cbios: it is the DPB that can be dynamic, not the DPH

BDOS gets really unhappy about a shared DPH

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 26 insertions, 27 deletions

diff --git a/data/cbios.asm b/data/cbios.asm
index 77746ae..b6c7b12 100644
--- a/data/cbios.asm
+++ b/data/cbios.asm
@@ -48,17 +48,28 @@ v24vec:		defw irq_v24
 	
 ; disk parameter header (16 bytes for each drive),
 ; the chk and alv get dynamically adjusted
-dpbase:
+alvsize:	equ 120
+dpm:		macro ndisk
 		dw 0            ; sector translation table (0 = no translation)
 		dw 0            ; must be 0
 		dw 0            ; must be 0
 		dw 0            ; must be 0
 		dw dirbf        ; DIRBUF (address of shared 128 byte scratch pad area)
 		dw dpblk        ; DPB (disk parameter block)
-dp_csv:		dw csv          ; CSV (unique scratch pad used to check for changed disks)
-dp_alv:		dw alv          ; ALV (unique scratch pad for allocation information)
+		dw csv          ; CSV (unique scratch pad used to check for changed disks)
+		dw alv+alvsize*ndisk	; ALV (unique scratch pad for allocation information)
+		endm
 
-ndisks:     equ 8           ; number of disks we defined
+dpbase:
+		dpm 0
+		dpm 1
+		dpm 2
+		dpm 3
+		dpm 4
+		dpm 5
+		dpm 6
+		dpm 7
+ndisks:		equ 8           ; number of disks we defined
 
 ; disk parameter block (can be shared by all disks with same configuration)
 ; each volue is 15,597,568 bytes (238*256*256), which is too much for
@@ -414,6 +425,7 @@ reader:		; read character from reader device (which we don't have)
 
 seldsk:		; select disk indicated by register C
 		ld hl, 0    ; return code 0 indicates error
+		ld b,h	    ; = 0
             	ld a, c
             	cp ndisks
             	ret nc      ; return (with error code) if C >= ndisks ie illegal drive
@@ -425,15 +437,14 @@ seldsk:		; select disk indicated by register C
 		ld a,119
 sd1:		ld (curxtrk), a	; store track offset (+119 for odd volume)
             	; compute proper disk parameter header address in HL
-
-		; Each allocation vector is 120 bytes long
-		ld a,120
-		ld e,c
-		ld d,h		; = 0
-		ld hl,alv
-		call multiply_add
-		ld (dp_alv),hl
+		ld a,c
+		add a
+		add a
+		add a
+		add a
+		ld c,a
 		ld hl,dpbase
+		add hl,bc
 		ret
 
 home:		ld bc, 0
@@ -532,18 +543,6 @@ sc_wait_ok:
 		ret c
 		jr sc_wait_ok
 
-multiply_add:	; HL <- HL + DE * A, trashes B
-		ld b,8
-m1:
-		rrca
-		jr nc,m2
-		add hl,de
-m2:
-		sla e
-		rl d
-		djnz m1
-		ret
-
 bootmsg:	db "CP/M BIOS (H. Peter Anvin, 2014-06-01)\r\n"
 		db "CP/M 2.2 Copyright 1979 (c) by Digital Research\r\n"
 zero:
@@ -560,6 +559,6 @@ curdmaaddr:	dw 0
 conflag:	db 0
 
 ; scratch RAM used by BDOS
-dirbf:      ds 128           ; directory scratch area
-alv:        ds 120*ndisks    ; allocation vectors, each (DSM/8)+1 byte
-csv:        ds 0*ndisks      ; check vectors, each CKS bytes
+dirbf:      ds 128               ; directory scratch area
+alv:        ds alvsize*ndisks    ; allocation vectors, each (DSM/8)+1 byte
+csv:        ds 0*ndisks          ; check vectors, each CKS bytes