To enable more verbose debug logging at runtime, I have added a higher-resolution LCD. Communication from the 65816 is handled with SPI. So far, performance of the display seems quite good.
The LCD is a 3.5" TFT with 480x320 resolution. I selected a screen without touchscreen support. These LCDs are available on Amazon for less than $20 USD. The LCD connects to an Arduino Mega 2560 as a shield. I am leveraging Bodmer's TFT library on the Arduino.
This video (from adventurelaus) shows the 3.2" version of the screen running a demo loop. The video also has additional details on setting up the screen. I am not using the library mentioned in this video (see Bodmer library link above).
For SPI communication, I am bit banging it from VIA1 in my system. I found that bit banging with my 14 MHz 65816 was too fast. I had to add delays after all SPI-related writes (i.e., CS, MOSI, SCLK). I'll setup some rapid logging of data in the coming days and see how the LCD performs. So far, I have no concerns about performance. I could possibly even animate Mario on the display; maybe, if I get really bored, I'll do that. :) The 65816 is the SPI master, with the Arduino Mega 2560 being the slave. I have implemented a simple command+data setup for SPI communication. This configuration will allow me to handle many different types of calls from the system to the Arduino.
I'll post an updated video once I get some better visuals on the LCD.
After a little wiring clean-up...