Z80: Rd/Wr Mem/IO breakpoint/watchpoint sampled in middle of T3

Change-Id: I9dcca58f121da9e443bd18da8f13a099cfbc2056

src/Z80CpuMon.vhd

@@ -110,10 +110,8 @@ type state_type is (idle, nop_t1, nop_t2, nop_t3, nop_t4, rd_t1, rd_wa, rd_t2, r
     signal RFSH_n_int     : std_logic;
     signal M1_n_int       : std_logic;
     signal BUSAK_n_int    : std_logic;
-    signal BUSAK_n_comb   : std_logic;
     signal WAIT_n_latched : std_logic;
     signal TState         : std_logic_vector(2 downto 0);
-    signal TState1        : std_logic_vector(2 downto 0);
     signal SS_Single      : std_logic;
     signal SS_Step        : std_logic;
     signal SS_Step_held   : std_logic;
@@ -153,23 +151,17 @@ type state_type is (idle, nop_t1, nop_t2, nop_t3, nop_t4, rd_t1, rd_wa, rd_t2, r
     signal INT_n_sync     : std_logic;
     signal NMI_n_sync     : std_logic;
 
-    signal Rdy            : std_logic;
     signal Read_n         : std_logic;
     signal Read_n0        : std_logic;
-    signal Read_n1        : std_logic;
     signal Write_n        : std_logic;
     signal Write_n0       : std_logic;
     signal ReadIO_n       : std_logic;
     signal ReadIO_n0      : std_logic;
-    signal ReadIO_n1      : std_logic;
     signal WriteIO_n      : std_logic;
     signal WriteIO_n0     : std_logic;
     signal Sync           : std_logic;
     signal Sync0          : std_logic;
     signal Sync1          : std_logic;
-    signal Mem_IO_n       : std_logic;
-
-    signal MemState       : std_logic_vector(2 downto 0);
 
     signal Din            : std_logic_vector(7 downto 0);
     signal Dout           : std_logic_vector(7 downto 0);
@@ -327,40 +319,32 @@ begin
     -- really care about the data (it's re-read from memory by the disassembler).
     Sync0    <= '1' when WAIT_n = '1' and M1_n_int = '0' and TState = "010" and skipNextOpcode = '0' else '0';
 
-    -- For memory reads/write breakpoints we make the monitoring decision in the middle of T2
-    -- but only if WAIT_n is '1' so we catch the right data.
-    Read_n0    <= not (WAIT_n and (not RD_n_int) and (not MREQ_n_int) and (M1_n_int)) when TState = "010" else '1';
-    Write_n0   <= not (WAIT_n and (    RD_n_int) and (not MREQ_n_int) and (M1_n_int)) when TState = "010" else '1';
-
-    -- For IO reads/writes we make the monitoring decision in the middle of the second T2 cycle
-    -- but only if WAIT_n is '1' so we catch the right data.
-    -- This one cycle delay accounts for the forced wait state
-    ReadIO_n0  <= not (WAIT_n and (not RD_n_int) and (not IORQ_n_int) and (M1_n_int)) when TState1 = "010" else '1';
-    WriteIO_n0 <= not (WAIT_n and (    RD_n_int) and (not IORQ_n_int) and (M1_n_int)) when TState1 = "010" else '1';
+    -- For reads/write breakpoints we make the monitoring decision in the middle of T3
+    Read_n0    <= not ((not RD_n_int) and (not MREQ_n_int) and (M1_n_int)) when TState = "011" else '1';
+    Write_n0   <= not ((    RD_n_int) and (not MREQ_n_int) and (M1_n_int)) when TState = "011" else '1';
+    ReadIO_n0  <= not ((not RD_n_int) and (not IORQ_n_int) and (M1_n_int)) when TState = "011" else '1';
+    WriteIO_n0 <= not ((    RD_n_int) and (not IORQ_n_int) and (M1_n_int)) when TState = "011" else '1';
 
     -- Hold the monitoring decision so it is valid on the rising edge of the clock
-    -- For instruction fetches and writes, the monitor sees these at the start of T3
-    -- For reads, the data can arrive in the middle of T3 so delay until end of T3
+    -- For instruction fetches the monitor sees these at the end of T2
+    -- For reads and writes, the data is sampled in the middle of T3 so delay until end of T3
     watch_gen : process(CLK_n)
     begin
         if falling_edge(CLK_n) then
             Sync        <= Sync0;
-            Read_n1     <= Read_n0;
-            Read_n      <= Read_n1;
+            Read_n      <= Read_n0;
             Write_n     <= Write_n0;
-            ReadIO_n1   <= ReadIO_n0;
-            ReadIO_n    <= ReadIO_n1;
+            ReadIO_n    <= ReadIO_n0;
             WriteIO_n   <= WriteIO_n0;
             -- Latch wait seen by T80 on the falling edge, for use on the next rising edge
             WAIT_n_latched <= WAIT_n;
         end if;
     end process;
 
-    -- Register the exec data on the rising at the end of T2
+    -- Register the exec data on the rising edge of the clock at the end of T2
     ex_data_latch : process(CLK_n)
     begin
         if rising_edge(CLK_n) then
-            TState1 <= TState;
             if Sync = '1' then
                 ex_data <= Data;
             end if;
@@ -371,14 +355,14 @@ begin
     rd_data_latch : process(CLK_n)
     begin
         if falling_edge(CLK_n) then
-            if Read_n1 = '0' or ReadIO_n1 = '0' then
+            if Read_n0 = '0' or ReadIO_n0 = '0' then
                 rd_data <= Data;
             end if;
             memory_din <= Data;
         end if;
     end process;
 
-    -- Register the write data on the falling edge in the middle of T2
+    -- Register the read data on the falling edge of clock in the middle of T3
     wr_data_latch : process(CLK_n)
     begin
         if falling_edge(CLK_n) then