github.com/livingcomputermuseum.pdp7-unix
1
0
Fork 0
mirror of https://github.com/livingcomputermuseum/pdp7-unix.git synced 2026-02-10 10:20:38 +00:00
Code Issues Releases Wiki Activity

I've added the idiv and mul instructions which are needed by the original PDP-7.

Browse Source 
However, these are completely untested at the present!
This commit is contained in:
Warren Toomey
2016-03-04 15:15:57 +10:00
parent 575163a35a
commit 807fb56d35
1 changed files with 39 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

39
tools/a7out
View File

@@ -487,6 +487,16 @@ sub eae {
my $step = $instruction & EAESTEP;
my $maskedinstr = $instruction & EAEIMASK;
if ( $instruction == 0653323 ) { # idiv: integer division
my $divisor= $Mem[ $PC+1 ];
# Prevent division by zero :-)
my $quotient = ($divisor) ? $AC / $divisor : 0;
my $remainder = ($divisor) ? $AC % $divisor : 0;
$MQ= $quotient;
$AC= $remainder;
$PC+=2;
return;
}
if ( $maskedinstr == 0660500 ) { # lrss: long right shift, signed
# We ignore the MQ as it's not
# used by any user-mode programs
@@ -540,6 +550,35 @@ sub eae {
$PC++;
return;
}
if ( $instruction == 0653122 ) { # mul: unsigned multiply
# This logic shamelessly borrowed from SimH
# https://github.com/simh/simh/blob/master/PDP18B/pdp18b_cpu.c
my $MB= $Mem[ $PC+1 ];
my $eae_ac_sign;
if (($instruction & 0004000) && ($AC & SIGN)) { # IR<6> and minus?
$eae_ac_sign = $LINK; # set eae_ac_sign
} else {
$eae_ac_sign = 0; # if not, unsigned
}
$MQ = $MQ ^ MAXINT if ($eae_ac_sign); # EAE AC sign? ~MQ
my $oldlink= $LINK;
$LINK = 0; # Clear link
foreach my $SC (1 .. $instruction & 077) { # Loop for SC times
$AC = $AC + $MB
if ($MQ & 1); # MQ<17>? add
$MQ = ($MQ >> 1) | (($AC & 1) << 17);
$AC = $AC >> 1; # Shift AC'MQ right
}
if ($eae_ac_sign ^ $oldlink) { # Result negative?
$AC = $AC ^ MAXINT;
$MQ = $MQ ^ MAXINT;
}
$PC++;
return;
}
printf( STDERR "PC %06o: Unknown eae instruction %06o\n",
$PC, $instruction );
exit(1);