From 9e61fd9456bb392db189045fb7368109e351b95b Mon Sep 17 00:00:00 2001
From: Paul Mathieu <paulmathieu@google.com>
Date: Sat, 6 Mar 2021 16:36:57 -0800
Subject: [PATCH] Add multi master sys bus

---
 sysbus/makefile         |  18 +++
 sysbus/sysbus.vhdl      | 197 ++++++++++++++++++++++++++++++++
 sysbus/sysbus_test.vhdl | 241 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 456 insertions(+)
 create mode 100644 sysbus/makefile
 create mode 100644 sysbus/sysbus.vhdl
 create mode 100644 sysbus/sysbus_test.vhdl

diff --git a/sysbus/makefile b/sysbus/makefile
new file mode 100644
index 0000000..b87aea6
--- /dev/null
+++ b/sysbus/makefile
@@ -0,0 +1,18 @@
+all: sim
+sim: test.ghw
+
+sim_sources = sysbus_test.vhdl
+sources = sysbus.vhdl
+test_entity = sysbus_test
+
+
+test.ghw: work-obj93.cf
+	ghdl -r $(test_entity) --wave=$@
+
+
+work-obj93.cf: $(sim_sources) $(sources)
+	ghdl -a $^
+
+PHONY: sim
+
+.PRECIOUS: test.ghw
diff --git a/sysbus/sysbus.vhdl b/sysbus/sysbus.vhdl
new file mode 100644
index 0000000..dfa2a64
--- /dev/null
+++ b/sysbus/sysbus.vhdl
@@ -0,0 +1,197 @@
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+
+entity sysbus is
+  port(
+        clk: in std_logic;
+        rst: in std_logic;
+
+  -- master port 0
+        m0_addr: in std_logic_vector(15 downto 0);
+        m0_wdata: in std_logic_vector(15 downto 0);
+        m0_rdata: out std_logic_vector(15 downto 0);
+        m0_re: in std_logic;
+        m0_we: in std_logic;
+        m0_busy: out std_logic;
+
+  -- master port 1
+        m1_addr: in std_logic_vector(15 downto 0);
+        m1_wdata: in std_logic_vector(15 downto 0);
+        m1_rdata: out std_logic_vector(15 downto 0);
+        m1_re: in std_logic;
+        m1_we: in std_logic;
+        m1_busy: out std_logic;
+
+  -- actual bus
+        bus_addr: out std_logic_vector(15 downto 0);
+        bus_wdata: out std_logic_vector(15 downto 0);
+        bus_rdata: in std_logic_vector(15 downto 0);
+        bus_re: out std_logic;
+        bus_we: out std_logic
+      );
+end entity sysbus;
+
+architecture behavior of sysbus is
+  type bus_state is (IDLE, READING, PENDING);
+
+  signal owner_next, owner: std_logic_vector(0 to 1);
+  signal state_next, state: bus_state;
+
+  signal pend_addr, pend_addr_next: std_logic_vector(15 downto 0);
+  signal pend_wdata, pend_wdata_next: std_logic_vector(15 downto 0);
+  signal pend, pend_next: std_logic_vector(0 to 1);
+
+  signal were: std_logic_vector(0 to 3);
+begin
+
+  were <= m0_we & m1_we & m0_re & m1_re;
+
+  process(were, m0_addr, m0_wdata, m1_addr, m1_wdata, bus_rdata, state, owner, pend, pend_addr, pend_wdata)
+  begin
+    if pend = "00" then
+      m0_busy <= '0';
+      m1_busy <= '0';
+    else
+      m0_busy <= '1';
+      m1_busy <= '1';
+    end if;
+
+    pend_next <= pend;
+    owner_next <= "00";
+
+    bus_we <= '0';
+    bus_re <= '0';
+
+    -- some defaults
+    bus_addr <= x"0000";
+    bus_wdata <= x"0000";
+
+    m0_rdata <= x"0000";
+    m1_rdata <= x"0000";
+
+    case state is
+      when READING =>
+        if owner = "10" then
+          m0_rdata <= bus_rdata;
+          m1_busy <= '1';
+        else
+          m1_rdata <= bus_rdata;
+          m0_busy <= '1';
+        end if;
+        if pend = "00" then
+          state_next <= IDLE;
+        else
+          state_next <= PENDING;
+        end if;
+
+      when PENDING =>
+        bus_addr <= pend_addr;
+        bus_we <= '1';
+        bus_wdata <= pend_wdata;
+        pend_next <= "00";
+        state_next <= IDLE;
+
+      when IDLE =>
+        case were is
+          when "0000" =>
+            -- chill
+          when "1000" =>
+            bus_addr <= m0_addr;
+            bus_wdata <= m0_wdata;
+            bus_we <= '1';
+            bus_re <= '0';
+          when "0100" =>
+            bus_addr <= m1_addr;
+            bus_wdata <= m1_wdata;
+            bus_we <= '1';
+            bus_re <= '0';
+          when "1100" =>
+            bus_addr <= m0_addr;
+            bus_wdata <= m0_wdata;
+            bus_we <= '1';
+            bus_re <= '0';
+
+            pend_next <= "01";
+            pend_addr_next <= m1_addr;
+            pend_wdata_next <= m1_wdata;
+            state_next <= PENDING;
+
+          when "0010" =>
+            state_next <= READING;
+            owner_next <= "10";
+
+            bus_addr <= m0_addr;
+            bus_we <= '0';
+            bus_re <= '1';
+
+          when "0001" =>
+            state_next <= READING;
+            owner_next <= "01";
+
+            bus_addr <= m1_addr;
+            bus_we <= '0';
+            bus_re <= '1';
+
+          when "0011" =>
+            state_next <= READING;
+            owner_next <= "10";
+
+            bus_addr <= m0_addr;
+            bus_we <= '0';
+            bus_re <= '1';
+
+            m1_busy <= '1';
+
+          when "1001" =>
+            state_next <= READING;
+            owner_next <= "01";
+
+            bus_addr <= m1_addr;
+            bus_we <= '0';
+            bus_re <= '1';
+
+            pend_next <= "10";
+            pend_addr_next <= m0_addr;
+            pend_wdata_next <= m0_wdata;
+
+            m0_busy <= '1';
+
+          when "0110" =>
+            state_next <= READING;
+            owner_next <= "10";
+
+            bus_addr <= m0_addr;
+            bus_we <= '0';
+            bus_re <= '1';
+
+            pend_next <= "01";
+            pend_addr_next <= m1_addr;
+            pend_wdata_next <= m1_wdata;
+
+            m1_busy <= '1';
+
+          when others =>
+            -- blarg
+        end case;
+    end case;
+  end process;
+
+  process(clk, rst)
+  begin
+    if rst = '1' then
+      state <= IDLE;
+      owner <= "00";
+      pend <= "00";
+      pend_addr <= x"0000";
+      pend_wdata <= x"0000";
+    elsif rising_edge(clk) then
+      state <= state_next;
+      owner <= owner_next;
+      pend <= pend_next;
+      pend_addr <= pend_addr_next;
+      pend_wdata <= pend_wdata_next;
+    end if;
+  end process;
+
+end behavior;
diff --git a/sysbus/sysbus_test.vhdl b/sysbus/sysbus_test.vhdl
new file mode 100644
index 0000000..31e7b8c
--- /dev/null
+++ b/sysbus/sysbus_test.vhdl
@@ -0,0 +1,241 @@
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+use std.textio.all;
+
+entity sysbus_test is
+end sysbus_test;
+
+architecture rtl of sysbus_test is
+
+  component sysbus is
+    port(
+          clk: in std_logic;
+          rst: in std_logic;
+
+        -- master port 0
+          m0_addr: in std_logic_vector(15 downto 0);
+          m0_wdata: in std_logic_vector(15 downto 0);
+          m0_rdata: out std_logic_vector(15 downto 0);
+          m0_re: in std_logic;
+          m0_we: in std_logic;
+          m0_busy: out std_logic;
+
+        -- master port 1
+          m1_addr: in std_logic_vector(15 downto 0);
+          m1_wdata: in std_logic_vector(15 downto 0);
+          m1_rdata: out std_logic_vector(15 downto 0);
+          m1_re: in std_logic;
+          m1_we: in std_logic;
+          m1_busy: out std_logic;
+
+        -- actual bus
+          bus_addr: out std_logic_vector(15 downto 0);
+          bus_wdata: out std_logic_vector(15 downto 0);
+          bus_rdata: in std_logic_vector(15 downto 0);
+          bus_re: out std_logic;
+          bus_we: out std_logic
+        );
+  end component;
+
+  signal finished: std_logic := '0';
+  signal clk, rst: std_logic := '0';
+
+  signal m0_addr, m0_wdata, m0_rdata: std_logic_vector(15 downto 0);
+  signal m0_re, m0_we, m0_busy: std_logic;
+  signal m1_addr, m1_wdata, m1_rdata: std_logic_vector(15 downto 0);
+  signal m1_re, m1_we, m1_busy: std_logic;
+  signal bus_addr, bus_wdata, bus_rdata: std_logic_vector(15 downto 0);
+  signal bus_re, bus_we : std_logic;
+
+  signal bus_rdata_next: std_logic_vector(15 downto 0);
+
+begin
+  dut: sysbus port map(clk => clk, rst => rst,
+                      m0_addr => m0_addr, m0_wdata => m0_wdata, m0_rdata => m0_rdata,
+                      m0_re => m0_re, m0_we => m0_we, m0_busy => m0_busy,
+                      m1_addr => m1_addr, m1_wdata => m1_wdata, m1_rdata => m1_rdata,
+                      m1_re => m1_re, m1_we => m1_we, m1_busy => m1_busy,
+                      bus_addr => bus_addr, bus_wdata => bus_wdata, bus_rdata => bus_rdata,
+                      bus_re => bus_re, bus_we => bus_we
+                  );
+
+  -- clock
+  process
+  begin
+    if finished = '0' then
+      clk <= not clk;
+      wait for 5 ns;
+    else
+      clk <= '0';
+      wait;
+    end if;
+  end process;
+
+  -- memory
+  process(bus_re, bus_addr)
+  begin
+    bus_rdata_next <= x"0000";
+    if bus_re = '1' then
+      case bus_addr is
+        when x"feed" =>
+          bus_rdata_next <= x"babe";
+        when x"dead" =>
+          bus_rdata_next <= x"beef";
+        when others =>
+      end case;
+    end if;
+  end process;
+
+  process(clk, rst)
+  begin
+    if rst = '1' then
+      bus_rdata <= x"0000";
+    elsif rising_edge(clk) then
+      bus_rdata <= bus_rdata_next;
+    end if;
+  end process;
+
+  process
+  begin
+    rst <= '1';
+
+    m0_re <= '0';
+    m0_we <= '0';
+    m1_re <= '0';
+    m1_we <= '0';
+
+    wait for 1 ns;
+    assert(m0_busy='0') report "Fail rst" severity error;
+    assert(m1_busy='0') report "Fail rst" severity error;
+
+    rst <= '0';
+
+    wait for 10 ns;
+    assert(m0_busy='0') report "Should still be idle" severity error;
+    assert(m1_busy='0') report "Should still be idle" severity error;
+
+    -- m0 write
+
+    m0_addr <= x"feed";
+    m0_wdata <= x"babe";
+    m0_we <= '1';
+
+    wait for 10 ns;
+    assert(bus_addr=x"feed") report "Did not do write" severity error;
+    assert(bus_wdata=x"babe") report "Did not do write" severity error;
+
+    m0_we <= '0';
+
+    -- read
+    m0_re <= '1';
+    wait for 10 ns;
+    assert(m0_rdata=x"babe") report "Did not do read" severity error;
+    assert(m1_busy='1') report "Did not do block m1 for m0 read" severity error;
+
+    m0_re <= '0';
+
+    wait for 10 ns;
+    assert(m0_busy='0') report "m0 was not idle" severity error;
+    assert(m1_busy='0') report "m1 was not idle" severity error;
+
+    -- m1 write
+
+    m1_addr <= x"dead";
+    m1_wdata <= x"beef";
+    m1_we <= '1';
+
+    wait for 10 ns;
+    assert(bus_addr=x"dead") report "Did not do write" severity error;
+    assert(bus_wdata=x"beef") report "Did not do write" severity error;
+
+    m1_we <= '0';
+
+    -- read
+    m1_re <= '1';
+    wait for 10 ns;
+    assert(m1_rdata=x"beef") report "Did not do read m1" severity error;
+    assert(m0_busy='1') report "Did not do block m0 for m1 read" severity error;
+
+    m1_re <= '0';
+
+    wait for 10 ns;
+    assert(m0_busy='0') report "m0 was not idle" severity error;
+    assert(m1_busy='0') report "m1 was not idle" severity error;
+
+
+    -- serious shit below
+    -- concurent writes
+
+    m0_addr <= x"feed";
+    m0_wdata <= x"babe";
+    m0_we <= '1';
+
+    m1_addr <= x"dead";
+    m1_wdata <= x"beef";
+    m1_we <= '1';
+
+    wait for 9 ns;
+    assert(bus_addr=x"feed") report "Did not do write m0" severity error;
+    assert(bus_wdata=x"babe") report "Did not do write m0" severity error;
+    wait for 1 ns;
+    assert(m1_busy='1') report "Did not do delay m1" severity error;
+
+    m0_we <= '0';
+    m1_we <= '0';
+
+    wait for 9 ns;
+    assert(bus_addr=x"dead") report "Did not do write m1" severity error;
+    assert(bus_wdata=x"beef") report "Did not do write m1" severity error;
+    wait for 1 ns;
+
+    wait for 10 ns;
+    assert(m0_busy='0') report "m0 was not idle" severity error;
+    assert(m1_busy='0') report "m1 was not idle" severity error;
+
+    -- concurrent reads (!!)
+
+    m0_re <= '1';
+    m1_re <= '1';
+    wait for 10 ns;
+    assert(m0_rdata=x"babe") report "Did not do read m0" severity error;
+    assert(m1_busy='1') report "Did not do block m1 for m0 read" severity error;
+
+    m0_re <= '0';
+
+    wait for 20 ns;
+    assert(m1_busy='0') report "m1 was not idle" severity error;
+    assert(m1_rdata=x"beef") report "Did not do read m1" severity error;
+    assert(m0_busy='1') report "Did not do block m0 for m1 read" severity error;
+
+    m1_re <= '0';
+
+    wait for 10 ns;
+    assert(m0_busy='0') report "m0 was not idle" severity error;
+    assert(m1_busy='0') report "m1 was not idle" severity error;
+
+    -- concurrent read & write (OMG)
+    m1_re <= '1';
+    m0_we <= '1';
+
+    wait for 10 ns;
+    assert(m1_rdata=x"beef") report "Did not do read m1" severity error;
+    assert(m0_busy='1') report "Did not do block m0 for m1 read" severity error;
+
+    m1_re <= '0';
+
+    wait for 10 ns;
+    assert(bus_addr=x"feed") report "Did not do write m0" severity error;
+    assert(bus_wdata=x"babe") report "Did not do write m0" severity error;
+
+    m0_we <= '0';
+
+    wait for 10 ns;
+    assert(m0_busy='0') report "m0 was not idle" severity error;
+    assert(m1_busy='0') report "m1 was not idle" severity error;
+
+    assert false report "Test done." severity note;
+    finished <= '1';
+    wait;
+  end process;
+end rtl;