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nanochess / tinyasm

Tiny assembler for 8086/8088, able to run over DOS for 8086/8088 machines.

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Tinyasm 8086/8088 assembler by Oscar Toledo G. Oct/02/2019

https://nanochess.org/ https://github.com/nanochess/tinyasm

Tinyasm is a small assembler for 8086/8088 programs, and it can work over a real PC XT machine. It requires at least 128K of memory, maybe more.

It came to my attention that several people wanted to assemble my boot sector games over real PC XT machines.

Unfortunately, nasm doesn't run over 8086/8088 processors, and I couldn't find a compatible assembler!

So what does a programmer when doesn't find the required tool? Start to code his own tool!

It took me 3 days to start from zero and get a working assembler compatible with the nasm syntax, plus all the directives I've used in my boot sector programs.

Using the same command line syntax as nasm:

tinyasm -f bin rogue.asm -o rogue.img -l rogue.lst

There is also the -d option for defining labels:


It returns a non-zero error code when the assembled file generates errors.

Thanks to tkchia for making it portable to ia16-elf-gcc, removing DeSmet C warnings, and making it to return error codes.

Thanks to humbertocsjr for contributing the INCBIN command.


The main difference is that Tinyasm won't insert long jumps for miscalculated conditional jumps.

Labels are started with letter, underscore or period. Case is insensitive.

Local labels are supported, and should start with period. The local labels final name is derived from concatenation of the last global label (not starting with period) and the local label.

There is only support for 8086/8088 processors, and only are implemented the following directives:

cpu 8086

The following operators are implemented:

|   Binary OR
^   Binary XOR
&   Binary AND
<<  Shift to left
>>  Shift to right
+   Addition 
-   Subtraction 
*   Multiplication 
/   Division (unsigned 16-bit)
%   Modulo operator
(expr)  Parenthesis
-   Unary negation

The following numbers are implemented:

0b0000_0100 Binary, you can use underscore (it will be ignored)
0xabcd      Hexadecimal.
$0abcd      Hexadecimal (after $ the first digit must be a number)
'a'     Character constant.
10      Decimal.
$$      Start address.
$       Current address.

This assembler won't win a speed test ;) because the internal implementation uses a linear search for the instruction set, and it is also implemented as a kind of regular expression subset for easier coding.


If you're building boot sector games with Tinyasm, then you need the following info to load the game inside the boot sector of a floppy disk.

You need to have DEBUG in your disk (included with the DOS disks).

Do the following (replace filename as desired):

    Extract now your working disk and insert a blank one!!!
MOV AX,0301
MOV BX,0100
INT 13
JB 300
INT 20
    Now the boot sector is replaced with the program!!!


You can build your own executable for Tinyasm using the C compiler Desmet C, version 3.1h available graciously at:


The compiler has many bugs and limitations, but it works for tinyasm purposes, and it's freely available.

Supposedly it should support ANSI C, but I couldn't fit a standard ANSI C function definition, so I had to code again in C K&R for the first time in maybe 20 years!

You can find the "e.bat" file to assemble the compiler.

I provide an executable on the Git to save you some time.

There are test cases in the 'test' subdirectory that are runnable with the "test.bat" file.

There is a test for the full instruction set of 8086/8088 (the same listing that appears in my book Programming Boot Sector Games).

The test cases come from my own programs:



Would you like to learn 8086/8088 programming? Then you must get my new book Programming Boot Sector Games including a 8086/8088 crash course!

Now available from Lulu:

Soft-cover http://www.lulu.com/shop/oscar-toledo-gutierrez/programming-boot-sector-games/paperback/product-24188564.html

Hard-cover http://www.lulu.com/shop/oscar-toledo-gutierrez/programming-boot-sector-games/hardcover/product-24188530.html

eBook https://nanochess.org/store.html

These are some of the example programs documented profusely in the book:

  • Guess the number.
  • Tic-Tac-Toe game.
  • Text graphics.
  • Mandelbrot set.
  • F-Bird game.
  • Invaders game.
  • Pillman game.
  • Toledo Atomchess.
  • bootBASIC language.

After the success of my first book, if you need even More Boot Sector Games then you must get this book!

Soft-cover http://www.lulu.com/shop/oscar-toledo-gutierrez/more-boot-sector-games/paperback/product-24462035.html

Hard-cover http://www.lulu.com/shop/oscar-toledo-gutierrez/more-boot-sector-games/hardcover/product-24462029.html

These are some of the example programs documented profusely in the book:

  • Follow the Lights
  • bootRogue
  • bricks
  • cubicDoom
  • bootOS

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