From f906a6e4a3f5af7f8187a6e33287253fd484e70b Mon Sep 17 00:00:00 2001
From: yannickreiss <yannick.reiss@protonmail.ch>
Date: Wed, 27 Sep 2023 20:44:03 +0200
Subject: [PATCH] Implement push and pop in branch

---
 fpga/src/bfpu.vhd   |  5 +++--
 fpga/src/branch.vhd | 53 ++++++++++++++++++++++++++++++++++++---------
 2 files changed, 46 insertions(+), 12 deletions(-)

diff --git a/fpga/src/bfpu.vhd b/fpga/src/bfpu.vhd
index 848bc00..ff6d86c 100644
--- a/fpga/src/bfpu.vhd
+++ b/fpga/src/bfpu.vhd
@@ -78,6 +78,7 @@ architecture arch of bfpu is
             cell_value  :   in  std_logic_vector(7 downto 0);
 
             skip        :   out std_logic;
+            jump        :   out std_logic;
 		    pc_enable	:	out	std_logic;
 		    pc_out	    :   out	std_logic_vector(7 downto 0)
         );
@@ -86,7 +87,6 @@ architecture arch of bfpu is
     signal s_clk            :   std_logic;
     signal s_instrAddr      :   std_logic_vector(7 downto 0);
     signal s_instruction    :   std_logic_vector(2 downto 0);
-    signal s_instrAddr_branch : std_logic_vector(7 downto 0);
 
     signal s_cell_out       :   std_logic_vector(7 downto 0);
     signal s_cell_in        :   std_logic_vector(7 downto 0);
@@ -162,8 +162,9 @@ begin
         instr_addr  => s_instrAddr,
         cell_value  => s_cell_out,
         skip        => s_skip,
+        jump        => s_jmp_pc,
         pc_enable   => s_enable_pc,
-        pc_out      => s_instrAddr_branch
+        pc_out      => s_jmp_addr_pc
     );
 
     s_enable_ptr    <= s_skip and s_enable_ptr_o;
diff --git a/fpga/src/branch.vhd b/fpga/src/branch.vhd
index e4e6dbc..cf7c1c7 100644
--- a/fpga/src/branch.vhd
+++ b/fpga/src/branch.vhd
@@ -16,6 +16,7 @@ entity branch is
 
         skip        :   out std_logic;
 		pc_enable	:	out	std_logic;
+        jump        :   out std_logic;
 		pc_out	    :   out	std_logic_vector(7 downto 0)
     );
 end branch;
@@ -26,10 +27,9 @@ architecture impl of branch is
 
     signal addr_stack       : stack := (others => (others => '0'));
     signal nested           : std_logic_vector(7 downto 0) := (others => '0'); -- count nested loops
-    signal jump_destination : std_logic_vector(7 downto 0);
     signal skip_internal    : std_logic := '0';
     signal stack_ptr        : std_logic_vector(7 downto 0) := (others => '0');
-    signal push_state       : std_logic;
+    signal push_state       : std_logic := '1';
 
 begin
 
@@ -42,7 +42,7 @@ begin
             end if;
         end if;
     end process;
-    
+
     -- Process p_continue: set skip to false
     p_continue : process (clk)
     begin
@@ -52,7 +52,7 @@ begin
             end if;
         end if;
     end process;
-    
+
     -- Process p_nest : raise nest by one as [ is passed
     p_nest : process (clk)
     begin
@@ -62,7 +62,7 @@ begin
             end if;
         end if;
     end process;
-    
+
     -- Process p_unnest : lower nest, as ] is passed
     p_unnest : process (clk)
     begin
@@ -72,19 +72,52 @@ begin
             end if;
         end if;
     end process;
-    
+
     -- Process p_push : raise stack and push address
     p_push : process (clk)
     begin
-        -- TODO: Implement
+        if rising_edge(clk) and instruction = "110" and unsigned(cell_value) > 0 and skip_internal = '0' then
+            if push_state = '0' then
+                -- restore push_state and push address
+                addr_stack(to_integer(unsigned(stack_ptr))) <= instr_addr;
+                push_state <= '1';
+                pc_enable <= '1';
+            else
+                -- raise stack, disable pc and unset push_state
+                stack_ptr <= std_logic_vector(unsigned(stack_ptr) + 1);
+                pc_enable <= '0';
+                push_state <= '0';
+            end if;
+        end if;
     end process;
-    
+
     -- Process p_pop : read address to jump address and lower stack
     p_pop : process (clk)
     begin
-        -- TODO: Implement
+        if rising_edge(clk) and instruction = "111" and unsigned(cell_value) > 0 and skip_internal = '0' then
+            if push_state = '1' then
+                -- set address to pc_out, disable pc and unset push_state
+                pc_out <= addr_stack(to_integer(unsigned(stack_ptr)));
+                pc_enable <= '0';
+                push_state <= '0';
+            else
+                -- set pc to enabled, restore push_state and lower stack
+                pc_enable <= '1';
+                push_state <= '1';
+                stack_ptr <= std_logic_vector(unsigned(stack_ptr) - 1);
+            end if;
+        end if;
+
+        -- regulate jump
+        if rising_edge(clk) then
+            if instruction = "111" and unsigned(cell_value) > 0 and skip_internal = '0' and push_state = '0' then
+                jump <= '1';
+            else
+                jump <= '0';
+            end if;
+        end if;
     end process;
-    
+
     skip <= skip_internal;
 
 end impl;