hw: Fix FREP stalling logic

To track if all instructions in the current loop nest have
been stored in the buffer we compare the write pointer to
the end pointer of the loop nest. However, this must only be
done when writing a loop nest instruction. Previously, we were
using `loop_active_q` to check this, but it is incorrect, as
`loop_active_q` tells us if we already started executing the loop.
Instead, `loop_cnt_q > 0` tells us if we have just received an FREP,
and thus should be counting the following instructions.

Author: colluca

hw/snitch_cluster/src/snitch_sequencer.sv

@@ -401,7 +401,9 @@ module snitch_sequencer import snitch_pkg::*; #(
   // is nested within the current loop nest. The latter means checking if the write
   // pointer is within the outermost loop bounds. But the write pointer can wrap to
   // the start of the loop, so we also need to track if we've already received all
-  // instructions.
+  // instructions. And this involves comparing the write pointer to the end pointer,
+  // when writing a loop nest instruction. The first instructions following an FREP,
+  // i.e. received while loop_cnt_q > 0, are guaranteed to be within the loop nest.
 
   logic rb_wptr_within_bounds;
   logic [DepthBits-1:0] nest_start_pointer, nest_end_pointer;
@@ -411,7 +413,7 @@ module snitch_sequencer import snitch_pkg::*; #(
     nest_start_pointer = nest_cfg_q[0].base_pointer;
     nest_end_pointer = nest_cfg_q[0].base_pointer + nest_cfg_q[0].max_inst;
 
-    if (loop_active_q && (rb_wptr == nest_end_pointer) && (core_rb_valid && core_rb_ready)) begin
+    if ((loop_cnt_q > 0) && (rb_wptr == nest_end_pointer) && (core_rb_valid && core_rb_ready)) begin
       received_all_nest_insns_d = 1'b1;
     end else if (nest_ends) begin
       received_all_nest_insns_d = 1'b0;
@@ -432,20 +434,20 @@ module snitch_sequencer import snitch_pkg::*; #(
     nest_cfg_d = nest_cfg_q;
     loop_cnt_d = loop_cnt_q;
 
+    if (nest_ends) begin
+      loop_cnt_d = 0;
+    end
+
     if (core_frep_valid && core_frep_ready) begin
-      nest_cfg_d[loop_cnt_q].is_streamctl = inp_qdata_op_i[31];
-      nest_cfg_d[loop_cnt_q].max_inst = inp_qdata_op_i[20+:DepthBits];
-      nest_cfg_d[loop_cnt_q].stagger_max = inp_qdata_op_i[14:12];
-      nest_cfg_d[loop_cnt_q].stagger_mask = inp_qdata_op_i[11:8];
-      nest_cfg_d[loop_cnt_q].max_iter = inp_qdata_arga_i[LoopIterBits-1:0];
-      nest_cfg_d[loop_cnt_q].base_pointer = rb_wptr;
+      nest_cfg_d[loop_cnt_d].is_streamctl = inp_qdata_op_i[31];
+      nest_cfg_d[loop_cnt_d].max_inst = inp_qdata_op_i[20+:DepthBits];
+      nest_cfg_d[loop_cnt_d].stagger_max = inp_qdata_op_i[14:12];
+      nest_cfg_d[loop_cnt_d].stagger_mask = inp_qdata_op_i[11:8];
+      nest_cfg_d[loop_cnt_d].max_iter = inp_qdata_arga_i[LoopIterBits-1:0];
+      nest_cfg_d[loop_cnt_d].base_pointer = rb_wptr;
 
       loop_cnt_d = loop_cnt_q + 1;
     end
-
-    if (nest_ends) begin
-      loop_cnt_d = 0;
-    end
   end
 
   //--- Inner loops in last iteration detector ---
@@ -515,7 +517,7 @@ module snitch_sequencer import snitch_pkg::*; #(
   loop_idx_t outermost_ending_loop;
   logic [NestDepth-1:0] loop_ends;
   logic [NestDepth-1:0] loop_active;
-  logic no_loop_ends, all_loops_end;
+  logic no_loop_ends;
 
   // Mask to select only loops which end on current instruction
   assign loop_ends = last_inst & last_iter & last_iter_inner_loops;
@@ -702,10 +704,10 @@ module snitch_sequencer import snitch_pkg::*; #(
   // pragma translate_off
   assign trace_port_o.source    = snitch_pkg::SrcFpuSeq;
   assign trace_port_o.cbuf_push = core_frep_valid && core_frep_ready;
-  assign trace_port_o.max_inst  = nest_cfg_d[loop_cnt_q].max_inst;
-  assign trace_port_o.max_iter  = nest_cfg_d[loop_cnt_q].max_iter;
-  assign trace_port_o.stg_max   = nest_cfg_d[loop_cnt_q].stagger_max;
-  assign trace_port_o.stg_mask  = nest_cfg_d[loop_cnt_q].stagger_mask;
+  assign trace_port_o.max_inst  = inp_qdata_op_i[20+:DepthBits];
+  assign trace_port_o.max_iter  = inp_qdata_arga_i[LoopIterBits-1:0];
+  assign trace_port_o.stg_max   = inp_qdata_op_i[14:12];
+  assign trace_port_o.stg_mask  = inp_qdata_op_i[11:8];
   // pragma translate_on
 
   ////////////////