Gigatron Hackers

It turns out that binary constants are not in the C standard!
Yet GCC implements them and C++ requires them.
That's easy to add.

It seems that there is a promising path using the Adafruit floppy interface https://www.adafruit.com/product/5679 and a Raspberry Pico because they also provide a nice controller library https://github.com/adafruit/Adafruit_Floppy/ with read support (write support seems to be under development). One...

If I had the time, I would use the RP2040 version and program it to act as a SPI device obeying a subset of the SD card protocol. Then the SPI browser would work out of the box. As for writing to the floppy, I always meant to add an OS layer and writing support to the SPI SD interface. The idea is t...

Why no DEC instruction? Having a DEC(b) instruction that runs as fast as INC(b) would take four precious bytes in page 3. Having a DECV(v) that runs as fast as INCV(v) would take two precious bytes in page 3. I have only four free bytes left in page 3 which I believe are best kept to organize a new ...

You can use program gt1dump (in the Utils directory) to look at GT1 files.

Also: only the first segment can have hiAddress=0. Otherwise it means that the GT1 file is ending with an exec address.

See function. GMem::load() in https://github.com/lb3361/gigatron-rom/ ... z/gt1z.cpp

Phibrizzo wrote: ↑23 Jan 2024, 18:44 I was based on https://github.com/lb3361/gigatron-rom/ ... ummary.txt

LUP is an instruction whose meaning has been hideously perverted by the return-from-interrupt mechanism

Hello :) I have a few questions. 1. In documentation, RTI (Return from interrupt) is a sequence of asm codes. Latest is LUP. What is the parameter for LUP? Any? 2, In the same documentations wrote, a LUP changes vAC. Then for what vAC is saved if interrupt came? Are you speaking of the file in dire...

  Virtual interrupts Virtual interrupts (vIRQ), introduced in ROMv5a. Variable "frameCount" (0x0e) is incremented sixty times per second, at the beginning of each vertical blank interval. When it reaches zero, the Gigatron checks the contents of "vIRQ" (0x1f6-0x1f7). If this is a...

With 8 pixels per byte, each row is encoded on three bytes, meaning 73 * 3 = 219 bytes. There is a free bit in each row. So each row could be composed of a first byte in range 0-127 (7 pixels) and two bytes in range 0-255 (8 pixels each). One could code special situations by having a first byte in r...

The cheapest way to clear the screen is: _console_clear((char*)0x800, 0x00,120); /* 0x00 is the background color */ This calls SYS_SetMemory 120 times, one for each row of the screen. No dependencies. You can add option --no-runtime-bss to save another 100 bytes or so. Instead of "SYS_Random() ...