From df4d3a90e3e5f60d4dba9f40234e7dc1448d064b Mon Sep 17 00:00:00 2001
From: Ain <41307858+nero@users.noreply.github.com>
Date: Mon, 23 Sep 2019 22:05:01 +0000
Subject: [PATCH] Use SYS extension for kernel

---
 .gitignore   |   1 +
 Makefile     |   6 +--
 boot/fat.asm | 140 +++++++++++++++++++++++----------------------------
 3 files changed, 68 insertions(+), 79 deletions(-)

diff --git a/.gitignore b/.gitignore
index 6093e0f..10f9118 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,3 +6,4 @@
 *.lst
 *.exe
 *.log
+*.sys
diff --git a/Makefile b/Makefile
index 1446b3b..708b11c 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,7 @@
 FLOPPY = 360
 
 PROGRAMS = $(patsubst %.asm,%.com,$(wildcard programs/*.asm))
-DISTFILES = kernel.com $(PROGRAMS)
+DISTFILES = rdos.sys $(PROGRAMS)
 ROMS =
 
 QEMU_ARCH = $(shell uname -m)
@@ -23,9 +23,9 @@ endif
 
 .PHONY: default clean qemu-rom qemu-floppy
 
-default: kernel.rom
+default: rdos.sys
 
-kernel.com: kernel/*.asm lib/*.asm
+rdos.sys: kernel/*.asm lib/*.asm
 	nasm -s -o $@ -l kernel.lst -I lib -I kernel kernel/main.asm
 
 debug.rom: debug/*.asm lib/*.asm
diff --git a/boot/fat.asm b/boot/fat.asm
index cc1a26d..db57653 100644
--- a/boot/fat.asm
+++ b/boot/fat.asm
@@ -107,19 +107,11 @@ main:
   ; clusters start after rootdir
   mov [cluster_offset], ax
 
+  mov ax, filename
   call load_file
   mov bp, 0x3332
   jc error
 
-  ; setup int 19h call if prog returns
-  mov WORD [psp], 0x19CD
-
-  ; clean registers
-  xor ax, ax
-  xor cx, cx
-  xor dx, dx
-  xor bx, bx
-
   ; restore boot drive number
   mov dl, [fdc.drv]
 
@@ -132,6 +124,68 @@ main:
   ; jump into target
   jmp 0x07B0:0x0100
 
+; Load a file into memory
+; IN	AX	pointer to 8.3 filename
+;	ES:BX	pointer to target area
+; OUT	CF	flag set if error
+load_file:
+  mov si, rootdir
+  mov cx, [fdc.rde]
+.search:
+  push cx
+  push si
+  mov di, ax
+  mov cx, 11
+  repe cmpsb
+  pop si
+  pop cx
+  je .read
+  add si, 0x20
+  loop .search
+  stc
+  ret
+.read:
+  add si, 0x1A
+  lodsw
+  mov bx, prog
+  jmp read_clusters
+
+; Read the file given by cluster number
+; into the target program area
+; in	ax	cluster number
+read_clusters:
+  ; read cluster into area for target file
+  push ax
+  sub ax, 2
+  mul BYTE [fdc.sc]
+  add ax, [cluster_offset]
+  xor dx, dx
+  mov cx, [fdc.sc]
+  xor ch, ch
+  call load_sectors
+  pop ax
+
+  ; calculate index in FAT
+  mov si, ax
+  shr si, 1
+  add si, ax
+  add si, fattab
+
+  ; load entry from FAT, truncate to 12 bit
+  mov dx, [si]
+  test ax, 1
+  jz .noshift
+  mov cl, 4
+  shr dx, 4
+.noshift:
+  mov ax, dx
+
+  and ax, 0x0FFF
+  cmp ax, 0x0FF8
+  jc read_clusters
+
+  ret
+
 ; Read sectors from disk
 ; Does not return on error
 ; ax and bx will be incremented, cx decremented
@@ -182,72 +236,6 @@ load_sectors:
   loop .loop
   ret
 
-; Load the file in [filename]
-; or exit with carry set
-load_file:
-  mov si, rootdir
-  mov cx, [fdc.rde]
-.loop:
-  call file_match
-  je read_clusters
-  add si, 0x20
-  loop .loop
-  stc
-  ret
-
-; Compares the FAT dirent against [filename]
-; in	ds:si	filename
-; out	ZF	zero flag set if equal
-file_match:
-  push cx
-  push si
-  mov di, filename
-  mov cx, 11
-  repe cmpsb
-  pop si
-  pop cx
-  ret
-
-; Read the file given by cluster number
-; into the target program area
-; in	ax	cluster number
-read_clusters:
-  add si, 0x1A
-  lodsw
-  mov bx, prog
-.loop:
-  ; read cluster into area for target file
-  push ax
-  sub ax, 2
-  mul BYTE [fdc.sc]
-  add ax, [cluster_offset]
-  xor dx, dx
-  mov cx, [fdc.sc]
-  xor ch, ch
-  call load_sectors
-  pop ax
-
-  ; calculate index in FAT
-  mov si, ax
-  shr si, 1
-  add si, ax
-  add si, fattab
-
-  ; load entry from FAT, truncate to 12 bit
-  mov dx, [si]
-  test ax, 1
-  jz .noshift
-  mov cl, 4
-  shr dx, 4
-.noshift:
-  mov ax, dx
-
-  and ax, 0x0FFF
-  cmp ax, 0x0FF8
-  jc .loop
-
-  ret
-
 error:
   mov ax, bp
   mov ah, 0x0e
@@ -260,7 +248,7 @@ error:
   int 0x19
 
 filename:
-  db "KERNEL  COM"
+  db "RDOS    SYS"
 
 times (0x1FE - ($-$$)) db 0