Kontron COMe Starterkit Eval T2 - Manual (Page 210)

Appendix B: Sourcecode for Port 80 Decoder
---------------------------------------------------------------------------
-- LPC state machine
-- LPC_State value is actually one clock cycle late.
---------------------------------------------------------------------------
P_LPC_StatMachine: process(lclk)
begin
if (lclk'event and lclk='1') then
-- Synchronous reset
if (lreset_n = '0') then
LPC_State <= IDLE;
W_Data(7 downto 0) <= "00000000"; -- init. both displays to all on
else
case LPC_State is
-- Looking for a START condition
when IDLE =>
if (lframe_nreg = '0') and (lad_rin = "0000") then
LPC_State <= START; -- START condition detected
end if;
-- Skip extra cycles on START frame
-- (can be many clock cycles)
-- and then, check for I/O write transaction
when START =>
if (lframe_nreg = '0') then -- frame still asserted
if (lad_rin /= "0000") then
LPC_State <= IDLE; -- unsupported start code
end if;
else
if (lad_rin(3 downto 1) = "001") then
LPC_State <= WADDN3; -- I/O write detected
else
LPC_State <= IDLE;
-- unsupported command
end if;
end if;
-- --------------------------------
-- I/O write transaction processing
-- --------------------------------
when WADDN3 => -- Write Data Address Nibble 3
-- Find next state
if (lframe_nreg = '0') or (lad_rin /= "0000") then
LPC_State <= IDLE; - -- abort cycle, bad frame
-- or address mismatch
else
LPC_State <= WADDN2;
end if;
when WADDN2 => -- Write Data Address Nibble 2
-- Find next state
if (lframe_nreg = '0') or (lad_rin /= "0000") then
LPC_State <= IDLE; -- abort cycle, bad frame
-- or address mismatch
else
LPC_State <= WADDN1;
end if;
when WADDN1 => -- Write Data Address Nibble 1
-- Find next state
if (lframe_nreg = '0') or (lad_rin /= "1000") then
LPC_State <= IDLE; -- abort cycle, bad frame
-- or address mismatch
else
LPC_State <= WADDN0;
end if;
when WADDN0 => -- Write Data Address Nibble 0
-- Find next state
if (lframe_nreg = '0') or (lad_rin /= "0000") then
PICMG ® COM Express ® Carrier Board Design Guide Rev. 2.0 / December 6, 2013
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