Board:   [DoveNet] Programming
Subject: DOS EMM calls in a TSR
From:    Jcurtis
Date:    Tue Jun 24, 2025 21:27

By trial and error I discovered EMM calls enable interrupts. This can
cause havoc in a TSR where you need interrupts disabled. Finding these
bugs is not easy. My TSR enables interrupts part of the time, so I do
EMM calls there. Here's an example with comments.

void
next_irq (void)
{
    int x;

  next:
    x = next ();                        /* service IRQs with */
    enable ();                         /* interrupts enabled */

# ifndef noemm                          /* EMM call enables interrupts, do */
    emm_get_page_map (e1);              /* not do it before enable () above */
# endif

    if (x) {
        service_com_irqs (x);

    } else
        service_ticktock ();

# ifndef noemm
    emm_set_page_map (e1);
# endif

    disable ();
    if (x)
    mask_irq (NO, x);

    if (iq[iz])
        goto next;
}

 * SLMR 2.1a *

 * SLMR 2.1a *
---
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