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STM32F401 Apple-1 Replica Emulator

Question asked by de_simone.francesco on Sep 22, 2016
Latest reply on Sep 22, 2016 by de_simone.francesco
Hello to All, 

recently I coded an emulator of an old Apple-1 inside a STM32F401 Discovery board. It is capable to generate a PAL/NTSC composite video signal, it's interfaced to an old Macintosh 128K keyboard through an Arduino Mini Pro. Currently all programs made for the Apple-1 can run on it, but now I am trying to develop a driver/interface to save or load program to/from a tape player. This is a tricky part because it should run almost in real time to save the signal correctly. 

I am evaluating different options, but it's not easy because the clock of the emulated 6502 has to be 1Mhz, and I can't use an interrupt to execute one instruction a time without interfere with the TV signal generation. 

The 401 is clocked at 84MHz, I was wondering if using something faster like a 429 the 1MHz interrupt can be handled better.