2.5 KiB
Varvara
Varvara is a personal computer, using the uxn instruction set, programmed in tal.
UXN presents 16 I/O ports via the DEI and DEO instructions.
Each port consists of 16 words of memory, and has its own I/O memory mapping behavior.
Note that while other memory read and write instructions can interface with port memory, only DEI and DEO will trigger port effects.
The Varvara computer presents the following canonical port mappings -
0x0000, System device0x0010, Console device (text output)0x0020, Screen device (bitmap output)0x0030, Audio device (audio0)0x0040, Audio device (audio1)0x0050, Audio device (audio2)0x0060, Audio device (audio3)0x0070, Unused0x0080, D-pad controller0x0090, Mouse0x00A0, File (file0)0x00B0, File (file1)0x00C0, Datetime0x00D0, Unused0x00E0, Unused0x00F0, ROM metadata on some implementations
Note that while ports have memory addresses, the 0 page is normal memory.
The DEI and DEO port I/O instructions have memory effects, but loads/stores to port mapped memory does not have I/O effects.
Varvara executes ROMS starting at 0x0100 until the BRK instruction occurs.
BRK does not halt the machine.
Instead it signals that the present 'thread' of execution has completed, and returns control so that an interrupt handler can occur.
Machine termination can be accomplished with %BYE { #01 #000F DEO BRK } which writes #01 to the System/state port, marking the machine as halted and breaks.
Varvara provides 'interrupt' based I/O.
The 'vector' of a given device is a program point.
That point will be invoked with no stack arguments when an event on the device occurs.
Threads of execution precede until they yield using the BRK instruction.
Typically the 'main' program starting at 0x0100 will initialize handler vectors and then BRK to enable I/O.
WARNING: BRK does not alter or reset either stack.
It is possible to perform (deliberate or accidental) communication between vectors due to this.
Devices
The system
The console
The screen
The screen device's vector is a clock which ticks at 60hz.
Audio
The controller
The controller device similarly fires on input changes.
The mouse
The mouse device's vector likewise fires when a mouse event such as movement or a button press occurs.