1. Data Stack Lecture 8.2 A VHDL Forth Core for FPGAs: Sect. 3

2. FC16 Forth Core

3. Data Stack

4. A 32 x 16 Stack

5. A 32 x 16 Stack Module

6. entity stack_ctrl is port ( clr: in STD_LOGIC; clk: in STD_LOGIC; push: in STD_LOGIC; pop: in STD_LOGIC; we: out STD_LOGIC; amsel: out STD_LOGIC; wr_addr: out STD_LOGIC_VECTOR (4 downto 0); rd_addr: out STD_LOGIC_VECTOR (4 downto 0); full: out STD_LOGIC; empty: out STD_LOGIC ); end stack_ctrl; 00000 11111 stack_ctrl32 rd_addr wr_addr

7. architecture stack_ctrl_arch of stack_ctrl is signal full_flag, empty_flag: STD_LOGIC; begin stk: process(clr, clk, push, pop, full_flag, empty_flag) variable push_addr, pop_addr: STD_LOGIC_VECTOR(4 downto 0); begin if clr = '1' then push_addr := "11111"; pop_addr := "00000"; empty_flag <= '1'; full_flag <= '0'; wr_addr <= "11111"; rd_addr <= "00000"; full <= full_flag; empty <= empty_flag; stack_ctrl32

8. elsif clk'event and clk = '1' then if push = '1' then if pop = ‘0' then if full_flag = '0' then push_addr := push_addr - 1; pop_addr := push_addr + 1; empty_flag <= '0'; if push_addr = "11111” then full_flag <= '1'; push_addr := "00000"; end if; else –- write to top of stack (pop_addr) without pushing -- don’t change push_addr and pop_addr end if; stack_ctrl32 00000 11111 rd_addr wr_addr

9. 00000 11111 rd_addr wr_addr stack_ctrl32 elsif pop = '1' then if empty_flag = '0' then pop_addr := pop_addr + 1; if full_flag = '0' then push_addr := push_addr + 1; end if; full_flag <= '0'; if pop_addr = "00000" then empty_flag <= '1'; end if; wr_addr <= push_addr; rd_addr <= pop_addr; end if;

10. 00000 11111 rd_addr wr_addr stack_ctrl full <= full_flag; empty <= empty_flag; if push = '1' and full_flag = '0' then we <= '1'; else we <= '0'; end if; if push = '1' and pop = ‘1' then amsel <= '1'; else amsel <= '0'; end if; end process stk; end stack_ctrl_arch;

11. A 32 x 16 Stack Module

12. Data Stack

13. WHYP Data Stack Instructions DUP( n -- n n ) SWAP( a b -- b a ) DROP( a -- ) OVER( a b -- a b a ) ROT( a b c -- b c a ) -ROT( a b c -- c a b ) NIP( a b -- b ) TUCK( a b -- b a b ) ROT_DROP( a b c -- b c ) ROT_DROP_SWAP ( a b c -- c b ) 2DUP( a b -- a b a b ) Note: 2DUP = OVER OVER

14. Hex OpcodeNameFunction 0000NOP No operation 0001DUP Duplicate T and push data stack. N <= T; N2 <= N; 0002SWAP Exchange T and N. T <= N; N <= T; 0003DROP Drop T and pop data stack. T <= N; N <= N2; 0004OVER Duplicate N into T and push data stack. T <= N; N <= T; N2 <= N; 0005ROT Rotate top 3 elements on stack clockwise. T <= N2; N <= T; N2 <= N; 0006-ROT Rotate top 3 elements on stack counter-clockwise. T <= N; N <= N2; N2 <= T; 0007NIP Drop N and pop rest of data stack. T is unchanged. N <= N2; 0008TUCK Duplicate T into N2 and push rest of data stack. N2 <= T; 0009ROT_DROP Drop N2 and pop rest of data stack. T and N are unchanged. Equivalent to ROT DROP 000AROT_DROP_SWAP Drop N2 and pop rest of data stack. T and N are exchanged. Equivalent to ROT DROP SWAP Data Stack Instructions

15. when dup => nload <= '1'; dpush <= '1'; Duplicate T and push data stack. N <= T; N2 <= N; DUP( n -- n n )

16. Exchange T and N. T <= N; N <= T; when swap => tload <= '1'; nload <= '1'; tsel <= "111"; SWAP ( a b -- b a )

17. Drop T and pop data stack. T <= N; N <= N2; when drop => tload <= '1'; nload <= '1'; tsel <= "111"; nsel <= "01"; dpop <= '1'; DROP( a -- )

18. Duplicate N into T and push data stack. T <= N; N <= T; N2 <= N; when over => tload <= '1'; nload <= '1'; tsel <= "111"; dpush <= '1'; OVER( a b -- a b a )

19. Rotate top 3 elements on stack clockwise. T <= N2; N <= T; N2 <= N; when rot => tload <= '1'; nload <= '1'; tsel <= "110"; dpush <= '1'; dpop <= '1'; ROT( a b c -- b c a )

20. Rotate top 3 elements on stack counter- clockwise. T <= N; N <= N2; N2 <= T; when mrot => tload <= '1'; nload <= '1'; tsel <= "111"; nsel <= "01"; ssel <= '1'; dpush <= '1'; dpop <= '1'; -ROT( a b c -- c a b )

21. Drop N and pop rest of data stack. T is unchanged. N <= N2; when nip => nload <= '1'; nsel <= "01"; dpop <= '1'; NIP( a b -- b )

22. Duplicate T into N2 and push rest of data stack. N2 <= T; when tuck => ssel <= '1'; dpush <= '1'; TUCK( a b -- b a b )

23. ROT_DROP( a b c -- b c ) Drop N2 and pop rest of data stack. T and N are unchanged. Equivalent to ROT DROP when rot_drop => dpop <= '1';

24. ROT_DROP_SWAP ( a b c -- c b ) Drop N2 and pop rest of data stack. T and N are exchanged. Equivalent to ROT DROP SWAP when rot_drop_swap => tload <= '1'; nload <= '1'; tsel <= "111"; dpop <= '1';