• C Code Works

    Carver Harrison • 08/31/2020 at 01:19 • 0 comments

    I have successfully gotten a simple program written in C to run. The program prints out a stanza from the poem To a Waterfowl. After each stanza, it waits for user input before printing the next stanza. Source code is shown below:

    void kernel_main(void) {
	while (1) {
		mc6850_print("Whither, 'midst falling dew,\
While glow the heavens with the last steps of day,\
Far, through their rosy depths, dost thou pursue\
Thy solitary way?");
mc6850_read();
mc6850_print("Vainly the fowler’s eye\
Might mark thy distant flight, to do thee wrong,\
As, darkly seen against the crimson sky,\
Thy figure floats along.");
mc6850_read();
mc6850_print("Seek’st thou the plashy brink\
Of weedy lake, or marge of river wide,\
Or where the rocking billows rise and sink\
On the chaféd ocean side?");
mc6850_read();
mc6850_print("There is a Power, whose care\
Teaches thy way along that pathless coast,—\
The desert and illimitable air\
Lone wandering, but not lost.");
mc6850_read();
mc6850_print("All day thy wings have fanned,\
At that far height, the cold thin atmosphere;\
Yet stoop not, weary, to the welcome land,\
Though the dark night is near.");
mc6850_read();
mc6850_print("And soon that toil shall end,\
Soon shalt thou find a summer home, and rest,\
And scream among thy fellows; reeds shall bend,\
Soon, o’er thy sheltered nest.");
mc6850_read();
mc6850_print("Thou’rt gone, the abyss of heaven\
Hath swallowed up thy form, yet, on my heart\
Deeply hath sunk the lesson thou hast given,\
And shall not soon depart.");
mc6850_read();
mc6850_print("He, who, from zone to zone,\
Guides through the boundless sky thy certain flight,\
In the long way that I must trace alone,\
Will lead my steps aright.");
	}
}

     This is what it outputs to the serial terminal:

    I have also completed the MC6850 library. Source code is shown below:
    #define MC6850_BASE 0xC0000

uint8_t* const mc6850_command = (uint8_t*)(MC6850_BASE);
uint8_t* const mc6850_data = (uint8_t*)(MC6850_BASE+1);

char mc6850_read(void) {
    // check if RDR full
    while (!(*mc6850_command & 1));

    // read character from RDR
    return *mc6850_data;
}

void mc6850_write(char c) {
    // check if TDR empty
    while (!(*mc6850_command & 2));

    // write character to TDR
    *mc6850_data = c;
}

void mc6850_print(const char* s) {
    while (*s) mc6850_write(*s++);
} 

  • Exception Handlers

    Carver Harrison • 08/30/2020 at 23:53 • 0 comments

    I have implemented a very simple exception handler so that I can figure out what is causing the machine to fault.


    The exception handler is telling me that the issue is an invalid instruction. It turns out, I forgot to add -march=68000 -mcpu=68000 to the C compiler flags. I added said flags and compared the binaries:
    It turns out that EXTB is a 68020 instruction not present in the 68008. That was what was causing the fault.