soc: Implement a global timebase across all cores

Now all cores see the same timebase value at any given instant.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

common.vhdl

@@ -264,7 +264,6 @@ package common is
     type ctrl_t is record
         wait_state: std_ulogic;
         run: std_ulogic;
-	tb: std_ulogic_vector(63 downto 0);
 	dec: std_ulogic_vector(63 downto 0);
 	msr: std_ulogic_vector(63 downto 0);
         cfar: std_ulogic_vector(63 downto 0);

core.vhdl

@@ -31,6 +31,9 @@ entity core is
 	-- Alternate reset (0xffff0000) for use by DRAM init fw
 	alt_reset    : in std_ulogic;
 
+        -- Global timebase
+        timebase     : in std_ulogic_vector(63 downto 0);
+
 	-- Wishbone interface
         wishbone_insn_in  : in wishbone_slave_out;
         wishbone_insn_out : out wishbone_master_out;
@@ -373,6 +376,7 @@ begin
         port map (
             clk => clk,
             rst => rst_ex1,
+            timebase => timebase,
             flush_in => flush,
 	    busy_out => ex1_busy_out,
             e_in => decode2_to_execute1,

execute1.vhdl

@@ -34,6 +34,8 @@ entity execute1 is
 	ext_irq_in : std_ulogic;
         interrupt_in : WritebackToExecute1Type;
 
+        timebase : std_ulogic_vector(63 downto 0);
+
 	-- asynchronous
         l_out : out Execute1ToLoadstore1Type;
         fp_out : out Execute1ToFPUType;
@@ -1901,8 +1903,8 @@ begin
 
     -- Slow SPR read mux
     with ex1.spr_select.sel select spr_result <=
-        ctrl.tb when SPRSEL_TB,
+        timebase when SPRSEL_TB,
-        32x"0" & ctrl.tb(63 downto 32) when SPRSEL_TBU,
+        32x"0" & timebase(63 downto 32) when SPRSEL_TBU,
         ctrl.dec when SPRSEL_DEC,
         32x"0" & PVR_MICROWATT when SPRSEL_PVR,
         log_wr_addr & ex2.log_addr_spr when SPRSEL_LOGA,
@@ -1956,16 +1958,14 @@ begin
         end if;
 
 	ctrl_tmp <= ctrl;
-	-- FIXME: run at 512MHz not core freq
-	ctrl_tmp.tb <= std_ulogic_vector(unsigned(ctrl.tb) + 1);
 	ctrl_tmp.dec <= std_ulogic_vector(unsigned(ctrl.dec) - 1);
 
         x_to_pmu.mfspr <= '0';
         x_to_pmu.mtspr <= '0';
-        x_to_pmu.tbbits(3) <= ctrl.tb(63 - 47);
+        x_to_pmu.tbbits(3) <= timebase(63 - 47);
-        x_to_pmu.tbbits(2) <= ctrl.tb(63 - 51);
+        x_to_pmu.tbbits(2) <= timebase(63 - 51);
-        x_to_pmu.tbbits(1) <= ctrl.tb(63 - 55);
+        x_to_pmu.tbbits(1) <= timebase(63 - 55);
-        x_to_pmu.tbbits(0) <= ctrl.tb(63 - 63);
+        x_to_pmu.tbbits(0) <= timebase(63 - 63);
         x_to_pmu.pmm_msr <= ctrl.msr(MSR_PMM);
         x_to_pmu.pr_msr <= ctrl.msr(MSR_PR);
 

soc.vhdl

@@ -271,6 +271,8 @@ architecture behaviour of soc is
 
     signal core_run_out       : std_ulogic_vector(NCPUS-1 downto 0);
 
+    signal timebase : std_ulogic_vector(63 downto 0);
+
     function wishbone_widen_data(wb : wb_io_master_out) return wishbone_master_out is
         variable wwb : wishbone_master_out;
     begin
@@ -350,6 +352,21 @@ begin
         end if;
     end process;
 
+    -- Timebase just increments at the system clock frequency.
+    -- There is currently no way to set it.
+    -- Ideally it would (appear to) run at 512MHz like IBM POWER systems,
+    -- but Linux seems to cope OK with it being 100MHz or whatever.
+    tbase: process(system_clk)
+    begin
+        if rising_edge(system_clk) then
+            if soc_reset = '1' then
+                timebase <= (others => '0');
+            else
+                timebase <= std_ulogic_vector(unsigned(timebase) + 1);
+            end if;
+        end if;
+    end process;
+
     -- Processor cores
     processors: for i in 0 to NCPUS-1 generate
         core: entity work.core
@@ -374,6 +391,7 @@ begin
 	    rst => rst_core(i),
 	    alt_reset => alt_reset_d,
             run_out => core_run_out(i),
+            timebase => timebase,
 	    wishbone_insn_in => wb_masters_in(i + NCPUS),
 	    wishbone_insn_out => wb_masters_out(i + NCPUS),
 	    wishbone_data_in => wb_masters_in(i),