eb2: pop FIFOs only when both ready

hdl/eb_slave_core/eb_fifo.vhd

@@ -28,7 +28,7 @@ use work.wishbone_pkg.all;
 use work.eb_internals_pkg.all;
 use work.genram_pkg.all;
 
--- r_dat_o is valid when r_empty_o=0
+-- r_dat_o is valid when r_empty_o=0 (show ahead)
 -- w_dat_i is valid when w_push_i =1
 -- r_pop_i  affects r_empty_o on the next cycle
 -- w_push_i affects w_full_o  on the next cycle

hdl/eb_slave_core/eb_tx_mux.vhd

@@ -60,7 +60,7 @@ architecture rtl of eb_tx_mux is
   signal r_tx_stb    : std_logic;
   signal s_can_tx    : std_logic;
   signal s_dat_mux   : t_wishbone_data;
-  signal s_empty_mux : std_logic;
+  signal s_tag_mux   : std_logic;
   signal s_pass_mux  : std_logic;
   signal s_cfg_mux   : std_logic;
   signal s_wbm_mux   : std_logic;
@@ -83,7 +83,7 @@ begin
       tx_dat_o <= (others => '0');
     elsif rising_edge(clk_i) then
       if s_can_tx = '1' then -- is prior operation complete?
-        r_tx_stb <= not s_empty_mux and r_tag_valid;
+        r_tx_stb <= not s_tag_mux and r_tag_valid;
         tx_dat_o <= s_dat_mux;
         -- Control the TX cycle line
         if r_tag_valid = '1' then
@@ -108,40 +108,40 @@ begin
     (others => '-') when others; -- c_tag_drop_tx
   
   with r_tag_value select
-  s_empty_mux <=
-    pass_empty_i    when c_tag_pass_tx,
-    pass_empty_i    when c_tag_pass_on,
-    cfg_empty_i     when c_tag_cfg_req,
-    cfg_empty_i     when c_tag_cfg_ign,
-    wbm_empty_i     when c_tag_wbm_req,
-    wbm_empty_i     when c_tag_wbm_ign,
-    '0'             when others; -- c_tag_drop_tx
+  s_tag_mux <=
+    pass_empty_i                  when c_tag_pass_tx,
+    pass_empty_i                  when c_tag_pass_on,
+    cfg_empty_i                   when c_tag_cfg_req,
+    (pass_empty_i or cfg_empty_i) when c_tag_cfg_ign,
+    wbm_empty_i                   when c_tag_wbm_req,
+    (pass_empty_i or wbm_empty_i) when c_tag_wbm_ign,
+    '0'                           when others; -- c_tag_drop_tx
   
   with r_tag_value select
   s_pass_mux <=
-    '1'             when c_tag_pass_tx,
-    '1'             when c_tag_pass_on,
-    '1'             when c_tag_cfg_ign,
-    '1'             when c_tag_wbm_ign,
-    '0'             when others; -- c_tag_drop_tx, c_tag_cfg_req, c_tag_wbm_req
+    pass_empty_i                  when c_tag_pass_tx,
+    pass_empty_i                  when c_tag_pass_on,
+    (pass_empty_i or cfg_empty_i) when c_tag_cfg_ign,
+    (pass_empty_i or wbm_empty_i) when c_tag_wbm_ign,
+    '1'                           when others; -- c_tag_drop_tx, c_tag_cfg_req, c_tag_wbm_req
   
   with r_tag_value select
   s_cfg_mux <=
-    '1'              when c_tag_cfg_req,
-    '1'              when c_tag_cfg_ign,
-    '0'              when others;
+    cfg_empty_i                   when c_tag_cfg_req,
+    (pass_empty_i or cfg_empty_i) when c_tag_cfg_ign,
+    '1'                           when others;
   
   with r_tag_value select
   s_wbm_mux <=
-    '1'              when c_tag_wbm_req,
-    '1'              when c_tag_wbm_ign,
-    '0'              when others;
+    wbm_empty_i                   when c_tag_wbm_req,
+    (pass_empty_i or wbm_empty_i) when c_tag_wbm_ign,
+    '1'                           when others;
   
   -- Pop the queue we fed into TX
-  pass_pop_o <= s_can_tx and r_tag_valid and not pass_empty_i and s_pass_mux;
-  cfg_pop_o  <= s_can_tx and r_tag_valid and not cfg_empty_i  and s_cfg_mux;
-  wbm_pop_o  <= s_can_tx and r_tag_valid and not wbm_empty_i  and s_wbm_mux;
-  s_tag_pop  <= s_can_tx and r_tag_valid and not s_empty_mux;
+  pass_pop_o <= s_can_tx and r_tag_valid and not s_pass_mux;
+  cfg_pop_o  <= s_can_tx and r_tag_valid and not s_cfg_mux;
+  wbm_pop_o  <= s_can_tx and r_tag_valid and not s_wbm_mux;
+  s_tag_pop  <= s_can_tx and r_tag_valid and not s_tag_mux;
   
   -- Pop the tag FIFO if the register is empty/emptied
   tag_pop_o <= not tag_empty_i and (s_tag_pop or not r_tag_valid);