From ad8a347d7df08b9eb30ae97605e80eb2acbcc076 Mon Sep 17 00:00:00 2001
From: Nero <41307858+nero@users.noreply.github.com>
Date: Fri, 25 Oct 2019 13:09:53 +0000
Subject: [PATCH] bios8086: implement CHS disk i/o using int13h

---
 Makefile      |  5 +++
 bios/8086.asm | 98 ++++++++++++++++++++++++++++++++++++++++++++-------
 2 files changed, 91 insertions(+), 12 deletions(-)

diff --git a/Makefile b/Makefile
index be96c77..115d588 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,5 @@
 FLOPPY = 360
+BIOS = 0xFA00
 
 PROGRAMS = $(patsubst %.asm,%.com,$(wildcard com/*.asm))
 DISTFILES = rdos.bin $(PROGRAMS)
@@ -10,6 +11,7 @@ QEMU_ARGS = $(addprefix --option-rom ,$(ROMS))
 
 NASM = nasm
 NASM_ARGS = -s -Ilib -Plib/nasmcomp.asm -w-macro-params
+NASM_ARGS += -DBIOS=$(BIOS)
 
 EMUL = utils/emul
 
@@ -46,6 +48,9 @@ rom/%.rom: rom/%.asm
 com/%.com: com/%.asm
 	$(NASM) $(NASM_ARGS) -o $@ $<
 
+bios%.bin: bios/%.asm
+	$(NASM) $(NASM_ARGS) -o $@ $<
+
 fdimage.img: boot/fat.bs $(DISTFILES)
 	mformat -C -i $@ -f $(FLOPPY) -B boot/fat.bs ::
 	mcopy -i $@ $(DISTFILES) ::
diff --git a/bios/8086.asm b/bios/8086.asm
index c939e49..8921404 100644
--- a/bios/8086.asm
+++ b/bios/8086.asm
@@ -1,9 +1,8 @@
-ORG (RAM-0x600)
+ORG BIOS
 CPU 8086
 
 DISKCX: EQU 0x40
-DISKDL: EQU 0x42
-DISKDH: EQU 0x43
+DISKDX: EQU 0x42
 DISKBX: EQU 0x44
 
 JMP NEAR BOOT
@@ -22,10 +21,11 @@ JMP NEAR SETDMA
 JMP NEAR READ
 JMP NEAR WRITE
 JMP NEAR LISTST
-JMP NEAR SECTRAN
 
 BOOT:
-  STC
+  MOV AL, 0x19
+  CALL MSG
+  DB "BIOS 8086", 0
   RET
 
 WBOOT:
@@ -50,6 +50,44 @@ CONIN:
   JZ CONIN
   RET
 
+MSG:
+  POP SI
+.LOOP:
+  MOV DL, BYTE [SI]
+  INC SI
+  TEST DL, DL
+  JZ .END
+  CALL CONOUT
+  JMP .LOOP
+.END:
+  MOV DL, 0x20
+  CALL CONOUT
+  CALL PRINTAL
+  MOV DL, 0x0A
+  CALL CONOUT
+  MOV DL, 0x0D
+  CALL CONOUT
+  PUSH SI
+  RET
+
+PRINTAL:
+  PUSH AX
+  PUSH DX
+  AAM 16
+  MOV DL, AH
+  CALL PRINTNIB
+  MOV DL, AL
+  CALL PRINTNIB
+  POP DX
+  POP AX
+  RET
+
+PRINTNIB:
+  ADD DL, 0x30
+  CMP DL, 0x3a
+  JL CONOUT
+  ADD DL, 0x07
+
 CONOUT:
   PUSH AX
   PUSH BX
@@ -86,7 +124,7 @@ HOME:
   RET
 
 SELDSK:
-  MOV BYTE [DISKDL], CL
+  MOV BYTE [DISKDX], CL
   XOR BX, BX
   RET
 
@@ -102,7 +140,7 @@ SETTRK:
   XOR CH, CH
   RCR DX, 1
   RCL CH, 1
-  MOV BYTE [DISKDH], CH
+  MOV BYTE [DISKDX+1], CH
 
   ; DX is sector number now
   ; Shift into format for int13
@@ -122,7 +160,8 @@ SETTRK:
   RET
 
 SETSEC:
-  STC
+  AND WORD [DISKCX], 0xFFA0
+  OR BYTE [DISKCX], CL
   RET
 
 SETDMA:
@@ -130,13 +169,48 @@ SETDMA:
   RET
 
 READ:
-  STC
+  PUSH CX
+  PUSH DX
+  PUSH BX
+
+  MOV AX, 0x0201
+  MOV CX, [DISKCX]
+  MOV DX, [DISKDX]
+  MOV BX, [DISKBX]
+  INT 0x13
+  XCHG AH, AL
+
+  POP BX
+  POP DX
+  POP CX
+
+  JC DISKERR
   RET
 
 WRITE:
-  STC
+  PUSH CX
+  PUSH DX
+  PUSH BX
+
+  MOV AX, 0x0301
+  MOV CX, [DISKCX]
+  MOV DX, [DISKDX]
+  MOV BX, [DISKBX]
+  INT 0x13
+  XCHG AH, AL
+
+  POP BX
+  POP DX
+  POP CX
+
+  JC DISKERR
   RET
 
-SECTRAN:
-  STC
+DISKERR:
+  PUSHF
+  PUSH SI
+  CALL MSG
+  DB "DISKERR", 0
+  POP SI
+  POPF
   RET