Impressive. At least for me :-0 Regards Sergio
2017-04-05 16:43 GMT+02:00 Kyle Owen via cctalk <cctalk@classiccmp.org>: > I suspected that I could somehow get some music out of the SimH PDP-8 > simulator for a while now, if I could only make it run real time and toggle > a GPIO pin fast enough say, on a Raspberry Pi. That may still be doable in > the future, but I also had a suspicion that I could generate music not in > real time. > > I finally got around to trying out my idea last night. A few lines were > added to pdp8_cpu.c to spit out the elapsed instruction cycles every time a > CAF instruction is executed, the default "noise" instruction in the MUSIC.PA > program. > > That's all I did to the simulator. I then ran MUSIC with a given .MU file > and watched as many integers are spit out onto the screen. These were > copied and pasted into a new text file and saved. > > The rest of it is in a single C program that I cobbled together. It reads > in this new text file and generates a series of pulses as an array of > floats. Each interval is about 1.93 microseconds, which I calculated to be > the average number of pulses for the music program to be "in tune" with > A=440 Hz, plus or minus. This value is subject to change, particularly as > the notes get higher in frequency, but only by perhaps 6% or so from my > experiments. One detail to note is that per the recommendation of the > MUSIC.PA manual, these pulses are extended to roughly 6 microseconds, or > three time intervals in my program. > > This array of floats is then downsampled use libsamplerate to 44.1 kHz > (from 1/1.93 microseconds, or roughly 520 kHz) and output to a canonical > WAV file, 16-bit single channel. > > What do you know, it worked! Here's a sample: > https://www.youtube.com/watch?v=_urDcyluX9c > > My code can be found here, for those interested: > https://github.com/drovak/music > > Presumably, this technique could be used to generate music from any given > computer simulator. > > Thanks, > > Kyle