all repos — xyw @ b7653c327150ccaf56ab6990290b9f2f1e0f4c18

A minimal virtual machine and assembler for terminals.

devices/system.c

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#include <time.h>
#include <stdlib.h>
#include <stdio.h>
#include "../xyw.h"

#define SYSTEM_STATE 0x00
#define SYSTEM_ERROR 0x01
#define SYSTEM_PAGE 0x02
#define SYSTEM_RANDOM 0x03
#define SYSTEM_ON_ERROR 0x04
#define SYSTEM_IMAGE_EXEC 0x06

#define SYSTEM_STATE_RUNNING 0x01
#define SYSTEM_STATE_ERROR 0x80

#define XYW_ERROR_NONE 0

/// Error handler tracking (accessible by xywrun.c for snapshot/reset)
xyw_byte error_handler_entry_s = 0;

void system_setup(xyw_byte *data)
{
    (void)data;
    srand(time(NULL));
    error_handler_entry_s = 0;
}

xyw_byte system_input(xyw_byte *data, xyw_byte addr, xyw_byte *error)
{
    if (addr == SYSTEM_RANDOM)
        return (xyw_byte)(rand() & 0xFF);
    (void)error;
    return data[addr];
}

void system_output(xyw_byte *data, xyw_byte addr, xyw_byte *error)
{
    (void)error;
    if (addr == SYSTEM_IMAGE_EXEC + 1)
    {
        xyw_word target = XYW_PEEKW(&data[SYSTEM_IMAGE_EXEC]);
        if (target != 0)
            xyw_request_exec(target);
    }
}

void system_tick(xyw_byte *data)
{
    // Check if returning from error handler (after RTS popped the frame)
    if ((data[SYSTEM_STATE] & SYSTEM_STATE_ERROR) &&
        error_handler_entry_s != 0 &&
        xyw_vm_get_system_depth() == error_handler_entry_s)
    {
        data[SYSTEM_STATE] &= ~SYSTEM_STATE_ERROR;
        error_handler_entry_s = 0;
    }

    // Check for new error condition
    if (data[SYSTEM_ERROR] != XYW_ERROR_NONE && !(data[SYSTEM_STATE] & SYSTEM_STATE_ERROR))
    {
        xyw_word on_error_handler = XYW_PEEKW(&data[SYSTEM_ON_ERROR]);
        if (on_error_handler != 0)
        {
            XYW_DBG("Error occurred: %02X, jumping to error handler at %04X\n", data[SYSTEM_ERROR], on_error_handler);
            data[SYSTEM_STATE] |= SYSTEM_STATE_ERROR;
            error_handler_entry_s = xyw_vm_get_system_depth();
            xyw_vm_push_frame(*pc);
            *pc = on_error_handler;
        }
        else
        {
            // No error handler: halt execution
            data[SYSTEM_STATE] &= ~SYSTEM_STATE_RUNNING;
        }
    }
}