W I S C H N E R

Let us compile'n'run stuff.

In part I. of this turorial you "gitted" yx repository to your local disk. If you followed the tutorial then your target folder was ~/dev/yx.

Open the terminal and set this as your current working folder. Go to tools subfolder (e.g. execute cd ~/dev/yx/tools). There are a bunch of useful tools inside but right now we are only interested in makezxbin. This is an upgraded makebin tool that enables us to use SDCC C compiler for ZX Spectrum development.

You are free to choose z88dk instead. But SDCC is -in my opinion- a more mature environment. It supports C99; has as advanced code optimizer; and produces gdb-z80 compatible symbolic information. z88dk on the other side has superior libraries and ZX Spectrum support.

You can compile and deploy makezxbin like this:

cd makezxbin
gcc makezxbin.c -o makezxbin
sudo mv makezxbin /usr/bin/makezxbin

Congratulations! You now have a complete suite of compiler tools needed to develop for ZX Spectrum.

Now go to the ~/dev/yx/apps/template folder and run make. This will create a template application which writes a value of 255 to the first byte of video memory. When it is run the result will be 8 pixel line in the first row of the screen:

The make file will also run the emulator and load your app.

You can use this template application as a quick starter for most of your development projects. Let's analyse it.

First there is a pretty straightforward Makefile. Its main target is app.bin. The Makefile assumes that all *.c files ald all *.s files are part of our project. Thus if you add new source files - it will automatically consume them as part of our project.

For easier understanding here are the unconventional tricks of this Makefile:

• it uses your standard gcc (and not SDCC!) compiler to generate .depend file out of *.c and *.h source files for easier compilation,
• it puts crt0.s to 0x8000 and your program to 0x8032, so if you change crt0.s (increasing its length above 0x32 bytes) make sure you update your programs' start address,
• it uses our makezxbin tool to generate correct binary (makebin has a bug and can't be used for this purpose), and
• it uses SDCC all the way but at the end executes appmake +zx --binfile ./app.bin --org 32768 to generate ZX Spectrum tape. appmake is part of z88dk and this is one reason installing both development environments in part I. of this tutorial.

The other two files in the folder are crt0.s and app.c  crt0.s is a standard name for a startup file t.i. a file that gets executed first when your program is stasrted.  This one prepares everything to run your program from BASIC and return control to it. It:

• stores current stack pointer and contents of all registers,
• jumps to start of GSINIT assembler section where the SDCC compiler places all global variables initialization code,
• establishes stack (1KB) and heap global symbols for our program,
• jumps to _main C function, and
• when the main concludes restores registers and stack and returns control to BASIC.

crt0.s is compiled to address 32768 (0x8000) and is 0x32 bytes long. app.c code is compiled to the address 0x8032. It contains the main function.  This function simply writes 255 to the first video memory byte:

void main() {
    unsigned char * vmem = 16384;
    (*vmem)=255;
}

You can examine the locations of your symbols (variables, functions) by opening crt0.map file after compilation.

That's it for yoday. Enjoy your experimenting. Our next tutorial will be about debugging.