geos.c

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/* Part of the Xemu project, please visit: https://github.com/lgblgblgb/xemu
   Copyright (C)2016-2021 LGB (Gábor Lénárt) <lgblgblgb@gmail.com>
 
   This is an odd emulator, emulating a Commodore 64 like machine only for the
   level needed for a special version of GEOS to be able to run on it.
   You should have a really special one with own disk drive etc, since there
   is no hardware support for drive emulation etc, but it's built in the emulator
   with a kind of CPU trap! The purpose: know GEOS better and slowly replace
   more and more functions on C/emulator level, so at one point it's possible
   to write a very own version of GEOS without *any* previously used code in
   the real GEOS. Then it can be even ported to other architectures GEOS wasn't
   mean to run ever.
   ---------------------------------------------------------------------------------
   One interesting plan: write a GEOS emulator which does not use VIC-II bitmapped
   screen anymore, but the GEOS functions mean to be targeted a "modern UI toolkit",
   ie GTK, so a dozens years old (unmodified) GEOS app would be able to run on a PC
   with modern look and feel, ie anti-aliased fonts, whatever ...
   ---------------------------------------------------------------------------------
 
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
 
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.
 
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
 
#include <stdio.h>
#include <ctype.h>
#include <string.h>
 
#include "xemu/emutools.h"
 
#include "commodore_geos.h"
#include "xemu/cpu65.h"
#include "geos.h"
#include "xemu/emutools_files.h"
 
 
 
 
void inject_screencoded_message ( int addr, const char *s )
{
        while (*s) {
                unsigned char c = (unsigned char)(*(s++));
                if (c >= 65 && c <= 90)
                        c -= 64;
                else if (c >= 97 && c <= 122)
                        c -= 96;
                colour_sram[addr] = 0xF1;
                memory[addr + 0x0400] = c;
                addr++;
        }
}
 
 
 
static int check_basic_stub ( Uint8 *p, int addr )
{
        int a = 10;
        if (*p != 0x9E)
                return -1;      // should be "SYS" token
        p++;
        while (*p == 0x20 && --a)
                p++;
        if (!a)
                return -1;
        DEBUG("OK! %c%c%c%c" NL, p[0], p[1], p[2], p[3]);
        if (
                !isdigit(p[0]) || !isdigit(p[1]) || !isdigit(p[2]) || !isdigit(p[3]) ||
                isdigit(p[4])
        )
                return -1;
        a = (p[0] - '0') * 1000 + (p[1] - '0') * 100 + (p[2] - '0') * 10 + (p[3] - '0');
        if (a < addr + 12 || a > addr + 100)
                return -1;
        DEBUG("GEOS: basic stub SYS address is %d decimal." NL, a);
        return a;
}
 
 
 
int geos_load_kernal ( const char *kernal_image_name )
{
        Uint8 buffer[0xB000];
        int addr, len = xemu_load_file(kernal_image_name, buffer, 0x1000, sizeof buffer, "Cannot load specified GEOS kernal image");
        if (len < 0)
                return 1;
        addr = buffer[0] | (buffer[1] << 8);    // load address
        if (addr == 0x5000) {
                cpu65.pc = 0x5000;
        } else if (addr == 0x801) {
                int sys = check_basic_stub(buffer + 6, addr);
                if (sys < 0) {
                        INFO_WINDOW("Invalid BASIC stub for the GEOS kernal (%s)", xemu_load_filepath);
                        return 1;
                }
                cpu65.pc = sys;
                inject_screencoded_message(6 * 40, "*** Basic stub, you need to wait now ***");
        } else {
                INFO_WINDOW("Invalid GEOS kernal load address ($%04X) in (%s)", addr, xemu_load_filepath);
                return 1;
        }
        // OK. Everything seems to be so okey ...
        memcpy(memory + addr, buffer + 2, len - 2);
        return 0;
}
 
 
void geos_cpu_trap ( Uint8 opcode )
{
        // Hopefully the trap itself is in RAM ..
        DEBUG("GEOS: TRAP-SYM: \"%s\"" NL, memory + cpu65.pc);
        cpu65.pc += strlen((const char*)memory + cpu65.pc) + 1;
}