First (Simulated) light

I have spent the last two days running PortaCore through Altera ModelSim. This is an application that lets you simulate the behaviour of your digital logic designs and see the resulting waveforms. Not only those coming out of your proposed chip, but those buried deep inside the logic modules (e.g. the ULA clone).

Tonight, the simulation has successfully:

• Read bitmap and attribute data from contended RAM
• Executed code from the overlay ROM
• Triggered the un-overlay trap at 0x1FF0 - 0x1FFF
• Program counter jumped back to 0
• Executed code from the original 48K ROM

I am now confident that the FPGA will run well enough to see something useful happening, so tomorrow the ordering of parts begins.

This is what an entire ZX Spectrum looks like when simulated:

Not bad for two weeks work.