This week, aside from helping with the presentation and discussing the overall plan with Joseph, I worked on research for the Audio, Input, Software, and Communication systems. I’ve attached a copy of my notes.
Suffice it to say, the current plan for audio is to have a single channel of 8-bit PCM audio and 32KHz, which will be representative of the GBA in sound power. Note that our users will be able to produce better sound, as they aren’t bound to a 16MB cartridge, though. Audio will be output by sending samples supplied by the CPU over I2S to the HDMI output. The interface itself hasn’t been designed yet, as I’m not sold on how it should be done specifically, so I’m a touch behind. I plan to get that done as soon as possible, and I’m confident I can be back on track by the end of next week.
For input, we plan to use a SNES controller over GPIO. I go over the details of the SNES controller communication protocol in my notes. It’s a simple protocol thats clocked well below what our FPGA will be clocked at. It should be relatively simple to bring up, as long as we can find controller ports.
For software, I took another look at the C standard and realized that our requirement of providing it to the user is completely infeasible if we are also creating our own kernel. The C standard has a lot to say about what an OS should provide, and we won’t be providing much of it. I’ve narrowed it down to a useful subset, which is listed in my notes.
For communication, I spent way too much time trying to understand how the FPGA and HPS communicate with each other. From what I can gather, the last GB of the HPS’ address space is mapped to the HPS-to-FPGA AXI bridge, and reading from/writing to it will send a signal to the FPGA that it can interpret and respond to. I think I’ll have to run some experiments when I get my board to convince myself of this. I’ll also need to spend some more time with the Cyclone V manual, it seems.
Finally, I also wrote a small C program to convert 16-bit 32KHz Mono Microsoft PCM Wave audio to pure 8-bit samples. It works with all the wave files I’ve exported from audacity into this format, though I didn’t rigorously test it. I did this so that once the audio system is brought up, we have working audio to make a direct comparison against. The program will also output 8-bit wave form audio in the wave format, so that it can be played on a computer and compared to our FPGA’s output. The source code for the program has been attached as well, though I’ve not tried building it on Windows/Mac.