GEM is truly truly outrageous
@Seg@oldbytes.space  ·  activity timestamp 3 weeks ago

using the incredible compatibility afforded by the front panel headphone jack, i can write a tape from a modern PC and load it into the ZX81

and i run headfirst in to z88dk's limitations, compiling with sccz80 renders in a lethargic 5.4 minutes, sdcc is much faster at 2.5 minutes

but sdcc doesn't seem to support the ZX81 compatible floating point library, so it glitches the video

the inner loop is 16bit fixed point but using it all the way through gets real raunchy precision wise so i thought i'd just use floating point on the outside hahahah

https://www.youtube.com/watch?v=XxWg5hIT2fo

#retrocomputing
#sinclair#ZX81
GEM is truly truly outrageous
@Seg@oldbytes.space  ·  activity timestamp 3 weeks ago

anyway here's a patched z88dk that cleans up the ZX81 tape output, whoever wrote it clearly wasn't a DSP signals person 😬

https://github.com/SegHaxx/z88dk

makes it all nice and symmetrical, no more DC offset

i'll make it nice sine waves someday

...i was unable to write readable tapes and after driving the SO nuts listening to screeching i determined the super clean outputs on a modern PC cause the vintage cassette recorders aggressive AGC to max out, resulting in mangling the signal when it comes in

the ZX81 has zero error correction and this fails the load

after adding a pilot tone inspired by the Apple II i can write tapes that load 100% reliably and it gives you something to orient on when scrubbing through a tape looking for the start of a file

it also shows as a solid white screen on the ZX81

near as i can tell a real ZX81 is so goddamn RF noisy the video buzz fulfills the same purpose of priming the recorder's AGC

80's tech, man ¯_(ツ)_/¯

...with that i'm kinda burned out on the ZX81 lol

#retrocomputing
#sinclair#ZX81