The video system is the most complex module of the machine following Sirius. Its main task is displayiing images and performing graphic oriented operations (COMING SOON). Its control registers are the following:
╭────────┬────┬────╮
│COMMAND │byte│ 0x0│
├────────┼────┼────┤
│DATAH │byte│ 0x1│
├────────┼────┼────┤
│DATAM │byte│ 0x2│
├────────┼────┼────┤
│DATAL │byte│ 0x3│
├────────┼────┼────┤
│GPU0 │byte│ 0x4│
├────────┼────┼────┤
│GPU1 │byte│ 0x5│
├────────┼────┼────┤
│GPU2 │byte│ 0x6│
├────────┼────┼────┤
│GPU3 │byte│ 0x7│
├────────┼────┼────┤
│GPU4 │byte│ 0x8│
├────────┼────┼────┤
│GPU5 │byte│ 0x9│
├────────┼────┼────┤
│GPU6 │byte│ 0xa│
├────────┼────┼────┤
│GPU7 │byte│ 0xb│
├────────┼────┼────┤
│STATUS0 │byte│ 0xc│
├────────┼────┼────┤
│STATUS1 │byte│ 0xd│
├────────┼────┼────┤
│STATUS2 │byte│ 0xe│
├────────┼────┼────┤
│STATUS3 │byte│ 0xf│
╰────────┴────┴────╯
The video system supports three basic modes:
Number 0, monochrome text mode of 80*25 characters. The characters are encoded as CP437 characters.
Number 1, a 16 color text mode of 160*50 characters. The characters are encoded as CP437 character code and a byte of attributes as follows.
╭────────┬──────────────┬──────────────╮
│blink: 1│ background: 3│ foreground: 4│
╰────────┴──────────────┴──────────────╯
This adds up to a total of 2 bytes per character. The colors are indexed into a configurable pallete (NOT BY NOW)
Number 2 , a graphic 256 color mode of 640*480 pixels. Pixels are represented a byte per pixel, encoding as rgb332 values.
A set of basic commands manage primary functions of the video controller, such as setting modes, fonts, and sending actual data to the screen. A command is issued by writing its number to it and setting the correspondent arguments in the data register.
0x0) Nop: do nothing.0x1) Clear: clear the framebuffer.0x2) Set Mode (dh: mode): sets the requested mode.0x4) Set Font (dh: font): sets the requested hardware font (if it does not exist, default to 0).0x6) Blit (dh-dm-dl): blits the framebuffer with the contents of the buffer at address dh-dm-dl.The screen refreshes 60 times a second (60hz), and issues a SCREEN_REFRESH interrupt to the cpu at priority level 6.