Z820 - Z80 Computer

Original post: http://8times8.eeems.me:81/blog/index-beta.php?thread=16

First video of a blinking LED program.


The features:
CPU: Z80 @ 20MHz
RAM: 128k
ROM: 8k (BIOS+BDOS)
UART: Up to 1.25Mb/s transfer rate
FDC: Not implemented yet.

Sourcecode can be found here: https://github.com/keoni29/z820 (unoptimized as all hell, cause I am still learning)

Project page: http://8times8.eeems.me:81/project/software/visicom/

The Visicom is a textphone for deaf people from the 80's. It has a keyboard, video output and built in modem. You could use it as a textphone using the textphone protocol or as a teletype (tty) using the built in modem.

I bought this at a thriftshop because it looked interesting.
I decided to crack it open and find out exactly what makes it tick. Detailed documentation can be found on my project page.


Guts

Left: Video output. You're greeted with a dutch menu. This image shows B&W video, but there is a switch inside the device which enables 8 color video.
Right: Rom reader device I built to dump the firmware. The disassembly can be found here: http://8times8.eeems.me:81/project/software/visicom/disassembly.php

I found an open-source disassembler written in Golang for the tms7001 microcontroller that is inside the visicom, but it was really buggy. I managed to fix a lot of the bugs. I published the disassembled rom on my website. Using javascript I made all addresses operands links so you can jump by clicking them.
Rom disassembly can be found here: http://8times8.eeems.me:81/project/software/visicom/#h2

I am now able to write my own code for the device. So far I can:
- Set up the serial clock generator.
- Control the MCU's internal I/O port.
- Use interrupts
- Read and write data over serial (using the ACIA)
- Read keystrokes from the keyboard

I solved some interrupt problems by looking at the disassembly. It seems like the people who designed this thing ran into the same problems as I did
Next I want to output characters on the screen.

For some reason interrupts don't work the way they used to (or I am just being stupid)
This code is supposed to increment a number on screen once every second, but it doesn't. It just increments T once and then never does the ISR again. Why is that?
.ISR fnInt(msc, 6)
0->T
FnOn
ClrHome
Repeat  getkey(15)
 Output(8,0,T/108>Dec
End
LnReg
Return

Lbl MSC
T++
Return

Has anyone found a way to produce decent soundeffects using interrupts?

I made a test program that generates variable size bmp images. When I generate images with widths under 11 or so the images have weird colors in them at the top.
/*
    Create 24 bit Bitmap image.
    Date: 16 oct 2014
    Version: 1
    Error: Weird colors when making images smaller than ~11 pixels wide.
*/


#include <stdio.h>

/* Write little-endian 32 bit value to file. */
void fputlong(int val, FILE *fp){
    fputc((char)(val & 0xFF), fp);
    fputc((char)((val >> 8 )& 0xFF), fp);
    fputc((char)((val >> 16) & 0xFF), fp);   
    fputc((char)(val >> 24), fp);
}

/*
    argv[1] = char *src;
    argv[2] = char *dst;
*/
int main (int argc, char *argv[]) {
    FILE *dst;
    int ch, padding, xx, yy, w, h;
    char red, green, blue;
    /* Verify user input */
    if (argc < 4) {
        printf("Error: ");
    }
    switch (argc) {
        case 0:
        case 1: printf("Missing filename");
                break;
        case 2: printf("Missing image width");
                break;
        case 3: printf("Missing image height");
                break;
        case 4: printf("Missing RED color value");
                break;
        case 5: printf("Missing GREEN color value");
                break;
        case 6: printf("Missing BLUE color value");
    }
    if (argc < 4) {
        printf("\nUsage: bmptest file.bmp width height r(0-255) g(0-255) b(0-255)\n");   
        return 0;
    }
w = atoi(argv[2]);
    h = atoi(argv[3]);
    red = (char)atoi(argv[4]);
    green = (char)atoi(argv[5]);
    blue = (char)atoi(argv[6]);

    dst = fopen(argv[1], "wb+");

    /* Write file header */
    fputc('B', dst);    // File identifier
    fputc('M', dst);    //
    padding = (4 - ((w * 3) % 4))% 4;
fputlong(w * h * 3 + 50 + (padding * h), dst); // Filesize
    fputlong(0x00, dst);        // Reserved 4 bytes.
    fputlong(0x036, dst);     // Offset
fputlong((int)40,dst);
    fputlong(w, dst);        // Width of bitmap
    fputlong(h, dst);        // Height of bitmap
    fputc(0x01, dst);        // Number of color planes
    fputc(0x00, dst);
    fputc(24, dst);            // Number of bits per pixel
    fputc(0x00, dst);
    fputlong(0x00, dst);    // Compression method: none
    fputlong(0x00, dst);    // Image size. Dummy 0
    fputlong(0x2700, dst);    // Horizontal resolution
    fputlong(0x2700, dst);    // Vertical resolution
    fputlong(0x00, dst);    // Number of colors in palette (Default 2^n)
    fputlong(0x00, dst);    // All colors are equally important
    for (yy = 0; yy < h; yy ++) {
        for (xx = 0; xx < w; xx ++) {
fputc(blue, dst);
fputc(green, dst);
fputc(red, dst);
        }
for (xx = 0; xx < padding; xx ++) {
fputc(0x00, dst);
}
    }
    printf("Padding = %d; Filesize = %d\n", padding , w * h * 3 + 50 + (padding * h));
    fclose(dst);
    return 0;
}Is this a problem with my code or with the decoder?
My bad. Padding should be at the end of every row of pixels >.<

The ipv4 version of the internet counts 2^32 individual addresses. I decided to ping all of them, wait for a response and if I get one: log that to a file.

I wrote a script that does this for me. If I run 256 instances of this script simultaneously I can ping the whole internet in about 10 days.
Just some logfiles are not super interesting to watch, but once you convert them into an image it becomes a lot more interesting. This is a test image I generated using the data from the 83.xx.xx.xx range. Each pixel represents a block of 256 ip addresses. The color is determined by how many devices responded in the block.

Pinged all addresses in the 83.xx.xx.xx range:

It takes about 1 hour to generate a picture like this. I will release the source once it's done

Should everyone learn how to code? Everyone walks around with computers in their pockets, but nobody knows what makes these devices tick. People don't know where software comes from anymore. When something has blinky lights and beepy sounds it's cool, but if it calculates the square root of pi in a 20 byte program it's... interesting I guess?

What are your opinions?

Building a giant rugged laptop. Specs: Celeron D cpu, 2GB ram, Dual boot WinXP Xubuntu on 200GB hdd
Most importantly: full keyboard.

I intend to use this thing outdoors.

Image is clicky