From eb67071ffb1f9c355de0543fbfa7848a0bc92ac5 Mon Sep 17 00:00:00 2001
From: Ain <41307858+nero@users.noreply.github.com>
Date: Sun, 24 Nov 2019 11:28:39 +0000
Subject: [PATCH] Ubuntu needs stdint.h for uint8_t

---
 boot/fat.asm        | 145 +++++++++++++++++++++++++++++++++++++++-----
 src/utils/fix-rom.c |   1 +
 2 files changed, 132 insertions(+), 14 deletions(-)

diff --git a/boot/fat.asm b/boot/fat.asm
index 9443bdb..71a2ab4 100644
--- a/boot/fat.asm
+++ b/boot/fat.asm
@@ -1,10 +1,18 @@
+; Memory layout:
 %define segment   0x00100
-%define self      (0x7C00-(segment<<4)) ; 1 sector
 
-cpu 8086
+%define self      (0x7C00-(segment<<4)) ; 1 sector
+%define fattab    (self+0x200) ; variable size
+%define rootdir   0x00100 ; variable size
+%define prog      0x0F000 ; 4K at the end for OS
+
 org self
+
 jmp short init
 
+cluster_offset:
+  dw 0
+
 times (0x0B - ($-$$)) db 0
 
 fdc:
@@ -57,16 +65,127 @@ main:
   ; Stack grows down from 64k
   mov ax, cs
   mov ss, ax
-  mov sp, BDOS
+  mov sp, prog
   mov ds, ax
   mov es, ax
 
   mov [fdc.drv], dl ; save drive number in fd
+  sti
 
-  mov ax, 1
-  mov cx, 8
-  mov dx, 0
-  mov bx, BDOS
+  ; load fat table into memory
+  mov ax, [fdc.rsc]
+  mov cx, [fdc.sf]
+  xor dx, dx
+  mov bx, fattab
+  call load_sectors
+
+  ; calculate length of rootdir
+  mov ax, [fdc.rde]
+  mov cl, 4
+  shr ax, cl ; 32 bytes per entry
+  mov cx, ax
+
+  ; load root dir
+  xor dx, dx
+  mov ax, [fdc.sf]
+  mul byte [fdc.fn]
+  add ax, [fdc.rsc]
+  mov bx, rootdir
+  call load_sectors
+
+  ; remember where we left off
+  ; clusters start after rootdir
+  mov [cluster_offset], ax
+
+  ; Load kernel
+  mov bx, prog
+  mov ax, kernel_name
+  call load_file
+  mov bp, 0x3332
+  jc error
+
+  mov dl, [fdc.drv]
+
+  ; jump into kernel
+  jmp segment:prog
+
+; Load a file into memory
+; IN	AX	pointer to 8.3 filename
+;	ES:BX	pointer to target area
+; OUT	CF	flag set if error
+;	DI	file size in bytes (<64K)
+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
+  xor di, di
+  stc
+  ret
+.read:
+  mov ax, [si+0x1A]
+  mov di, [si+0x1C]
+  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
+; in    dx:ax   sector number
+;       es:bx   buffer
+;	cx	number of sectors to read
+; out	dx:ax	next sector to read
+;	es:bx	next free buffer
+;	cx	zero
+load_sectors:
+  ; fail instantly if reading sectors > 16 bit
+  test dx, dx
+  mov bp, 0x3330
+  jnz error
 
 .loop:
   push ax
@@ -98,15 +217,10 @@ main:
 
   ; count up for next sector
   add bx, 0x0200
-  add ax, 1
-  adc dx, 0
+  inc ax
 
   loop .loop
-
-  mov dl, [fdc.drv]
-
-  ; jump into bios cold boot entry point
-  jmp segment:BIOS
+  ret
 
 error:
   mov ax, bp
@@ -119,6 +233,9 @@ error:
   int 0x16
   int 0x19
 
+kernel_name:
+  db "BDOS    BIN"
+
 times (0x1FE - ($-$$)) db 0
 
 dw 0xAA55
diff --git a/src/utils/fix-rom.c b/src/utils/fix-rom.c
index 05cfc83..d1099ed 100644
--- a/src/utils/fix-rom.c
+++ b/src/utils/fix-rom.c
@@ -3,6 +3,7 @@
 #include <sys/stat.h>
 #include <unistd.h>
 #include <stdlib.h>
+#include <stdint.h>
 
 struct stat sbuf;