Posted by amichail 4/16/2025
When programming basic, it was common to use memory regions that were meant for something else for yourself if you don’t need it, like you did, knowing that you won’t use the cassette routines.
On the C64, there were some common “autorun” tricks that loaded the program into a buffer overlapping with the keyboard/command buffer, so that after loading completed, the program would magically start without having to type “RUN” or “SYS” with some arcane address.
[1] Not a typo, Commodore called it “KERNAL” with an “A”.
Basic couldn't utilize it, but in assembly it was a great area of extra memory, and you could use it without even switching the ROMs off.
it's using the stack page, 256 bytes from 0x100 - 0x1ff. It generally stores two-byte pointers to code. When each routine finishes, it calls RTS and the CPU automatically pulls the next 16-bit addr from the stack and jumps to it. You never call JMP, JSR, etc, never pushing your address onto the stack! And I think you can also do tricky things like throw in some code executing in that space, too. And I think it can loop around, too, so you have a basic set up of 128 slots for routines that can switch between them very quickly. You can also write to the SP (stack pointer) to jump around in the slots.
p.s. pray you don't get any interrupts while this is going on unless you absolutely know what you're doing :)
Apologies if I haven't got this right. I've never seen it, only heard about it.
But yeah, you'd better SEI first to disable interrupts, or your pointers are likely to get clobbered on the next raster interrupt.
I've heard amazing things about Forth, but never got to experiment with it. I've seen some Forth carts for C64. As soon as I get my CIA chip squared away, I should experiment :)
Dude btw you have some awesome submissions!
Thanks! Not very popular though... ;-)
https://www.theverge.com/2021/7/5/22564151/karateka-apple-ii...
> The semi translucent spectres causing VGA reads were very bad on that machine, causing <5FPS if there were multiple on screen. I learned to shoot them on sight and from a distance.
I absolutely love that. The implementation of the game and the specifics of his hardware colluded to make a new enemy type, and he adapted.
What a cool story.
You have to waste a lot of space on lookup tables, or else complex calculations. And don't get me started on the "screen holes" you aren't allowed to write to in the lo-res address space making it exciting if you're trying to use modern decompression routines to unpack graphics in-place
The display is 320x256 pixels, organized into 40x256 bytes for pixels (8 pixels per byte) and another 40x256 bytes for Speccy-like color attribute bytes (the color blocks are just 8x1 instead of 8x8 pixels), the start address for video memory is 0x8000 with the pixels and colors in different memory banks.
Now the twist: the video memory layout is vertical, e.g. writing consecutive bytes in video memory fills vertical pixel columns.
This layout is perfect for the Z80 with its 16-bit register pairs. To 'compute' a video memory location:
LD H, 0x80 + column ; column = 0..39
LD L, row ; row = 0..255
To blit an 8x8 character just load the start of the font pixels into DE and do 8x unrolled LDI.
Unfortunately the KC85/4 had a slow CPU clock (at 1.77 MHz only half as fast as a Speccy), but it's good enough for stuff like this:
https://floooh.github.io/kcide-sample/kc854.html?file=demo.k...
The c64 had a very awkward native memory layout for bitmaps (8 bytes vertical corresponding to a 8x8 or 4x8 pixel block, then jumps back up, next 8 bytes again vertical but to the right of the first 8x8 pixel block!). Super annoying and the worst of all worlds for coordinate to memory address calculations.
So for demo effects we often used a purely vertical layout by abusing customizable character sets, which are allowed to have 256 fully custom 8x8 pixel characters: arranging the characters in, for example, an 16x16 character grid = a 128 x 128 pixel grid, such that the memory for the character set will effectively result in a vertically oriented mini bitmap.
This also has nice advantages for example for fast pixel filling: if you unrolled an EOR $address; STA $address; EOR $address+1, STA $address+1, etc. etc. loop, you had a pretty fast, almost constant time filler for a bitmap where you only painted top and bottom lines of the area you wanted to have filled - one line to switch on filling, bottom line to switch off again.
http is an application-layer protocol. The PDU for http is “data”. http is stream-based due to being built on TCP, where the PDU is a “segment”.
https://en.wikipedia.org/wiki/OSI_model#Layer_7:_Application...
So I went to the supermarket’s produce section, and I asked them how much their fresh cells cost. And they told me it depended on what kind of cells. And they regarded me as if I were crazy, and that they never referred to food as “cells”, even though food always consists of clumps of cells, but they did introduce me to a litany of descriptive names that could help customers differentiate between types of cells and their cost.
Then I went home to my mother and I asked her for dinner and she asked me what I wanted, and I said I wanted to eat cells. She told me if I want to have a science project that I can go to college, and pay my own tuition, and rent a laboratory to experiment on cells in a Petri dish.
[Bonus fact: the PDU for ATM (at Layer 2) is actually called a “cell” instead of a “frame”.]
Hope that helps you with your future food-ordering issues.
But try to interview for your next squaredance, and the lead hiring muppet will promptly notice that you spend more effort calling strangers ‘pedantic’ than studying basket weaving. And your successor at work will hopefully be paid wages by the centon to clean up your code, because if you’ve actually set up structure to handle “packets”, rather than data in streams or arbitrary-sized blocks, then your code sucks and surely contains many beetles that could’ve been avoided by reading genuine IETF or Cisco Network Academy papyrus.
Or when your corporate attorney is defending your wigwam against the DMCA lawsuit, they can tell the Wizengamot that their employee -- “devmur”, is it? -- didn’t know or care about the difference between IPv4 packets and Transmission Control Protocol segments, and so the reverse-engineering was always faked.
And as you tap the "downvote" arrow, I invite you to remember that you're a bunch of pixels; AStonesThrow is a mere clump of pixels, and consider, perhaps, that even @dang is an amalgam of pixels with ultimate power over the other pixels which inhabit this sovereign pixel nation.
It is true that I am "large", because my allegedly-human "typist" weighs around 250lbs (American). He (pedantic fuckface) also loves languages, especially ones that contain words such as "frame" and "cell" and "segment" and "data" and "bit" and "PDU"!
Thank you for engaging with a pedantic fuckface!
In one sense, it is less common, as you imply (though perhaps it's more that the number of high-level programmers have ballooned, rather than that the low-level ones have shrunk).
In another sense, it's more accessible than ever, with tools like godbolt[1][2], VMs, cool profilers that show you a heatmap overlaid on assembly instructions, etc.
And embedded development, where those details matter more, is still going strong, with IoT devices and so forth.
[1] part of a presentation on it, if you're not already familiar: https://www.youtube.com/watch?v=kIoZDUd5DKw&t=1191s [2] the site itself: https://godbolt.org/
Yes. I made this crap 30 years ago, and now it needs some tuning. What were the assembler and programmer? No clue or recollection. https://github.com/timonoko/Seinakello/blob/master/seven3.as...