Work in progress.
- Z180 CPU,
- 1 MB of static RAM,
- 16 KB bootloader ROM,
- Floppy disk drive,
- 16 bit GPIO user port,
- 2 UARTs: USB-C and RS232,
- AY-3-8912 sound,
- 80x60 B&W text mode VGA output,
- custom Cherry-MX mechanical keyboard,
- USB-C powered.
ROM bootloader functions solely to load the kernel image from the 1.44 MB 3.5"
FDD that is stored in /BOOT/KERNEL.IMG file on FAT12 file system.
The kernel is a multi-tasking, preeptive, of monolithic architecture, with
UN*X-like features (not even close to the full POSIX compability). Hopefully,
it will be possible to port some UN*X applications (like vi), although limited
user process address space may present an obstacle (56 KB + 4 KB of stack).
The boot process is somewhat complicated due to the limited nature of the Z180 MMU.
First the bootloader copies itself to the high RAM, configures the MMU to divide
the address space into 3 regions and continues execution from the Common 1 area.
This enables the bootloader to disable ROM and allow the computer to access the
low RAM, that was previously occupied by ROM - this is the place kernel will be
loaded into. The kernel image is then loaded from the floppy disk from a file
/BOOT/KERNEL.IMG that resides on a FAT12 filesystem. After that the kernel is
executed.
The kernel reconfigures the MMU again to create a separate stack area and a "window" to access arbitrary physical memory. After initialization of all kernel subsystems, the first application is executed - init process, located at `/BOOT/INIT.ZEX'.
Init process executes a simple script located at /BOOT/INIT.INI that setups
the console (stdin, stdout, stderr) and executes next processes - for now only
a shell zesh.
| Start | End | Description |
|---|---|---|
| 0x00000 | 0x03FFF | ROM, disabled after boot, after that RAM |
| 0x04000 | 0xFDFFF | RAM |
| 0xFE000 | 0xFFFFF | Memory mapped I/O, VGA VRAM |
8-bit I/O is used.
| Start | End | Description |
|---|---|---|
| 0x00 | 0x3F | Z180 internal I/O |
| 0x40 | 0x5F | VBLANK IRQ acknowledge |
| 0x60 | 0x7F | ROM disable control |
| 0x80 | 0x9F | Keyboard |
| 0xA0 | 0xBF | Z80 PIO (user port) |
| 0xC0 | 0xDF | AY-3-8912 |
| 0xE0 | 0xFF | 82077 floppy controller |
| Region | Logical start | Logical end | Physical start | Physical end | Description |
|---|---|---|---|---|---|
| Common 0 | 0x0000 | 0x5FFF | 0x00000 | 0x05FFF | Kernel entry point |
| Bank | 0x6000 | 0x7FFF | N/A | N/A | Memory access |
| Common 1 | 0x8000 | 0xFFFF | 0xE8000 | 0xEFFFF | Code and data |
| Region | Logical start | Logical end | Physical start | Physical end | Description |
|---|---|---|---|---|---|
| Common 0 | 0x0000 | 0xDFFF | 0x00000 | 0x0DFFF | Kernel code/data |
| Bank | 0xE000 | 0xEFFF | N/A | N/A | Memory access |
| Common 1 | 0xF000 | 0xFFFF | N/A | N/A | Switchable stack |
| Region | Logical start | Logical end | Physical start | Physical end | Description |
|---|---|---|---|---|---|
| Common 0 | 0x0000 | 0x0FFF | 0x00000 | 0x00FFF | Kernel entry |
| Bank | 0x1000 | 0xEFFF | N/A | N/A | User code/data |
| Common 1 | 0xF000 | 0xFFFF | N/A | N/A | Switchable stack |
Collection of useful datasheets, might be removed in the future.
Source code of a bootloader ROM that is located on the internal EPROM memory.
ZAK180 peripheral drivers, both internal of Z180 MPU and present on the SBC. This includes:
- Z180 ASCI,
- Z180 MMU,
- AY-3-8912,
- 82077,
- Z80 PIO,
- VGA.
Legacy FAT12 implementation that is used by the bootloader. To be replaced with the implementation used by the kernel.
Source code of the kernel of the computer operating system.
Root filesystem skeleton. Populated with static files (e.g. INIT.INI) and
files created during firmware compilation. Later used to prepare a floopy disk.
Simple dead or alive SBC test. All it does is writing to the ASCI1 (USB-C) at 19200 bn1.
User space programs. This includes init process, zesh shell, utilities and
miscellaneous applications.
Script to build all components of the firmware.
Builds the firmware (by invoking build.sh) and copies the root file system
structure to the floopy disk.
Subrepository that contains a hardware project of a mechanical keyboard for the computer.
KiCAD project of the computer's PCB.
HDL of the VGA timing generator implemented in a XC9535 CPLD, tool to generate font ROM.
Schematic of the computer in a friendly .pdf form.
3D models designed for FDM priting.