mikeOS/doc/handbook-appdev-asm.html at master · mboukhalfa/mikeOS · GitHub

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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">

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<title>The MikeOS Assembly App Developer Handbook</title>

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<table border="0" cellpadding="10">
<tr>


<!-- NAVIGATION PANEL -->

<td style="border:1px solid black; width:160px;" valign="top">

<h3>Navigate</h3>

<p><strong>Overview</strong></p>
<ul>
<li><a href="#introduction">Introduction</a></li>
<li><a href="#toolsneeded">Tools needed</a></li>
</ul>

<p><strong>Example</strong></p>
<ul>
<li><a href="#sourcecode">Source code</a></li>
<li><a href="#building">Building</a></li>
<li><a href="#explanation">Explanation</a></li>
</ul>

<p><strong>System calls</strong></p>
<ul>
<li><a href="#syscallintro">Introduction</a></li>
<li><a href="#syscalldisk">Disk</a></li>
<li><a href="#syscallkeyboard">Keyboard</a></li>
<li><a href="#syscallmath">Math</a></li>
<li><a href="#syscallmisc">Misc</a></li>
<li><a href="#syscallports">Ports</a></li>
<li><a href="#syscallscreen">Screen</a></li>
<li><a href="#syscallstring">String</a></li>
<li><a href="#syscallsound">Sound</a></li>
<li><a href="#syscallbasic">BASIC</a></li>
</ul>

<p><strong>Extra</strong></p>
<ul>
<li><a href="#help">Help</a></li>
<li><a href="#license">License</a></li>
</ul>

</td>


<!-- MAIN CONTENT PANEL -->

<td valign="top">

<h1>The MikeOS Assembly App Developer Handbook</h1>

<h3>For version 4.5, 21 December 2014 - (C) MikeOS Developers</h3>

<p>This documentation file explains how write software for MikeOS in assembly language. It shows you the tools you need,
how MikeOS programs work, and how to use the system calls included in the kernel. If you have
any questions, see <a href="http://mikeos.berlios.de">the MikeOS website</a> for contact details
and mailing list information.</p>

<p>Click the links on the left to navigate around this guide.</p>

<br />


<hr noshade="noshade" />


<h2>Overview</h2>

<a name="introduction"></a>
<h3>Introduction</h3>

<p>Many MikeOS programs are written in 16-bit, real mode assembly language. (The OS
also includes a BASIC interpreter.) Because MikeOS and its programs live in a single 64K
memory segment, you do not need to concern yourself with segment registers.</p>

<p>MikeOS programs are loaded at the <strong>32K point</strong> (32768) in the segment, and have a
maximum size of 32K. Consequently, your programs will need to begin with these directives:</p>

<pre>
BITS 16
ORG 32768
</pre>

<p>There are many system calls available in MikeOS for controlling the screen, getting input, manipulating
strings, loading/saving files, and more. All parameters to MikeOS system calls are passed in registers,
and not on the stack. To use them in your programs, you need this line:</p>

<pre>
%INCLUDE "mikedev.inc"
</pre>

<p>This doesn't include any code, but a list of <strong>equ</strong> directives that point to system call vectors
in the kernel. So, by including this file you can call, for instance, the MikeOS <strong>os_print_string</strong>
routine without having to know exactly where it is in the kernel. <strong>mikedev.inc</strong> is included in
the <strong>programs/</strong> directory of the MikeOS download -- it also provides a quick reference to the
system calls.</p>

<p>If a MikeOS program is run from the command line, and one or more parameters was provided with the command,
they are passed to the program via the SI register as a zero-terminated string.</p>


<br />


<a name="toolsneeded"></a>
<h3>Tools needed</h3>

<p>To write MikeOS programs you need:</p>

<ul>
<li><strong>NASM</strong> -- A powerful, free and open source assembler</li>
<li><strong>mikedev.inc</strong> -- The system call vectors described above</li>
<li>A way to add programs to the floppy disk</li>
</ul>

<p>Let's clarify this: MikeOS uses NASM for its programs and kernel source code, hence why we recommend it
here. You can, of course, use any other assembler that can output plain binary files (ie with no header)
and accept 16-bit code. NASM is available in most Linux distro repositories, or you can download the Windows
version <a href="http://www.nasm.us/pub/nasm/releasebuilds/">from here</a> (get the 'win32' file).</p>

<p>For the second point, copy <strong>programs/mikedev.inc</strong> so that it's alongside your program's
source code for inclusion.</p>

<p>For the third point, if you've written MikeOS to a real floppy disk, you can just copy your <strong>.BIN</strong>
programs onto that disk (root directory only!), boot MikeOS and test them out. If you're working with the virtual
<strong>mikeos.flp</strong> disk image, see the <em>Copying files</em> section of the User Handbook.</p>


<br />


<hr noshade="noshade" />


<h2>Example</h2>

<a name="sourcecode"></a>
<h3>Source code</h3>

<p>Here is an example MikeOS program, in NASM format, which prints a string to the screen
and waits for the user to press a key before finishing:</p>

<pre>
	BITS 16
	ORG 32768
	%INCLUDE 'mikedev.inc'

start:
	mov si, mystring
	call os_print_string

	call os_wait_for_key

	ret

	mystring db 'My first MikeOS program!', 0
</pre>


<br />


<a name="building"></a>
<h3>Building</h3>

<p>Save the above code as <strong>testapp.asm</strong>, and enter this command to assemble it
(works on both Linux and Windows):</p>

<pre>
nasm -f bin -o testapp.bin testapp.asm
</pre>

<p>Using the '-f bin' option we tell NASM that we just want a plain binary file: no header or sections.
The resulting executable file is <strong>testapp.bin</strong> that we can copy to our floppy disk or add
to the virtual disk image as described in <em>Copying files</em> in the User Handbook. Then we can boot
MikeOS and run the program.</p>


<br />


<a name="explanation"></a>
<h3>Explanation</h3>


<p>This is a very short program, but we'll explain exactly how it works for complete clarity. The first
three lines will not be assembled to machine code instructions, but are just directives to tell NASM that
we want to operate in 16 bit mode, our code is written to be executed from the 32K mark, and we want to
use system calls from the MikeOS API.</p>

<p>Next we have the 'start:' label, which is not essential but good practice to make things clear. We put
the location of a zero-terminated string into the <strong>SI</strong> register, then call the MikeOS
<strong>os_print_string</strong> routine which we can access via the vectors listed in <strong>mikedev.inc</strong>.
After that we pause program until a the user presses a key.</p>

<p>All MikeOS programs must end with a <strong>ret</strong> instruction, which passes control back to the OS.
After that instruction we have the data for our string. And that's it!</p>


<br />


<hr noshade="noshade" />


<h2>System calls</h2>

<a name="syscallintro"></a>
<h3>Introduction</h3>

<p>The MikeOS kernel includes system calls for outputting to the screen, taking keyboard input,
manipulating strings, producing PC speaker sounds, math operations and disk I/O. You can get
a quick reference to the registers that these calls take and pass back by looking at <strong>mikedev.inc</strong>,
and see practical use of the calls in the <strong>programs/</strong> directory.</p>

<p>Here we have a detailed API explanation with examples. You can see the full source code behind these system
calls in the <strong>source/features/</strong> directory in MikeOS. Each aspect of the API below is contained
within an assembly source file, so you can enhance the system calls as per the MikeOS System Developer Handbook.</p>


<br />


<hr style="width:50%;" />


<a name="syscalldisk"></a>
<h2>Disk</h2>


<h3>os_get_file_list</h3>
<p><strong>Generate comma-separated string of files on floppy</strong></p>

<ul>
 <li>IN/OUT: AX = location to store zero-terminated filename string</li>
</ul>

<p>Example:</p>

<pre>
	mov ax, .filestring
	call os_get_file_list

	; Now .filestring will contain something like
	; 'HELLO.BIN,FOO.BAR,THREE.TXT', 0

	.filestring	times 256 db 0
</pre>


<br />


<h3>os_load_file</h3>
<p><strong>Load file into RAM</strong></p>

<ul>
 <li>IN: AX = location of zero-terminated filename string, CX = location in RAM to load file</li>
 <li>OUT: BX = file size (in bytes), carry set if file not found</li>
</ul>

<p>Example:</p>

<pre>
	mov ax, filename
	mov cx, 36960		; 4K after where external program loads
	call os_load_file

	...

	filename db 'README.TXT', 0
</pre>

<br />


<h3>os_write_file</h3>
<p><strong>Save (max 64K) file to disk</strong></p>

<ul>
 <li>IN: AX = filename, BX = data location, CX = bytes to write</li>
 <li>OUT: Carry clear if OK, set if failure</li>
</ul>

<p>Example:</p>

<pre>
	; For this example, there's some text stored in .data

	mov ax, .filename
	mov bx, .data
	mov cx, 4192
	call os_write_file

	.filename	db 'HELLO.TXT', 0
	.data		times 4192 db 0
</pre>

<br />


<h3>os_file_exists</h3>
<p><strong>Check for presence of file on the floppy</strong></p>

<ul>
 <li>IN: AX = filename location</li>
 <li>OUT: carry clear if found, set if not</li>
</ul>

<p>Example:</p>

<pre>
	mov ax, .filename
	call os_file_exists
	jc .not_found

	...

.not_found:
	; Print error message here

	.filename	db 'HELLO.TXT', 0
</pre>


<br />


<h3>os_create_file</h3>
<p><strong>Creates a new 0-byte file on the floppy disk</strong></p>

<ul>
 <li>IN: AX = location of filename</li>
 <li>OUT: Nothing</li>
</ul>

<p>Example:</p>

<pre>
	mov ax, .filename
	call os_create_file

	...

	.filename	db 'HELLO.TXT', 0
</pre>


<br />


<h3>os_remove_file</h3>
<p><strong>Deletes the specified file from the filesystem</strong></p>

<ul>
 <li>IN: AX = location of filename to remove</li>
 <li>OUT: Nothing</li>
</ul>


<br />


<h3>os_rename_file</h3>
<p><strong>Change the name of a file on the disk</strong></p>

<ul>
 <li>IN: AX = filename to change, BX = new filename (zero-terminated strings)</li>
 <li>OUT: carry set on error</li>
</ul>

<p>Example:</p>

<pre>
	mov ax, .filename1
	mov bx, .filename2
	call os_rename_file

	jc .error

	...

.error:
	; File couldn't be renamed (may already exist)

	.filename1	db 'ORIG.TXT', 0
	.filename2	db 'NEW.TXT', 0
</pre>

<br />


<h3>os_get_file_size</h3>
<p><strong>Get file size information for specified file</strong></p>

<ul>
 <li>IN: AX = filename</li>
 <li>OUT: BX = file size in bytes (up to 64K) or carry set if file not found</li>
</ul>


<br />


<hr style="width:50%;" />


<a name="syscallkeyboard"></a>
<h2>Keyboard</h2>

<h3>os_wait_for_key</h3>
<p><strong>Waits for keypress and returns key</strong></p>

<ul>
 <li>IN: Nothing</li>
 <li>OUT: AX = key pressed, other regs preserved</li>
</ul>

<p>Example:</p>

<pre>
.loop:
	call os_wait_for_key
	cmp al, 'y'
	je .yes
	cmp al, 'n'
	je .no
	jmp .loop
</pre>

<br />


<h3>os_check_for_key</h3>
<p><strong>Scans keyboard for input, but doesn't wait</strong></p>

<ul>
 <li>IN: Nothing</li>
 <li>OUT: AX = 0 if no key pressed, otherwise scan code</li>
</ul>

<p>Example: see code above</p>


<br />


<hr style="width:50%;" />


<a name="syscallmath"></a>
<h2>Math</h2>

<h3>os_bcd_to_int</h3>
<p><strong>Converts binary coded decimal number to an integer</strong></p>

<ul>
 <li>IN: AL = BCD number</li>
 <li>OUT: AX = integer value</li>
</ul>

<p>Example:</p>

<pre>
	mov al, 00010110b	; 0001 0110 = 16 (decimal) or 10h in BCD
	call os_bcd_to_int

	; AX now contains the 16 bit-integer 00000000 00010000b
</pre>


<br />


<h3>os_long_int_negate</h3>
<p><strong>Multiply value in DX:AX by -1</strong></p>

<ul>
 <li>IN: DX:AX = long integer </li>
 <li>OUT: DX:AX = -(initial DX:AX)</li>
</ul>

<p>Example:</p>

<pre>
	mov dx, 01h
	mov ax, 45h
	call os_long_int_negate

	; DX now contains 0xFFFF
	; and AX 0xFEBB
</pre>

<br />


<h3>os_get_random</h3>
<p><strong>Get a random integer between high and low values (inclusive)</strong></p>

<ul>
 <li>IN: AX = low integer, BX = high</li>
 <li>OUT: CX = random number between AX and BX</li>
</ul>

<br />


<hr style="width:50%;" />


<a name="syscallmisc"></a>
<h2>Misc</h2>


<h3>os_get_api_version</h3>
<p><strong>Return current version of MikeOS API</strong></p>

<ul>
 <li>IN: Nothing </li>
 <li>OUT: AL = API version number</li>
</ul>

<p>Example:</p>

<pre>
	call os_get_api_version
	; AL now contains version number (eg 8)
</pre>


<br />


<h3>os_pause</h3>
<p><strong>Delay execution for specified 10ths of second</strong></p>

<ul>
 <li>IN: AX = number of 10ths of second to wait</li>
 <li>OUT: nothing</li>
</ul>

<p>Example:</p>

<pre>
	; Halt execution for 3 secs

	mov ax, 30
	call os_pause
</pre>


<br />


<h3>os_fatal_error</h3>
<p><strong>Display error message and halt execution</strong></p>

<ul>
 <li>IN: AX = error message string location</li>
 <li>OUT: nothing</li>
</ul>

<p>Example:</p>

<pre>
	mov ax, .error_msg
	call os_fatal_error

	.error_msg	db 'Massive error!', 0
</pre>


<br />


<hr style="width:50%;" />


<a name="syscallports"></a>
<h2>Ports</h2>


<h3>os_port_byte_out</h3>
<p><strong>Sends a byte to the specified port</strong></p>

<ul>
 <li>IN: DX = port address, AL = byte</li>
 <li>OUT: Nothing</li>
</ul>


<br />


<h3>os_port_byte_in</h3>
<p><strong>Retrieves a byte from the specified port</strong></p>

<ul>
 <li>IN: DX = port address</li>
 <li>OUT: AL = byte</li>
</ul>


<br />


<h3>os_serial_port_enable</h3>
<p><strong>Turn on the first serial port</strong></p>

<ul>
 <li>IN: AX = 0 for normal mode (9600 baud), or 1 for slow mode (1200 baud)</li>
 <li>OUT: AH = bit 7 clear on success</li>
</ul>


<br />


<h3>os_send_via_serial</h3>
<p><strong>Send a byte via the serial port</strong></p>

<ul>
 <li>IN: AL = byte to send via serial</li>
 <li>OUT: AH = bit 7 clear on success</li>
</ul>

<p>Example:</p>

<pre>
	mov al, 'a'			; Place char to transmit in AL
	call os_send_via_serial
	cmp ah, 128			; If bit 7 is set, there's an error
	jnz all_ok			; Otherwise it's all OK
	jmp oops_error			; Deal with the error
</pre>


<br />


<h3>os_get_via_serial</h3>
<p><strong>Get a byte from the serial port</strong></p>

<ul>
 <li>IN: nothing</li>
 <li>OUT: AL = byte that was received; OUT: AH = bit 7 clear on success</li>
</ul>

<p>Example:</p>

<pre>
	call os_get_via_serial
	cmp ah, 128		; If bit 7 is set, there's an error.
	jnz all_ok		; Otherwise it's all OK
	jmp oops_error		; Deal with the error

all_ok:
	mov [rx_byte], al	; Store byte we retrieved
</pre>

<br />


<hr style="width:50%;" />


<a name="syscallscreen"></a>
<h2>Screen</h2>


<h3>os_print_string</h3>
<p><strong>Displays text</strong></p>

<ul>
 <li>IN: SI = message location (zero-terminated string)</li>
 <li>OUT: Nothing (registers preserved)</li>
</ul>

<p>Example:</p>

<pre>
	mov si, .message
	call os_print_string

	...

	.message	db 'Hello, world', 0
</pre>

<br />


<h3>os_clear_screen</h3>
<p><strong>Clears the screen to background</strong></p>

<ul>
 <li>IN/OUT: Nothing (registers preserved)</li>
</ul>


<br />


<h3>os_move_cursor</h3>
<p><strong>Moves cursor in text mode</strong></p>

<ul>
 <li>IN: DH, DL = row, column </li>
 <li>OUT: Nothing (registers preserved)</li>
</ul>

<p>Example:</p>

<pre>
	; Move to middle of screen

	mov dh, 12
	mov dl, 40
	call os_move_cursor
</pre>


<br />


<h3>os_get_cursor_pos</h3>
<p><strong>Return position of text cursor</strong></p>

<ul>
 <li>OUT: DH, DL = row, column</li>
</ul>


<br />


<h3>os_print_horiz_line</h3>
<p><strong>Draw a horizontal line on the screen</strong></p>

<ul>
 <li>IN: AX = line type (1 for double, otherwise single)</li>
 <li>OUT: Nothing (registers preserved)</li>
</ul>


<br />


<h3>os_show_cursor</h3>
<p><strong>Turns on cursor in text mode</strong></p>

<ul>
 <li>IN/OUT: Nothing</li>
</ul>


<br />


<h3>os_hide_cursor</h3>
<p><strong>Turns off cursor in text mode</strong></p>

<ul>
 <li>IN/OUT: Nothing</li>
</ul>


<br />


<h3>os_draw_block</h3>
<p><strong>Render block of specified colour</strong></p>

<ul>
 <li>IN: BL/DL/DH/SI/DI = colour/start X pos/start Y pos/width/finish Y pos</li>
 <li>OUT: Nothing</li>
</ul>

<p>Example:</p>

<pre>
	mov bl, 0100111b	; White on red
	mov dl, 20		; Start X position
	mov dh, 2		; Start Y position
	mov si, 40		; Width
	mov di, 23		; Finish Y position
	call os_draw_block
</pre>


<br />


<h3>os_file_selector</h3>
<p><strong>Show a file selection dialog</strong></p>

<ul>
 <li>IN: Nothing </li>
 <li>OUT: AX = location of filename string (or carry set if Esc pressed)</li>
</ul>

<p>Example:</p>

<pre>
	call os_file_selector
	jc .esc_pressed

	; Now AX points to the chosen filename
	...

.esc_pressed:
	...
</pre>


<br />


<h3>os_list_dialog</h3>
<p><strong>Show a dialog with a list of options</strong></p>

<ul>
 <li>IN: AX = comma-separated list of strings to show (zero-terminated),</li>
 <li>&nbsp;BX = first help string, CX = second help string</li>
 <li>OUT: AX = number (starts from 1) of entry selected carry set if Esc pressed</li>
</ul>

<p>Example:</p>

<pre>
	mov ax, .list
	mov bx, .msg1
	mov cx, .msg2
	call os_list_dialog
	jc .esc_pressed

	; Now AX = number (from 1) of option chosen
	...

.esc_pressed:
	...

	.list	db 'Open,Close,Reboot', 0
	.msg1	db 'Choose an option', 0
	.msg2	db 'Or press Esc to quit', 0
</pre>


<br />


<h3>os_draw_background</h3>
<p><strong>Clear screen with white top and bottom bars, containing text, and a coloured middle section</strong></p>

<ul>
 <li>IN: AX/BX = top/bottom string locations, CX = colour</li>
 <li>OUT: Nothing</li>
</ul>

<p>Example:</p>

<pre>
	mov ax, .title_msg
	mov bx, .footer_msg
	mov cx, 00100000b	; Colour
	call os_draw_background

	...

	.title_msg	db 'File manager', 0
	.footer_msg	db 'Choose an option...', 0
</pre>


<br />


<h3>os_print_newline</h3>
<p><strong>Reset cursor to start of next line</strong></p>

<ul>
 <li>IN/OUT: Nothing (registers preserved)</li>
</ul>


<br />


<h3>os_dump_registers</h3>
<p><strong>Displays register contents in hex on the screen</strong></p>

<ul>
 <li>IN/OUT: AX/BX/CX/DX = registers to show</li>
</ul>