-- $HDR$--
--+++++++++--
--Source Archived--
--Version in Repository:--
-- $Log:  25083: Balloon_samosa.vhd 
--
--   Rev 1.2    3/13/2008 8:09:36 PM  David
-- First draft (Compiles) of SAMOSA interface
--
--+++++++++--
----------------------------------------------------------------------------------
-- Company: iTechnic Ltd
-- Engineer: D L Bisset
-- 
-- Create Date:    14:56:23 07/04/2006 
-- Design Name: 
-- Module Name:    Balloon_samosa - Behavioral 
-- Project Name: 
-- Target Devices: 
-- Tool versions: 
-- Description: Provides an Interface to the SAMOSA Connector on Balloon 3
--
-- Dependencies: 
--
-- Revision: 
-- Revision 0.01 - File Created
-- Additional Comments: 0v01 skeleton version, some logic analyser feed throughs to connector.
--
----------------------------------------------------------------------------------
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

---- Uncomment the following library declaration if instantiating
---- any Xilinx primitives in this code.
--library UNISIM;
--use UNISIM.VComponents.all;

entity Balloon_samosa is
	port (
			data_bus_in : in std_logic_vector (15 downto 0);
			data_bus_out : out std_logic_vector (15 downto 0);
			reg_add : in std_logic_vector (2 downto 0); --a23..a21 selects SAMOSA control Latches
			cpu_nwe : in std_logic;
			cpu_noe : in std_logic;
			samosa_select : in std_logic;
			park_IO : in std_logic;
			nreset : in std_logic;
			samosa_reset_in : in std_logic;
			irq_out : out std_logic;
			samosa_irq : in std_logic;
			samosa_absent: in std_logic;
			samosa_nre : out std_logic;
			samosa_nwe : out std_logic;
			samosa_cle : out std_logic;
			samosa_ale : out std_logic;
			samosa_nce : out std_logic;
			samosa_nwp : out std_logic;
			samosa_reset_out : out std_logic;
			samosa_skt_data : inout std_logic_vector(15 downto 0)
			);
end Balloon_samosa;

architecture Behavioral of Balloon_samosa is

constant ADDRESS_PORT : std_logic_vector(2 downto 0):= "000";
constant DATA_PORT    : std_logic_vector(2 downto 0):= "001";
constant STATUS_PORT  : std_logic_vector(2 downto 0):= "111";

signal address_port_select : std_logic;
signal data_port_select : std_logic;
signal samosa_active : std_logic;
signal samosa_external_active : std_logic;

signal nre_out : std_logic;
signal nwe_out : std_logic;
signal ale_out : std_logic;
signal nce_out : std_logic;
signal cle_out : std_logic;
signal nwp_out : std_logic;

signal samosa_status     : std_logic_vector (7 downto 0);
signal internal_data_out : std_logic_vector(15 downto 0);

begin
--SAMOSA Interface
--The address decodes correspond to writing an address, writing and reading data.
--It is assumed that the far end can keep up with Loon3 bus signal timings
--NOte that this may worsen EMC performance and latches might be needed to slow the bus.

samosa_reset_out <= nreset;

--Port selects
samosa_active <= '1' when (samosa_select = '1') and (park_IO = '0') else '0';
address_port_select <= '1' when (samosa_active = '1') and (reg_add = ADDRESS_PORT) else '0';
data_port_select    <= '1' when (samosa_active = '1') and (reg_add = DATA_PORT) else '0';
samosa_external_active <= '1' when (address_port_select = '1') or (data_port_select = '1') else '0';

--Create Socket IO signals
--This assumes we do not use the command port just the address and data ports.
nre_out <= '0' when (samosa_active = '1') and (cpu_noe = '0') else '1';
nwe_out <= '0' when (samosa_active = '1') and (cpu_nwe = '0') else '1';
ale_out <= '1' when (address_port_select = '1') else '0';
nce_out <= not samosa_external_active;
cle_out <= '0'; --We don't use the command write.
nwp_out <= '1'; --High enables writing will be shut down by park_IO.

--Park the IO bits to the SAMOSA bus
samosa_nre <= nre_out when (park_IO = '0') else '0';
samosa_nwe <= nwe_out when (park_IO = '0') else '0';
samosa_ale <= ale_out when (park_IO = '0') else '0';  
samosa_nce <= nce_out when (park_IO = '0') else '0';
samosa_cle <= cle_out when (park_IO = '0') else '0';
samosa_nwp <= nwp_out when (park_IO = '0') else '0';

--set the status word
samosa_status <= samosa_irq & "000000" & samosa_absent;

--Mux the internal data sources, note it is possible to add a SAMOSA bus version on reading from ADDRESS
with reg_add select
	internal_data_out <=
			samosa_skt_data when DATA_PORT,
			X"0000" when ADDRESS_PORT,
			X"00" & samosa_status when STATUS_PORT,
			X"0000" when others;

samosa_skt_data <= data_bus_in when (samosa_external_active = '1') and (nwe_out = '0') else "ZZZZZZZZZZZZZZZZ";

data_bus_out <= internal_data_out when (samosa_active = '1') else "ZZZZZZZZZZZZZZZZ"; 

end Behavioral;