2 Feb
2022
2 Feb
'22
2:25 a.m.
On Feb 1, 2022, at 7:27 PM, Johnny Billquist
<bqt(a)softjar.se> wrote:
By the way, I do agree that it looks like you spotted the problem, in that the KG11 seems
to just do a single cycle when it should process a word. Now you just need to figure out
why it goes wrong in that way. :-)
Johnny
I think I see the problem, but how the KG11 diagnostic can pass at all is quite beyond
comprehension.
In the data register write, the emulation clears the DONE flag, then if SEN (shift enable)
is set, it begins the checksum update. In normal mode (not single step) it loops on the
"do a step" operation until DONE is set again.
So far so good.
How does DONE get set? In function cycleOneBit, an internal counter PULSCNT is compared
with the count that belongs to the currently configured mode: 6, 8, 12 or 16 depending on
the polynomial. When PULSCNT reaches the limit (more precisely, when it is >= the
limit) DONE is set.
The trouble is that PULSCNT is cleared only by reset and by status register write. It is
NOT reset at the end of a normal byte or word operation. That means that every operation
after the first one will only do one bit, unless the host writes SR after each byte or
word.
The solution seems to be to add a clear of PULSCNT after a byte or word has been
consumed:
static void do_poly (int unit, t_bool step)
{
if (kg_unit[unit].SR & KGSR_M_DONE)
return;
if (step)
cycleOneBit (unit);
else {
while (!(kg_unit[unit].SR & KGSR_M_DONE))
cycleOneBit (unit);
kg_unit[unit].PULSCNT = 0; /* *** ADDED *** */
}
}
paul