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added register stage to PMP mask computation to shorten PMP's critical path

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stnolting 2020-07-30 21:06:39 +02:00
parent 8f0cd29b2c
commit aab978a625
1 changed files with 13 additions and 11 deletions
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24
rtl/core/neorv32_cpu_bus.vhd
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@ -413,18 +413,20 @@ begin
-- Physical Memory Protection (PMP) -------------------------------------------------------
-- -------------------------------------------------------------------------------------------
-- compute address masks --
pmp_masks: process(pmp_addr_i)
pmp_masks: process(clk_i)
begin
for r in 0 to PMP_NUM_REGIONS-1 loop -- iterate over all regions
pmp.addr_mask(r) <= (others => '0'); -- default
for i in PMP_GRANULARITY+1 to 33 loop
if (i = PMP_GRANULARITY+1) then
pmp.addr_mask(r)(i) <= '0';
else -- current bit = not AND(all previous bits)
pmp.addr_mask(r)(i) <= not (and_all_f(pmp_addr_i(r)(i-1 downto PMP_GRANULARITY)));
end if;
end loop; -- i
end loop; -- r
if rising_edge(clk_i) then -- address configuration (not the actual address check!) has a latency of +1 cycles
for r in 0 to PMP_NUM_REGIONS-1 loop -- iterate over all regions
pmp.addr_mask(r) <= (others => '0'); -- default
for i in PMP_GRANULARITY+1 to 33 loop
if (i = PMP_GRANULARITY+1) then
pmp.addr_mask(r)(i) <= '0';
else -- current bit = not AND(all previous bits)
pmp.addr_mask(r)(i) <= not (and_all_f(pmp_addr_i(r)(i-1 downto PMP_GRANULARITY)));
end if;
end loop; -- i
end loop; -- r
end if;
end process pmp_masks;