Mega65 Compatible FPGA board

[Jimbo7136]

In the Mega65 manual, there's a section for building a Mega65 compatible computer from an fpga board: https://digilent.com/shop/nexys-a7-fpga-trainer-board-recommended-for-ece-curriculum/.

Would it be possible to use cores ported to Mega65 on such a board?

Thanks in advance.

[MJoergen]

Short answer: It requires some additional work.

Explanation: The FPGA in the MEGA65 is identical to (or at least very similar to) the FPGA on the Nexys A7 board. However, the I/O ports on the MEGA65 and the Nexys A7 boards are different, and the physical pin connections of the two FPGAs are different too. So it requires some work porting this project to the Nexys A7 board. However, this work only needs to be done once.

The work required involves writing a new top-level file (based on MEGA65/vhdl/top_mega65-r3.vhd or perhaps MEGA65/vhdl/top_mega65-r2.vhd) and a new constraint file replacing MEGA65/MEGA65-R3.xdc. Getting VGA output should be fairly easy (just assigning new pin names in the constraint file). But all other interfaces are different, i.e. the keyboard interface is completely different and the HDMI output is handled differently too.

That being said, the total amount of work is not too hard, and much of it has already been done by the MEGA65 team and inspiration can be found in the MEGA65/mega65-core repository, i.e. src/vhdl/nexys4ddr.vhdl and src/vhdl/nexys4ddr.xdc.

If you like, you may create an issue asking for the added feature of porting the framework to the Nexys A7 board. And you're even welcome to do this porting yourself and submit a Pull Request 😄