cores
/
microwatt
mirror of https://github.com/antonblanchard/microwatt
3
1
Fork 1
Code Issues Projects Releases Wiki Activity

execute1: Use truth table embedded in instruction for CR logical ops

Browse Source 
It turns out that CR logical instructions have the truth table of
the operation embedded in the instruction word.  This means that we
can collect the two input operand bits into a 2-bit value and use
that as the index to select the appropriate bit from the instruction
word.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
pull/153/head
Paul Mackerras 5 years ago
parent a2bf039a70
commit 441160d865
1 changed files with 5 additions and 21 deletions
Show Stats Download Patch File Download Diff File

26
execute1.vhdl
Unescape Escape View File

@ -200,6 +200,7 @@ begin
variable bo, bi : std_ulogic_vector(4 downto 0); variable bo, bi : std_ulogic_vector(4 downto 0);
variable bf, bfa : std_ulogic_vector(2 downto 0); variable bf, bfa : std_ulogic_vector(2 downto 0);
variable cr_op : std_ulogic_vector(9 downto 0); variable cr_op : std_ulogic_vector(9 downto 0);
variable cr_operands : std_ulogic_vector(1 downto 0);
variable bt, ba, bb : std_ulogic_vector(4 downto 0); variable bt, ba, bb : std_ulogic_vector(4 downto 0);
variable btnum, banum, bbnum : integer range 0 to 31; variable btnum, banum, bbnum : integer range 0 to 31;
variable crresult : std_ulogic; variable crresult : std_ulogic;
@ -532,27 +533,10 @@ begin
btnum := 31 - to_integer(unsigned(bt)); btnum := 31 - to_integer(unsigned(bt));
banum := 31 - to_integer(unsigned(ba)); banum := 31 - to_integer(unsigned(ba));
bbnum := 31 - to_integer(unsigned(bb)); bbnum := 31 - to_integer(unsigned(bb));
case cr_op(8 downto 5) is -- Bits 5-8 of cr_op give the truth table of the requested
when "1001" => -- CREQV -- logical operation
crresult := not(e_in.cr(banum) xor e_in.cr(bbnum)); cr_operands := e_in.cr(banum) & e_in.cr(bbnum);
when "0111" => -- CRNAND crresult := cr_op(5 + to_integer(unsigned(cr_operands)));
crresult := not(e_in.cr(banum) and e_in.cr(bbnum));
when "0100" => -- CRANDC
crresult := (e_in.cr(banum) and not e_in.cr(bbnum));
when "1000" => -- CRAND
crresult := (e_in.cr(banum) and e_in.cr(bbnum));
when "0001" => -- CRNOR
crresult := not(e_in.cr(banum) or e_in.cr(bbnum));
when "1101" => -- CRORC
crresult := (e_in.cr(banum) or not e_in.cr(bbnum));
when "0110" => -- CRXOR
crresult := (e_in.cr(banum) xor e_in.cr(bbnum));
when "1110" => -- CROR
crresult := (e_in.cr(banum) or e_in.cr(bbnum));
when others =>
crresult := '0';
report "BAD CR?";
end case;
v.e.write_cr_mask := num_to_fxm((31-btnum) / 4); v.e.write_cr_mask := num_to_fxm((31-btnum) / 4);
for i in 0 to 31 loop for i in 0 to 31 loop
if i = btnum then if i = btnum then

Write Preview
Loading…
Cancel
Save