Varvara
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Varvara is a fantasy computer system that uses runs a stack-based virtual machine called Uxn. Its main programming language is a Forth-like language called Uxntal.
Uxn
Memory
The Uxn virtual CPU can address 64kb of memory; programs can move stacks into addressable range to allow reading and writing directly into stack memory. In this way, peripherals such as a controller, mouse, and keyboard can be addressed.
| Memory | RAM | Data | 64kb |
|---|---|---|---|
| Stacks | Working Stack | Data | 254 bytes |
| Error | 1 byte | ||
| Pointer | 1 byte | ||
| Return Stack | Data | 254 bytes | |
| Error | 1 byte | ||
| Pointer | 1 byte | ||
| I/O | Devices | Data | 256 bytes |
Uxn is a single-page virtual machine with 32 opcodes. This system has no registers, and instead uses a 127-level stack.
Devices
Devices are external systems connected to the Uxn CPU, such as the screen, the mouse and the keyboard. Each device has 16 bytes, also called ports, of I/O memory. Vectors are ports holding an address in memory to evaluate when a device event is triggered, such as when the mouse is moved, or a key is pressed.
- 00 - System device
- 10 - Console device
- 20 - Screen device
- 30, 40, 50, 60 - Audio device
- 70 - MIDI device
- 80 - Controller
- 90 - Mouse
- a0, b0 - File
- c0 - Datetime
- d0 - Unused
- e0, f0 - Reserved
The two reserved devices can be used for implementation specific features that do not need to be part of the specs, or other Uxn/Varvara instances.