Flags not set properly after DAA

[Dinesh Sharma]

Flags are not being set properly after DAA. Consider the following code:
MVI A, 099H
ADI 01H
DAA
after this, the result should be 00 with carry set, which it is. However, the sign flag is set and Zero flag is cleared. It should be the other way round. The bug is perhaps caused by setting these flag before doing the final DAA adjustments, when the result was 9A, which would set the sign flag and clear the Z flag. After correction, the result is 00, so sign flag should be cleared, while the Z flag should be set.

[Debjit Biswas (debjitbis08)]

I believe the below code, which is part of the DAA instruction code is the reason for this bug:

  if (sys.reg.a > 0x99 || sys.flag.c)
  {
    sys.reg.a = sys.reg.a + 0x60;
    sys.flag.c = 1;
  }

After this operation there are no statements to modify the flags. When this condition is not activated the function _eef_inst_func_add_i is called which in turn calls the _eef_find_and_set_flags function and thus there is no issues.

It should have been something like this:

  if (sys.reg.a > 0x99 || sys.flag.c)
  {
    sys.reg.a = sys.reg.a + 0x60;
    sys.flag.c = 1;
    _eef_find_and_set_flags (sys.reg.a);
  }

[Dinesh Sharma (iitdinesh)]

In fact, I had reached the same conclusion and added the call to the code and recompiled gnusim8085. This solved the problem.

However, it is my impression that sufficient attention has not been paid to flag setting. I think the dcr instruction should set all flags except carry. I find that it is not setting the auxiliary carry flag. On the other hand, inr does set ac, as required. Since updates to gnusim8085 are so infrequent, we should start releasing versions with bugfixes with a minor version number changed. I shall be happy to test the programme and offer bug fixes when I can.