From 7ba68e13f7d89454803599ce3ab8f6502cc2bc1f Mon Sep 17 00:00:00 2001
From: Ain <41307858+nero@users.noreply.github.com>
Date: Tue, 8 Oct 2019 19:53:41 +0000
Subject: [PATCH] Implement CP/M basic char io

---
 kernel/char.asm | 65 +++++++++++++++++++++++++++++++++++++++++++++++++
 kernel/fcb.asm  |  1 -
 kernel/main.asm | 49 +++++++++++++++----------------------
 3 files changed, 85 insertions(+), 30 deletions(-)
 create mode 100644 kernel/char.asm

diff --git a/kernel/char.asm b/kernel/char.asm
new file mode 100644
index 0000000..0e7d269
--- /dev/null
+++ b/kernel/char.asm
@@ -0,0 +1,65 @@
+console_input:
+  xor ax, ax
+  int 0x16
+  ; loop until we got >0
+  test al, al
+  jz console_input
+  push ax
+  push bx
+  jmp console_output.shortcut
+console_output:
+  push ax
+  push bx
+  mov al, dl
+.shortcut:
+  mov ah, 0x0e
+  xor bx, bx
+  int 0x10
+  pop bx
+  pop ax
+  ret
+
+print_string:
+  push si
+  mov si, dx
+.loop:
+  mov dl, BYTE [si]
+  cmp dl, '$'
+  jz .end
+  call console_output
+  inc si
+  jmp .loop
+.end:
+  pop si
+  ret
+
+read_buffer:
+  push bx
+  push si
+  xor bx, bx
+  mov si, dx
+.loop:
+  call console_input
+  cmp al, 0x0D
+  je .end
+  cmp al, 8
+  je .bs
+  mov [si+bx+2], al
+  inc bx
+  cmp bl, [si]
+  jc .loop
+.end:
+  mov byte [si+bx+2], 0x0D
+  mov [si+1], bl
+  pop si
+  pop bx
+  ret
+.bs:
+  test bx, bx
+  jz .loop
+  mov dl, 0x20
+  call console_output
+  mov dl, 8
+  call console_output
+  dec bx
+  jmp .loop
diff --git a/kernel/fcb.asm b/kernel/fcb.asm
index ddc6185..b17064d 100644
--- a/kernel/fcb.asm
+++ b/kernel/fcb.asm
@@ -24,7 +24,6 @@ fcb_open_rootdir:
   cmp byte [bx], 0
   jne .drivedone
   mov al, default_drive
-  inc al
   mov [bx], al
 .drivedone:
   mov dl, [bx]
diff --git a/kernel/main.asm b/kernel/main.asm
index 648c02c..83a0e6c 100644
--- a/kernel/main.asm
+++ b/kernel/main.asm
@@ -19,28 +19,20 @@ org self
 jmp init
 
 banner:
-  db "RDOS 2019-09", 0x0A, 0x0D, 0
-
-print_banner:
-  mov cl, 2
-  mov si, banner
-.loop:
-  mov dl, BYTE [si]
-  test dl, dl
-  jz .end
-  call cpm_syscall
-  inc si
-  jmp .loop
-.end:
-  ret
+  db "RDOS 2019-09", 0x0A, 0x0D, '$', 0
 
 init:
   mov sp, stack
+  mov default_drive, 0x01
 
-  call print_banner
+  mov dx, banner
+  call print_string
 
-  mov si, init_program
-  call exec
+  mov dx, 0x79
+  mov byte [0x79], 0x7F
+  call read_buffer
+  mov ax, [0x79]
+  int3
 
   cli
 .halt:
@@ -51,21 +43,20 @@ init_program:
   db "HELLO.COM", 0
 
 cpm_syscall:
-  cmp cl, 0x02
-  je putc
+  cmp cl, 0
+  je init
+  cmp cl, 1
+  je console_input
+  cmp cl, 2
+  je console_output
+  cmp cl, 9
+  je print_string
+  cmp cl, 10
+  je read_buffer
   stc
   ret
 
-putc:
-  push ax
-  push bx
-  mov al, dl
-  mov ah, 0x0e
-  mov bx, 0x0000
-  int 0x10
-  pop bx
-  pop ax
-  ret
+%include "char.asm"
 
 %include "exec.asm"
 %include "fcb.asm"