• C Code Works

    Carver Harrison08/31/2020 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_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_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_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_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_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_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_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 Harrison08/30/2020 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.