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core: Add framework for an FPU

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This adds the skeleton of a floating-point unit and implements the
mffs and mtfsf instructions.

Execute1 sends FP instructions to the FPU and receives busy,
exception, FP interrupt and illegal interrupt signals from it.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This commit is contained in:
Paul Mackerras
2020-08-28 20:01:00 +10:00
parent 76ec1a2f0a
commit 856e9e955f
11 changed files with 417 additions and 33 deletions
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27
writeback.vhdl
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@@ -12,6 +12,7 @@ entity writeback is
e_in : in Execute1ToWritebackType;
l_in : in Loadstore1ToWritebackType;
fp_in : in FPUToWritebackType;
w_out : out WritebackToRegisterFileType;
c_out : out WritebackToCrFileType;
@@ -31,15 +32,21 @@ begin
-- Do consistency checks only on the clock edge
x(0) := e_in.valid;
y(0) := l_in.valid;
assert (to_integer(unsigned(x)) + to_integer(unsigned(y))) <= 1 severity failure;
w(0) := fp_in.valid;
assert (to_integer(unsigned(x)) + to_integer(unsigned(y)) +
to_integer(unsigned(w))) <= 1 severity failure;
x(0) := e_in.write_enable or e_in.exc_write_enable;
y(0) := l_in.write_enable;
assert (to_integer(unsigned(x)) + to_integer(unsigned(y))) <= 1 severity failure;
w(0) := fp_in.write_enable;
assert (to_integer(unsigned(x)) + to_integer(unsigned(y)) +
to_integer(unsigned(w))) <= 1 severity failure;
w(0) := e_in.write_cr_enable;
x(0) := (e_in.write_enable and e_in.rc);
assert (to_integer(unsigned(w)) + to_integer(unsigned(x))) <= 1 severity failure;
y(0) := fp_in.write_cr_enable;
assert (to_integer(unsigned(w)) + to_integer(unsigned(x)) +
to_integer(unsigned(y))) <= 1 severity failure;
end if;
end process;
@@ -53,7 +60,7 @@ begin
c_out <= WritebackToCrFileInit;
complete_out <= '0';
if e_in.valid = '1' or l_in.valid = '1' then
if e_in.valid = '1' or l_in.valid = '1' or fp_in.valid = '1' then
complete_out <= '1';
end if;
@@ -79,6 +86,18 @@ begin
c_out.write_xerc_data <= e_in.xerc;
end if;
if fp_in.write_enable = '1' then
w_out.write_reg <= fp_in.write_reg;
w_out.write_data <= fp_in.write_data;
w_out.write_enable <= '1';
end if;
if fp_in.write_cr_enable = '1' then
c_out.write_cr_enable <= '1';
c_out.write_cr_mask <= fp_in.write_cr_mask;
c_out.write_cr_data <= fp_in.write_cr_data;
end if;
if l_in.write_enable = '1' then
w_out.write_reg <= l_in.write_reg;
w_out.write_data <= l_in.write_data;