modules/*/wb_acq_core/acq_trigger.vhd: fix trigger alignment to last atom

We were asserting the trigger aligned with the first atom of the sample. This is wrong as the trigger belong to the last atom of the PRE TRIGGE state. Thus, it belongs to the last atom of the sample.

modules/*/wb_acq_core/acq_trigger.vhd: fix trigger alignment to last atom
We were asserting the trigger aligned with the first atom of the sample. This is wrong as the trigger belong to the last atom of the PRE TRIGGE state. Thus, it belongs to the last atom of the sample.
8ffd6150 · Lucas Russo · 5afbdb33 · 8ffd6150
Commit 8ffd6150 authored Jan 13, 2016 by Lucas Russo
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Showing with 12 additions and 5 deletions

acq_trigger.vhd hdl/modules/dbe_wishbone/wb_acq_core/acq_trigger.vhd +12 -5

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--- a/hdl/modules/dbe_wishbone/wb_acq_core/acq_trigger.vhd
+++ b/hdl/modules/dbe_wishbone/wb_acq_core/acq_trigger.vhd
@@ -388,7 +388,10 @@ begin
    end if;
  end process;

-  -- Hold trigger signal until a we are aligned and a valid sample is found
+  -- Hold trigger signal until a we are aligned and a valid sample is found.
+  -- The aligned term here refers to the last atom of a channel sample
+  -- (composed of atoms). For instance, if the channel is composed of 4 atoms,
+  -- the last channel atom would be number 3.
  p_trig_align : process (fs_clk_i)
  begin
    if rising_edge(fs_clk_i) then
@@ -404,10 +407,14 @@ begin
        end if;

        -- Wait until we have transfered the correct (aligned) number of samples
-        -- to output trigger
-        if trig_unaligned = '1' and acq_trig_align_cnt = acq_trig_align_cnt_max and
-            acq_valid_sel_out = '1' then -- will increment
-          trig_align <= '1';
+        -- to output trigger.
+        --
+        -- By design acq_trig_align_cnt_max would be at least 1, meaning a channel
+        -- composed of 2 atoms. So the arithmetic acq_trig_align_cnt_max-1 yields
+        -- valid values in all cases.
+        if trig_unaligned = '1' and acq_trig_align_cnt = acq_trig_align_cnt_max-1 and
+            acq_valid_sel_out = '1' then -- will increment to the last atom
+          trig_align <= '1'; -- Output trigger aligned with the last atom
        elsif acq_valid_sel_out = '1' then
          trig_align <= '0';
        end if;