Commander X16

TomXP411 wrote: ↑Thu Oct 26, 2023 5:09 amThere has been a lot of talk over the years about using VERA; it's pretty well documented and thoroughly discussed.

TomXP411 wrote: ↑Thu Oct 26, 2023 5:09 amHere's the VERA manual
https://github.com/X16Community/x16-doc ... ference.md

TomXP411 wrote: ↑Thu Oct 26, 2023 5:09 amShort version is that VERA uses vectors to write to video memory. You set the 3-byte address by setting 3 port values. (Part of the address is the increment value, which you use if you are writing horizontal or vertical lines.)
Then you write to the data port. Whatever you write to the data port gets written to video memory. If you have set an offset, then you can just keep writing data values to the data port, and the address in the address register will increment based on the set value.

Address $9F20 is the low 8 bits of the Video memory address.
$9F21 is the upper 8 bits
$9F22 is the address increment (upper 4 bits), DECR flag (bit 3), and the low bit is the bank number (0 or 1).

Also, bit 0 of $9F25 tells VERA which data port to use (0 or 1). This allows you to quickly flip between two different data addresses, useful for bulk copies or movement of data.

So to write to address $1234, you would:
Set $9F25 to 0 (select data port 0)
Set $9F20 to $34
Set $9F21 to $12
Set $9F22 to 0

Then write data to $9F23.

This will set a single character cell or graphic pixel. If you are writing a horizontal line, setting an increment of 1 (set $9F22 to $1x) will automatically set the address to the next pixel, so you can just keep writing data until you need to change rows.

#include <cx16.h>
#include <peekpoke.h>
/* nope.c */
int main() {
    int i;
    POKE(0x9F25, 0);
    POKE(0x9F20, 0x34);
    POKE(0x9F21, 0x12);
    for (i = 0; i < 1000; i++) {
        POKE(0x9F22, i);
        POKE(0x9F23, i);
    }
    return 0;
}

#include <cx16.h>

/* plotsomehow.c */

/* compilation: 
export CC65_HOME=/usr/share/cc65
cl65 -O -o PL.PRG -t cx16 plotsomehow.c */

#define BLACK 0
#define WHITE 85
#define RED 170
#define CYAN 255

#define WIDTH_BYTES_640_2BPP 640 / 4 // 160

void main() {
    unsigned long tileBaseAddr = 0;
    unsigned short x, y;

    VERA.layer1.config   = 0b00000101;
    VERA.layer1.tilebase = tileBaseAddr >> 9 | 0b1;
    VERA.address         = tileBaseAddr;
    VERA.address_hi      = tileBaseAddr >> 16;
    VERA.address_hi     |= 0b10000;

    for (y=0; y < 480; y++) {
        for (x = 0; x < WIDTH_BYTES_640_2BPP; x++) {
            if (x < 20) {
                VERA.data0 = BLACK;
            }
            if (x >= 20 && x < 40) {
                VERA.data0 = WHITE;
            }
            if (x >= 40 && x < 60) {
                VERA.data0 = RED;
            }
            if (x >= 60 && x < 80) {
                VERA.data0 = CYAN;
            }
        }
    }
}