BSRAM progmem. fix Makefile memory command that does not work. add interrupts, bank 1, timer0. Timer0 not tested.

1 files changed, 27 insertions, 5 deletions

diff --git a/hdl/state_machine.vhd b/hdl/state_machine.vhd
index 5b1c623..1fb5291 100644
--- a/hdl/state_machine.vhd
+++ b/hdl/state_machine.vhd
@@ -31,7 +31,11 @@ entity state_machine is
     stack_dout : in  std_logic_vector(12 downto 0);
 
     alu_skip   : in std_logic;
-    alu_result : in std_logic_vector(7 downto 0)
+    alu_result : in std_logic_vector(7 downto 0);
+
+    irq_pending : in  std_logic;
+    gie_clear   : out std_logic := '0';
+    gie_set     : out std_logic := '0'
   );
 
 
@@ -67,6 +71,8 @@ begin
       instr_ret  <= '0';
       stack_push <= '0';
       stack_pop  <= '0';
+      gie_clear  <= '0';
+      gie_set    <= '0';
 
       if reset = '1' then
         pc_internal    <= (others => '0');
@@ -78,16 +84,30 @@ begin
         case state is
           when IFetch =>
 
+            -- Hardware interrupt: push PC, jump to vector, clear GIE
+            if irq_pending = '1' and not do_phantom_nop then
+              stack_din    <= pc_internal;
+              stack_push   <= '1';
+              pc_internal  <= "0000000000100";  -- 0x0004
+              gie_clear    <= '1';
+              instr          := instruction_decode((others => '0'));
+              is_phantom     := true;
+              is_skip_phantom := false;
+              do_phantom_nop := false;
+              state <= MRead;
+
             -- if we had a branch before, this cycle is a NOP.
-            if do_phantom_nop then
+            elsif do_phantom_nop then
               instr          := instruction_decode((others => '0'));
               do_phantom_nop := false;
               is_phantom     := true;
               -- is_skip_phantom carries over from whoever set do_phantom_nop
+              state <= MRead;
             else
               instr          := instruction_decode(opcode);
               is_phantom     := false;
               is_skip_phantom := false;
+              state <= MRead;
             end if;
 
             -- set use_literal based on decoded instruction, holds through MWrite
@@ -106,7 +126,6 @@ begin
             -- for bit-select operations
             bit_select <= instr.b;
 
-            state <= Mread;
 
           when MRead =>
 
@@ -145,13 +164,16 @@ begin
                 do_phantom_nop := true;
                 is_skip_phantom := false;
 
-              elsif instr.op = RETUR or instr.op = RETLW then
+              elsif instr.op = RETUR or instr.op = RETLW or instr.op = RETFIE then
 
                 -- pop the PC from stack.
                 pc_internal    <= stack_dout;
-                stack_pop      <= '1';     -- pop deferred to next cycle.
+                stack_pop      <= '1';
                 do_phantom_nop := true;
                 is_skip_phantom := false;
+                if instr.op = RETFIE then
+                  gie_set <= '1';
+                end if;
 
               else
                 pc_internal <= std_logic_vector(unsigned(pc_internal) + 1);