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<DIV dir=ltr align=left><SPAN class=792354521-11122010><FONT color=#0000ff
size=2 face=Arial>I was not defending the simh code, and agree that it does not
conform. </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=792354521-11122010><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=792354521-11122010><FONT color=#0000ff
size=2 face=Arial>Interestingly, a version of altair_cpu.c c.a. 2003 seems to be
more correct, so it appears that some "code cleanup" introduced this form of the
bug at a later date. The old code still wasn't correct, as it
didn't clear AC if the add is NOT done...</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=792354521-11122010><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=792354521-11122010><FONT color=#0000ff
size=2 face=Arial>Obviously this needs a regression test!</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=792354521-11122010><SPAN lang=EN>
<P><FONT size=2 face="Courier New">case 047: { /* DAA */</FONT></P>
<P><FONT size=2 face="Courier New">DAR = A & 0x0F;</FONT></P>
<P><FONT size=2 face="Courier New">if (DAR > 9 || AC > 0) {</FONT></P>
<P><FONT size=2 face="Courier New">DAR += 6;</FONT></P>
<P><FONT size=2 face="Courier New">A &= 0xF0;</FONT></P>
<P><FONT size=2 face="Courier New">A |= DAR & 0x0F;</FONT></P>
<P><FONT size=2 face="Courier New">if (DAR & 0x10)</FONT></P>
<P><FONT size=2 face="Courier New">AC = 0200000;</FONT></P>
<P><FONT size=2 face="Courier New">else</FONT></P>
<P><FONT size=2 face="Courier New">AC = 0;</FONT></P>
<P><FONT size=2 face="Courier New">}</FONT></P>
<P><FONT size=2 face="Courier New">DAR = (A >> 4) & 0x0F;</FONT></P>
<P><FONT size=2 face="Courier New">if (DAR > 9 || AC > 0) {</FONT></P>
<P><FONT size=2 face="Courier New">DAR += 6;</FONT></P>
<P><FONT size=2 face="Courier New">if (AC) DAR++;</FONT></P>
<P><FONT size=2 face="Courier New">A &= 0x0F;</FONT></P>
<P><FONT size=2 face="Courier New">A |= (DAR << 4);</FONT></P>
<P><FONT size=2 face="Courier New">}</FONT></P>
<P><FONT size=2 face="Courier New">if ((DAR << 4) & 0x100)</FONT></P>
<P><FONT size=2 face="Courier New">C = 0200000;</FONT></P>
<P><FONT size=2 face="Courier New">else</FONT></P>
<P><FONT size=2 face="Courier New">C = 0;</FONT></P>
<P><FONT size=2 face="Courier New">if (A & 0x80) {</FONT></P>
<P><FONT size=2 face="Courier New">S = 0200000;</FONT></P>
<P><FONT size=2 face="Courier New">} else {</FONT></P>
<P><FONT size=2 face="Courier New">S = 0;</FONT></P>
<P><FONT size=2 face="Courier New">}</FONT></P>
<P><FONT size=2 face="Courier New">if ((A & 0xff) == 0)</FONT></P>
<P><FONT size=2 face="Courier New">Z = 0200000;</FONT></P>
<P><FONT size=2 face="Courier New">else</FONT></P>
<P><FONT size=2 face="Courier New">Z = 0;</FONT></P>
<P><FONT size=2 face="Courier New">parity(A);</FONT></P>
<P><FONT size=2 face="Courier New">A = A & 0xFF;</FONT></P>
<P><FONT size=2 face="Courier New">break;</FONT></P>
<P><FONT size=2 face="Courier New">}</FONT></P></SPAN></SPAN></DIV><!-- Converted from text/plain format --><BR>
<P><FONT
size=2>---------------------------------------------------------<BR>This
communication may not represent my employer's views,<BR>if any, on the matters
discussed.<BR> </FONT> </P>
<DIV> </DIV><BR>
<DIV dir=ltr lang=en-us class=OutlookMessageHeader align=left>
<HR tabIndex=-1>
<FONT size=2 face=Tahoma><B>From:</B> Al Williams [mailto:al.williams@awce.com]
<BR><B>Sent:</B> Saturday, December 11, 2010 12:08<BR><B>To:</B> Timothe
Litt<BR><B>Cc:</B> Richard Cini; simh@trailing-edge.com; Vince
Briel<BR><B>Subject:</B> Re: [Simh] DAA Emulation<BR></FONT><BR></DIV>
<DIV></DIV>I agree with your interpretation and by that interpretation the code
in both emulators is currently busted. In the case of SIMH adding 6 does not
always result in a half carry.
<DIV><BR></DIV>
<DIV>Granted if LSD is >9 it will cause AC to set. But in the case when AC is
already set this isn't always the case. Assuming the last add was BCD you could
have X9+Y9 = [X+Y+1]2.</DIV>
<DIV><BR></DIV>
<DIV>So the LSD is 2 and AC is set. Adding 6 gives you 8 and no half carry. So
setting the flag every time you add 6 is incorrect.</DIV>
<DIV><BR><BR>
<DIV class=gmail_quote>On Sat, Dec 11, 2010 at 10:51 AM, Timothe Litt <SPAN
dir=ltr><<A href="mailto:litt@ieee.org">litt@ieee.org</A>></SPAN>
wrote:<BR>
<BLOCKQUOTE
style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex"
class=gmail_quote>
<DIV>
<DIV dir=ltr align=left><SPAN><FONT color=#0000ff size=2 face=Arial>According
to the Sep 75 Intel 8080 Microcomputer Systems manual:</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN><FONT color=#0000ff size=2
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN><FONT color=#0000ff size=2 face=Arial>P 4-3:
Auxiliary Carry: If the instruction caused a carry out of bit 3 and into bit 4
of the resulting value, the auxiliary carry is set; otherwise it is
reset. This flag is affected by single precision additions,
subtractions, increments, decrements, comparisons and logical operations, but
is principally used with additions and increments preceding a DAA (Decimal
Adjust Accumulator) instruction.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN><FONT color=#0000ff size=2
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN><FONT color=#0000ff size=2 face=Arial>P 4-8: DAA
description has the text previously cited, plus</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN> <FONT color=#0000ff size=2
face=Arial>NOTE: All flags are affected</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN> <FONT color=#0000ff size=2
face=Arial>Cycles: 1</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN> <FONT color=#0000ff size=2
face=Arial>States: 4</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN> <FONT color=#0000ff size=2
face=Arial>Flags: Z,S,P,CY,AC</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN><FONT color=#0000ff size=2
face=Arial></FONT></SPAN> </DIV>
<DIV><FONT color=#0000ff size=2 face=Arial><SPAN>I read this as AC should
be set if the first add 6 (to the LSB of A) happened and caused a carry and
should be cleared otherwise. (Only this add can cause a carry from bit 3
to bit 4.)</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial></FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial></FONT> </DIV>
<DIV><FONT color=#0000ff size=2 face=Arial></FONT><BR></DIV>
<P><FONT
size=2>---------------------------------------------------------<BR>This
communication may not represent my employer's views,<BR>if any, on the matters
discussed.<BR> </FONT> </P>
<DIV> </DIV><BR>
<DIV dir=ltr lang=en-us align=left>
<HR>
<FONT size=2 face=Tahoma><B>From:</B> <A
href="mailto:simh-bounces@trailing-edge.com"
target=_blank>simh-bounces@trailing-edge.com</A> [mailto:<A
href="mailto:simh-bounces@trailing-edge.com"
target=_blank>simh-bounces@trailing-edge.com</A>] <B>On Behalf Of </B>Al
Williams<BR><B>Sent:</B> Saturday, December 11, 2010 10:30<BR><B>To:</B>
Richard Cini<BR><B>Cc:</B> <A href="mailto:simh@trailing-edge.com"
target=_blank>simh@trailing-edge.com</A>; Vince Briel<BR><B>Subject:</B> Re:
[Simh] DAA Emulation<BR></FONT><BR></DIV>
<DIV>
<DIV></DIV>
<DIV class=h5>
<DIV></DIV>Yeah I've read the docs, but even what you pasted in doesn't
directly answer the question: What is the state of the AC flag after a DAA? So
I think the code correctly implements the additions you mentioned. But I think
we all 3 disagree on the AC flag code. Notice I didn't copy the whole function
in either case, so the handling of the MSD is "not shown".
<DIV><BR></DIV>
<DIV><BR>
<DIV><BR><BR>
<DIV class=gmail_quote>On Sat, Dec 11, 2010 at 8:16 AM, Richard Cini <SPAN
dir=ltr><<A href="mailto:rich.cini@verizon.net"
target=_blank>rich.cini@verizon.net</A>></SPAN> wrote:<BR>
<BLOCKQUOTE
style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex"
class=gmail_quote>
<DIV><FONT face="Calibri, Verdana, Helvetica, Arial"><SPAN
style="FONT-SIZE: 11pt">Al --<BR><BR> Thanks a lot
for the email. I’m sure you looked at this, but I pulled the Intel 8080
Users Manual and under DAA, it says the following (snipping a
bit):<BR><BR> The 8-bit number in the accumulator is
adjusted to form two 4-bit [BCD] digits by the following
process:<BR><BR> (1) If the
value of the least significant 4 bits is greater than 9 <B>or </B>if the AC
flag is set, 6 is added to the
accumulator.<BR> (2) if the
value of the most significant 4 bits is <B>now </B>greater than 9 <B>or
</B>if the CY flag is set, 6 is added to the most significant 4 bits of the
accumulator.<BR><BR> Based on this, I would say that
the second part of the test in the Altair32 code is wrong. Further, it looks
like the SIMH code may be wrong as well because it doesn’t test the CY flag
in the second test.<BR><BR> As far as the register
display, I’ll make that change — oddly no one has ever reported
it.<BR><BR> Thanks again for locating this
bug.<BR><BR>Rich<BR><FONT color=#888888><BR>--<BR>Rich Cini<BR>Collector of
Classic Computers<BR>Build Master and lead engineer, Altair32 Emulator<BR><A
href="http://www.altair32.com"
target=_blank>http://www.altair32.com</A><BR><A
href="http://www.classiccmp.org/cini"
target=_blank>http://www.classiccmp.org/cini</A></FONT>
<DIV>
<DIV></DIV>
<DIV><BR><BR><BR><BR>On 12/11/10 1:32 AM, "Al Williams" <<A
href="http://al.williams@awce.com"
target=_blank>al.williams@awce.com</A>>
wrote:<BR><BR></DIV></DIV></SPAN></FONT>
<DIV>
<DIV></DIV>
<DIV>
<BLOCKQUOTE><FONT face="Calibri, Verdana, Helvetica, Arial"><SPAN
style="FONT-SIZE: 11pt">Hi Rich and Bob,<BR><BR>I've been doing some work
on Vince Briel's excellent AVR emulation of the 8080 and while rewriting
DAA I came across what I think to be a harmless bug but thought you might
want to comment on it.<BR><BR>>From what I can glean DAA effects all
flags including half carry. And I _think_ that half carry occurs from the
+6 (if it happens at all). So if you don't adjust the LSD you get AC=0. If
you add 6 then if adding the 6 gives you a carry out of Bit 3 you get AC
set. Note that the carry might ripple so that's NOT to say Bit 4 is
necessarily 1.<BR><BR>Here's part of Altair32's code:<BR><BR>static void
daa ( OP_ARG_U ) <BR>{<BR>// Decimal Adjust Accumulator<BR>// DAA::
A=BCD format<BR>// Flags: SZAPC<BR>// *****<BR><BR>register /* FJS */ word
tmp = ACCUM;<BR><BR>if ( (( tmp & 0x0f ) > 0x09 ) || ( FLAGS &
AC_FLAG ))<BR>tmp += 0x06;<BR><BR>if (tmp > 0x0f)<BR>FLAGS |= AC_FLAG;
// if adjusted LSB > 0xf, set AC<BR>else<BR>FLAGS &= ~AC_FLAG; //
else clear SC <BR><BR><BR>So since tmp is not masked off, any value
>0xF gets AC set even if no carry or add occurred! In other words,
pretend the value of ACCUM is 90 (and thus temp is 90) with AC=0. The
first if does not fire. The second if does and AC gets set. That's got to
be wrong. Granted, who checks AC after DAA? But
still.... <BR><BR><BR>So why copy Bob? Well... I think SIMH has a
similar but different problem. Here's a snip from the DAA
code:<BR><BR>/*opcode=0x27*/<BR>static void i86op_daa(PC_ENV
*m)<BR>{<BR> uint16 dbyte;<BR> dbyte =
m->R_AL;<BR> if (ACCESS_FLAG(m,F_AF)|| (dbyte&0xf) >
9)<BR> {<BR> dbyte +=
6;<BR> if (dbyte&0x100)<BR>
SET_FLAG(m, F_CF);<BR> SET_FLAG(m,
F_AF);<BR> }<BR> else<BR><BR><BR>Here we
add 6 to dbyte and then AC is always set. If no +6 then AC is cleared.
This COULD be correct behavior, but I can't find any reference material
that says it is. In any event, SIMH and Altair32 are doing something
different here, so they both can't be right. Meanwhile I have my own
version of DAA in AVR assembler that I will spare you unless you ask. The
only real silicon I have even close to operational at the moment is a Z80
and not only is it not operational, the DAA is one place where it is a lot
different so I don't trust the result there.<BR><BR>Oh. One other note
about Altair32. In the debugger, the A and FLAGS display is swapped in the
debug console window. The Register display up top left is ok though. I bet
you've heard that one before.<BR><BR>If either of you can show
documentation on the AC flag after DAA or point to a real piece of
silicon's behavior I'd like to know so I can fix the DAA code in the Briel
emulator to match. Otherwise, I thought you'd like to know about this bug
even though it is pretty innocuous as far as I can tell.<BR><BR><BR>Al
Williams<BR><A href="http://www.ddj.com/embedded"
target=_blank>http://www.ddj.com/embedded</A> (among
others)<BR><BR><BR><BR><BR></SPAN></FONT></BLOCKQUOTE></DIV></DIV></DIV></BLOCKQUOTE></DIV><BR></DIV></DIV></DIV></DIV></DIV></BLOCKQUOTE></DIV><BR></DIV></BODY></HTML>