	A,E			; SECTOR
+	CALL	ADDHLA			; SECTOR * HEAD LBA
+	POP	DE			; RECOVER TRACK LBA
+	ADD	HL,DE			; ADD IN TRACK LBA
+
+	; FINISH UP
+	LD	DE,0			; DE IS ALWAYS ZERO
+	RET
+;
 ; ### Function 0x13 -- Disk Read (DIOREAD)
 ;
 ; Inputs
@@ -233,7 +271,7 @@ CH_UFI_DEVICE:
 ; function will return an error status.
 ;
 CH_UFI_MEDIA:
-	LD	E, MID_MDRAM	;todo verify device still active?
+	LD	E, MID_FD144	;todo verify device still active?
 	XOR	A
 	RET
 
diff --git a/Source/ver.inc b/Source/ver.inc
index f9ae15d7..4508e6f8 100644
--- a/Source/ver.inc
+++ b/Source/ver.inc
@@ -2,7 +2,7 @@
 #DEFINE	RMN	6
 #DEFINE	RUP	0
 #DEFINE	RTP	0
-#DEFINE BIOSVER	"3.6.0-dev.13"
+#DEFINE BIOSVER	"3.6.0-dev.14"
 #define rmj	RMJ
 #define rmn	RMN
 #define rup	RUP
diff --git a/Source/ver.lib b/Source/ver.lib
index ffa3b38f..c0841e56 100644
--- a/Source/ver.lib
+++ b/Source/ver.lib
@@ -3,5 +3,5 @@ rmn	equ	6
 rup	equ	0
 rtp	equ	0
 biosver	macro
-	db	"3.6.0-dev.13"
+	db	"3.6.0-dev.14"
 	endm