raspberry pi 4B: writing to screen buffer / framebuffer

Question

In the old days you could bypass system calls, bios calls, etc. by writing an ASCII character directly to a byte in the "screen buffer". Is there something similar with the raspberry pi 4b?

• user115418: Something like github.com/JSBattista/Characters_To_Linux_Buffer_THE_HARD_WAY Not sure why you would want to do it :-)
• sashley: @Andyroo , thanks for the helpful link. If I have to, I'll delve into JSBattista's deep exploration of the framebuffer, but I'd like to avoid it. On my first computer, an Osborne One, it was a simple matter to display any ASCII character at any desired location on the screen by writing it to the right byte in the screen buffer. I was hoping that something similar would work on my new raspberry pi 4.

Answer 1

Strictly speaking, no. The video output of the Pi is under control of the VideoCore, not the ARM CPU.

You can allocate a framebuffer and use low-level memory writes to fill it, but you'll still have to talk to the the VideoCore to get it displayed.

In a less strict sense, you could consider the VideoCore as an equivalent of the VGA adapter hardware. It's a question of what you would be willing to call "direct access".

• sashley: Messing about with the VideoCore is way more complicated than what I had in mind. The best solution I have come up with is the ncurses package, which implements the kind of functionality that I described. When you compile and link a program, you have to tell GCC (or whatever compiler you're using) to link in the ncurses library.