--****************************************************************************************************
-- Programm Status Registers for ARM core
-- Designed by Ruslan Lepetenok
-- Modified 23.01.2003
--****************************************************************************************************

library	IEEE;
use IEEE.std_logic_1164.all;

use WORK.ARMPackage.all;

entity PSR is port(
						-- Global control signals
	                    nRESET    : in  std_logic;
						CLK       : in  std_logic;
						CLKEN     : in  std_logic;
						-- ALU Data in
						DataIn    : in  std_logic_vector(31 downto 0);
						PSRDInSel : in  std_logic;
						-- Current program state
						CPSRIn    : in  std_logic_vector(31 downto 0); 
						CPSRWrEn  : in  std_logic_vector(31 downto 0);
						CPSROut   : out std_logic_vector(31 downto 0); 
						CFlForMul : in  std_logic;
						-- Saved program state
						SPSRIn    : in  std_logic_vector(31 downto 0);
	                    SPSROut   : out std_logic_vector(31 downto 0);
						SPSRWrMsk : in  std_logic_vector(3 downto 0);
						-- PSR mode control
						PSRMode   : in  std_logic_vector(4 downto 0) 
						);
end PSR;

architecture RTL of PSR is

signal CPSR       : std_logic_vector(31 downto 0) := (others => '0');
signal SPSR_FIQ   : std_logic_vector(CPSR'range) := (others => '0');
signal SPSR_SVC   : std_logic_vector(CPSR'range) := (others => '0');
signal SPSR_Abort : std_logic_vector(CPSR'range) := (others => '0');
signal SPSR_IRQ   : std_logic_vector(CPSR'range) := (others => '0');
signal SPSR_Undef : std_logic_vector(CPSR'range) := (others => '0');
signal SPSRWrEn   : std_logic_vector(CPSR'range) := (others => '0');
signal SPSROutMUX : std_logic_vector(CPSR'range) := (others => '0');


-- Modes 
signal UserMode  : std_logic := '0'; 
signal FIQMode   : std_logic := '0'; 
signal IRQMode   : std_logic := '0'; 
signal SVCMode   : std_logic := '0'; 
signal AbortMode : std_logic := '0'; 
signal UndefMode : std_logic := '0'; 

signal CPSRRegIn  : std_logic_vector(CPSR'range) := (others => '0');
signal SPSRRegIn  : std_logic_vector(CPSR'range) := (others => '0');

-- Long multiplication(accumulation support)
signal CFlForLMul : std_logic := '0'; 

begin

-- Mode decode logic
UserMode <= '1' when PSRMode=CUserMode or PSRMode=CSystemMode else '0'; 
FIQMode  <= '1' when PSRMode=CFIQMode else '0';  
IRQMode  <= '1' when PSRMode=CIRQMode else '0';  
SVCMode  <= '1' when PSRMode=CSVCMode else '0';  
AbortMode <= '1' when PSRMode=CAbortMode else '0'; 
UndefMode <= '1' when PSRMode=CUndefMode else '0'; 		

-- Masks for write into SPSR	
SPSRWriteEnable:for i in SPSRWrMsk'range generate	
SPSRWrEn(i*8+7 downto i*8) <= (others => SPSRWrMsk(i));	
end generate; 	

-- CPSR/SPSR input multiplexer
CPSRRegIn <= DataIn when PSRDInSel='1' else CPSRIn;
SPSRRegIn <= DataIn when PSRDInSel='1' else SPSRIn;

-- Current program status
CurrentPSR:process(nRESET,CLK)
begin
if nRESET='0' then                       -- Reset
 CPSR <= CPSRInitVal;	
elsif CLK='1' and CLK'event then         -- Clock
 for i in CPSR'range loop
  if CPSRWrEn(i)='1' and CLKEN='1' then  -- Clock enable
   CPSR(i) <= CPSRRegIn(i); 
  end if;		
  end loop;
end if;	
end process;

-- Saved program statuses
FIQ_PSR:process(nRESET,CLK)
begin
if nRESET='0' then                                         -- Reset
 SPSR_FIQ <= (others => '0');	
elsif CLK='1' and CLK'event then                           -- Clock
 for i in SPSR_FIQ'range loop
  if FIQMode = '1' and SPSRWrEn(i)='1' and CLKEN='1' then  -- Clock enable
   SPSR_FIQ(i) <= SPSRRegIn(i); 
  end if;		
 end loop;
end if;	
end process;

IRQ_PSR:process(nRESET,CLK)
begin
if nRESET='0' then                                         -- Reset
 SPSR_IRQ <= (others => '0');	
elsif CLK='1' and CLK'event then                           -- Clock
 for i in SPSR_IRQ'range loop
  if IRQMode = '1' and SPSRWrEn(i)='1' and CLKEN='1' then  -- Clock enable
   SPSR_IRQ(i) <= SPSRRegIn(i); 
  end if;		
 end loop;
end if;	
end process;

SVC_PSR:process(nRESET,CLK)
begin
if nRESET='0' then                                         -- Reset
 SPSR_SVC <= (others => '0');	
elsif CLK='1' and CLK'event then                           -- Clock
 for i in SPSR_SVC'range loop
  if SVCMode = '1' and SPSRWrEn(i)='1' and CLKEN='1' then  -- Clock enable
   SPSR_SVC(i) <= SPSRRegIn(i); 
  end if;		
 end loop;
end if;	
end process;

Abort_PSR:process(nRESET,CLK)
begin
if nRESET='0' then                                           -- Reset
 SPSR_Abort <= (others => '0');	
elsif CLK='1' and CLK'event then                             -- Clock
 for i in SPSR_Abort'range loop
  if AbortMode = '1' and SPSRWrEn(i)='1' and CLKEN='1' then  -- Clock enable
   SPSR_Abort(i) <= SPSRRegIn(i); 
  end if;		
 end loop;
end if;	
end process;

Undef_PSR:process(nRESET,CLK)
begin
if nRESET='0' then                                           -- Reset
 SPSR_Undef <= (others => '0');	
elsif CLK='1' and CLK'event then                             -- Clock
 for i in SPSR_Undef'range loop
  if UndefMode = '1' and SPSRWrEn(i)='1' and CLKEN='1' then  -- Clock enable
   SPSR_Undef(i) <= SPSRRegIn(i); 
  end if;		
 end loop;
end if;	
end process;

-- Output multiplexers
SPSROutMUX <=  SPSR_FIQ   when CPSR(4 downto 0) = CFIQMode else  
	           SPSR_IRQ   when CPSR(4 downto 0) = CIRQMode else  
               SPSR_SVC   when CPSR(4 downto 0) = CSVCMode else  
               SPSR_Abort when CPSR(4 downto 0) = CAbortMode else  
	           SPSR_Undef when CPSR(4 downto 0) = CUndefMode else  
			   (others => CDnCr);

SPSROut <= SPSROutMUX;
           
CPSROut <= CPSR(CPSR'high downto 30)&CFlForLMul&CPSR(28 downto 0) when CFlForMul='1' -- Long multiplication
           else CPSR;	

CarryForLongMul:process(nRESET,CLK)
begin
if nRESET='0' then                -- Reset
 CFlForLMul <= '0'; 
elsif CLK='1' and CLK'event then  -- Clock
 if CLKEN='1' then                -- Clock enable
   CFlForLMul <= CPSRIn(29);
 end if;		
end if;	
end process;		

end RTL;