arty a7: Rework status LED colours

This frees up LEDs 4 and 5 by combining their status functions into
LED 0, which is now black when the system is in reset and yellow when
the system clock is not locked.  On configuations without litedram,
LED 0 now shows green rather than magenta.

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

fpga/top-arty.vhdl

@@ -156,6 +156,8 @@ architecture behaviour of toplevel is
     -- Status
     signal run_out : std_ulogic;
     signal run_outs : std_ulogic_vector(CPUS-1 downto 0);
+    signal init_done : std_ulogic;
+    signal init_err  : std_ulogic;
 
     -- Reset signals:
     signal soc_rst : std_ulogic;
@@ -204,9 +206,9 @@ architecture behaviour of toplevel is
     signal wb_sddma_stb_sent   : std_ulogic;
 
     -- Status LED
-    signal led_b_pwm : std_ulogic_vector(3 downto 0);
-    signal led_r_pwm : std_ulogic_vector(3 downto 0);
-    signal led_g_pwm : std_ulogic_vector(3 downto 0);
+    signal led_b_pwm : std_ulogic_vector(3 downto 0) := (others => '0');
+    signal led_r_pwm : std_ulogic_vector(3 downto 0) := (others => '0');
+    signal led_g_pwm : std_ulogic_vector(3 downto 0) := (others => '0');
 
     -- Dumb PWM for the LEDs, those RGB LEDs are too bright otherwise
     signal pwm_counter  : std_ulogic_vector(8 downto 0);
@@ -401,9 +403,8 @@ begin
                 pll_locked_out => system_clk_locked
                 );
 
-        led_b_pwm <= "1111";
-        led_r_pwm <= "1111";
-        led_g_pwm <= "0000";
+        init_done <= '1';
+        init_err  <= '0';
 
         -- Vivado barfs on those differential signals if left
         -- unconnected. So instanciate a diff. buffer and feed
@@ -501,9 +502,8 @@ begin
                 ddram_reset_n   => ddram_reset_n
                 );
 
-        led_b_pwm(0) <= not dram_init_done;
-        led_r_pwm(0) <= dram_init_error;
-        led_g_pwm(0) <= dram_init_done and not dram_init_error;
+        init_done <= dram_init_done;
+        init_err  <= dram_init_error;
 
     end generate;
 
@@ -802,6 +802,21 @@ begin
                      wb_sdcard2_out when wb_ext_is_sdcard = '1' and wb_ext_io_in.adr(13) = '1' else
                      wb_dram_ctrl_out;
 
+    status_led_colour : process(all)
+        variable rgb : std_ulogic_vector(2 downto 0);
+    begin
+        if soc_rst = '1' then
+            rgb := "000";
+        elsif system_clk_locked = '0' then
+            rgb := "110";
+        else
+            rgb := init_err & (init_done and not init_err) & (not init_done);
+        end if;
+        led_r_pwm(0) <= rgb(2);
+        led_g_pwm(0) <= rgb(1);
+        led_b_pwm(0) <= rgb(0);
+    end process;
+
     leds_pwm : process(system_clk)
     begin
         if rising_edge(system_clk) then
@@ -818,8 +833,8 @@ begin
         end if;
     end process;
 
-    led4 <= system_clk_locked;
-    led5 <= not soc_rst;
+    led4 <= '0';
+    led5 <= '0';
     led6 <= run_outs(1) when CPUS > 1 else '0';
     led7 <= run_outs(0);