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Type-in arbitrary binary files on various operating systems

quorten

2019-08-08

Categories: unlipic  
Tags: unlipic  

How do you “assemble” a type-in program on modern Unix? How about some of the older but once popular operating systems?

  1. vi – type-in special characters and save. MS-DOS edit: the binary mode might be adequate.

  2. bash – write a shell script to convert hex type-in to binary.

  3. perl – same method as bash, but different language.

  4. python – same method as bash, but different language.

  5. web browser – similar to bash method, but using Javascript. Then download the binary file produced, via a data URI. May not work with some old browsers, unless server-side assistance is used.

  6. PowerShell – similar to bash method, but using PowerShell.

  7. bat files, NT cmd scripts – similar to bash method, but using bat or cmd files.

  8. vbs files – similar to bash method, but using Visual Basic Script (VBS).

  9. MS-DOS DEBUG – as its name suggests, for the sake of debugging, you get direct access to a hex byte code editor. You can type hex byte codes into memory and execute the produced program, or you can save to a file. You can even save to direct disk blocks.

  1. Mac OS Classic? Almost impossible, but there is a method.

    This method only works for “compact” Macintoshes, i.e. built-in black and white monitor and MC68000 CPU. Get a system boot disk, boot up, press the “programmer” key near the back side of the computer (need sticks to push through grills, see elsewhere on the Internet for more details), and enter the “MicroBug” ROM debugger. Note that this is not available on the Macintosh 128K, 512K, and XL computers, though.

    Late generation OS 9, impossible. AppleScript? Okay, maybe that’s the saving grace, if we have a way to write resource forks so that we can generate an executable application.

How about modern Windows? That’s a bit tougher. But, never fear, the web browser method is in business. Or, for sufficiently new Windows, PowerShell. For sufficiently old Windows that doesn’t have fancies, never fear, MS-DOS DEBUG is in business. For some Windows in between old and new, Visual Basic Script (VBS) is probably pre-installed and can fit the bill.

Once you have your binary file, you can execute it. In all cases, the first thing you’re going to want is the standard monitor program that gives you an easy low-level virtual monitor interface. A virtual computer without an MMU tantamounts to pretty much single-process execution. Yes, essentially it is similar a traditional 8-bit home computers.

Please, define that in the strictest, smallest, most limited sense. Okay, you have a terminal, command-line interface means to read and write memory as hex byte codes, and you can execute memory as machine code. That is the bare minimum.

The most immediate useful extension is to support checksum. List memory with checksum display. Simple XOR checksum is guaranteed to catch a single error, but two or more errors may be missed. Probability of misses is reduced by using longer checksum. A single swap error is guaranteed to be detected with at least a two-wide checksum.

Let’s discuss some metrics on our simple monitor program design.

Assume max 40 chars terminal width.
8 bytes a line, 3 * 8 = 24
4 chars address + 2 space = 6
8 chars checksum + 2 space = 10

8 chars checksum is overkill, 4 chars checksum is adequate

prob. checksum error on two errors = 1/16 * 1/8 = 1/128 = <1%

So keep a count of number of errors made so far. Worst case, can’t enter more than 128 lines reliably. Common case, maybe max 8192 lines reliably, or 64 KiB. And that’s why we only give the user a 16-bit address space.

Some immediately useful extensions are to support disassemble, single-step, and read/write registers. Assemble is more advanced, breakpoint is more advanced, and so on.

Tada! You’ve got a method to create arbitrary binary files on some of the most important modern operating systems in the style of type-in programs.

Natural next step would be to download the rest via serial port hardware, else you must type in A LOT of code. Plus, what’s the use of using a computer in the modern era without networking?

So to speak, my environment I am building out is like a modern version of Forth.

  1. Build the “front panel control switch.” On modern systems, this is a script to convert hex byte codes to binary.

  2. Key in the monitor program.

  3. Use the monitor program to key in larger programs.

  4. You’re in business!