So I have a project designed around the PCduino 3B board, just the updated PCduino. My project is to run android through the board across a lcd tft nextion 4.3" screen. PCduino has ubuntu and android automatically loaded to the board but this OS is intended to be hooked up to a common keyboard, mouse, and monitor via the HDMI and USB. The nextion screen needs only the pcduinos UART2 RX, UART2 TX, 5v DC, and GND pins to boot. So how do I program the android image to connect to the screen via these pins? Ideas? PCduino 3B link: https://www.sparkfun.com/products/13707
If you want it to display the normal Android UI on that screen, you find or write the appropriate android display driver. If you cannot find them, writing it will be very challenging. Performance will suck (because you can't send data very quickly over serial. Think seconds per frame, not frames per second.
If you want to draw to it directly (ie, have a program on there that drew what it wanted) that would be easy - just write a program to send the appropriate data to it (see the datasheet and/or documentation that came with the screen).
Those sorts of UART interface displays are usually have a microcontroller driving the screen directly via SPI or that parallel interface a lot of microcontrollers use for displays, and are designed for applications where your microcontroller doesn't have the resources (speed, ram, pins in the case of parallel) to drive the screen directly, and often implement a bunch of operations in the firmware of that microcontroller, so your little microcontroller doesn't have to waste flash on graphics stuff. They're not really the right tool for the job when you have a near-PC-spec microprocessor and GPU. If you're going to control a non-HDMI screen, you should start by looking into whether you can get a driver for any SPI displays - and then see if you can score the matching display. SPI can be much faster than UART, and you're more likely to find drivers for a standard SPI display (ie, like the one that the controller in your UART display is driving!)