This repository includes some bare metal programming experiments for 68040-based NeXT systems. While some open source operating systems for 68030/40-based NeXT hardware exist (e.g. NetBSD and Plan 9, there also was an early Linux port), documentation on low-level programming of the NeXT hardware is not widely available and information has to be extracted from existing OS sources or the code of the excellent Previous emulator. This little project is a small step towards providing more complete information and might help to create a NeXT hardware clone or a replacement Mach kernel in the future.
The code currently only supports a mono non-Turbo 68040-based NeXTstation in Previous. It is based on NetBSD's next68k port as well as the second edition Plan 9 NeXT sources. The Retro68 cross-compiler toolchain is used to build a 68k a.out boot file which is directly bootable via ben in the NeXT monitor using the emulated network in Previous 2.5.
Current functionality includes:
- Character output to the 2 bits/pixel bitmapped screen
- Interrupt handling for the timer interrupt (marked as vertical blank, auto interrupt 3 ISR bit 5), displaying a seconds counter
- Interrupt handling for keyboard and mouse (auto interrupt 3 ISR bit 22)
- Keyboard code to ASCII translation (lowercase only at the moment)
- Mouse pointer drawn using XOR
Network booting is possible since the NeXT firmware still supports the old a.out executable format in addition to Mach-O. The method to generate an a.out-file from the gcc/ld-generated ELF binary was copied from NetBSD's NeXT bootloader and is a big horrible hack...