4 ms·

I don't know much about the Apple II but I'm surprised that external circuitry is required to effectively count the number of frames. Isn't there already a way

by simias 7y ago

I don't know much about the Apple II but I'm surprised that external circuitry is required to effectively count the number of frames. Isn't there already a way to count the number of frames without hardware hack on this computer? Beyond that, an RTC without battery backup to maintain the time across reboots might not be extremely useful. Given the low precision I'd consider this more like a hardware timer than an RTC, but I'm probably splitting hairs now. It's still a cool hack nonetheless, it's always refreshing to see how simple and straightforward it is to hack these old machines, both in hardware and software. Can you imagine doing something like that on a modern system? I mean, it's doable but it'll take more than three lines of assembly to get it to work correctly.

sehugg 7y ago
Nope. You can't even write a busy loop that syncs with the frame rate because the ][ lacks a VSYNC flag. Some modern demos manage to read the beam position, though -- they look at values on the bus left over by the video circuitry when the bus is floating (the "vapor lock" hack)
- djmips 7y ago
  The technique is from 1982 by Bob Bishop. http://rich12345.tripod.com/aiivideo/softalk.html http://rich12345.tripod.com/aiivideo/softalk.html
  - sehugg 7y ago
    Ah, thanks -- I must have missed that issue! :)
pjc50 7y ago
It's an 8 bit system; you need explicit hardware to do everything. The nearest things I can think of in terms of modern hacks would be tapping into the SMbus on the motherboard, or the I2C bus exposed on the VGA connector, e.g. https://dave.cheney.net/tag/i2c https://dave.cheney.net/tag/i2c
- segfaultbuserr 7y ago
  Good post. I was working on a video card driver for the Linux kernel and I was often wondering if I can configure the i2c pins on the VGA connector as a generic i2c device and connect my sensors to it. So the conclusion is clear now, a lot of people have tried it with success. The possibilities are endless, you can even connect a I/O extender... This is impressing, even when the serial and parallel ports have all retired, most computer still has a "User Port" like a 8-bit computer ;-)

by simias 7y ago

sehugg 7y ago

Nope. You can't even write a busy loop that syncs with the frame rate because the ][ lacks a VSYNC flag. Some modern demos manage to read the beam position, though -- they look at values on the bus left over by the video circuitry when the bus is floating (the "vapor lock" hack)

djmips 7y ago
The technique is from 1982 by Bob Bishop. http://rich12345.tripod.com/aiivideo/softalk.html http://rich12345.tripod.com/aiivideo/softalk.html
- sehugg 7y ago
  Ah, thanks -- I must have missed that issue! :)

pjc50 7y ago

It's an 8 bit system; you need explicit hardware to do everything. The nearest things I can think of in terms of modern hacks would be tapping into the SMbus on the motherboard, or the I2C bus exposed on the VGA connector, e.g. https://dave.cheney.net/tag/i2c https://dave.cheney.net/tag/i2c

segfaultbuserr 7y ago
Good post. I was working on a video card driver for the Linux kernel and I was often wondering if I can configure the i2c pins on the VGA connector as a generic i2c device and connect my sensors to it. So the conclusion is clear now, a lot of people have tried it with success. The possibilities are endless, you can even connect a I/O extender... This is impressing, even when the serial and parallel ports have all retired, most computer still has a "User Port" like a 8-bit computer ;-)