DSPHLE MailHandler: Synchronize reads and interrupts

This change is meant to solve the following problem: how to translate the
following snippet to DSPHLE:
    SendInterruptAndWaitRead(MAIL_A);
    SendAndWaitRead(MAIL_B);

    SendInterruptAndWaitRead(MAIL_C);

This should cause the following actions on the CPU side:
    ---> Woken up by interrupt
    Reads MAIL_A
    Reads MAIL_B
    <--- Exits interrupt handler

    ---> Woken up by interrupt
    Reads MAIL_C
    <---

But with the current DSPHLE mail support, the following would happen because
the "AndWaitRead" part is not supported:
    ---> Woken up by interrupt
    Reads MAIL_A
    Reads MAIL_B
    <--- Exits interrupt handler

    [Never gets the second interrupt since it was triggered at the same time as
    the first one! Misses MAIL_C.]

This changes fixes the issue by storing two values in the mail queue on the DSP
side: the value of the mail itself, and whether a read of that mail should
trigger a DSP interrupt. If nothing is in the queue yet and an interrupt is
requested, just trigger the interrupt. In the present example, the queue will
look like this:
    Mail value       Interrupt requested
     MAIL_A                  No           <-- Interrupt was triggered when
                                              pushing the mail to the queue.
     MAIL_B                  Yes
     MAIL_C                  No

When the CPU will read MAIL_B, this will cause MailHandler to trigger the
interrupt, which will be handled by the CPU when coming back from the exception
handler. MAIL_C is then successfully read.

0 files changed, 0 insertions, 0 deletions