Fix breakdown model forbidden value 0 error

When a event causes a new value in the sort module, the first time it
will write all output values, which most of them will be zero. Writting
a zero value is forbidden by default, so we relax the constraint with
the PRV_ZERO flag.

CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Fix breakdown model error that was preventing a zero value to be written in
+  the PRV trace.
+
 ## [1.9.0] - 2024-04-25
 
 ### Added

src/emu/nanos6/breakdown.c

@@ -1,4 +1,4 @@
-/* Copyright (c) 2023 Barcelona Supercomputing Center (BSC)
+/* Copyright (c) 2023-2024 Barcelona Supercomputing Center (BSC)
  * SPDX-License-Identifier: GPL-3.0-or-later */
 
 #include "breakdown.h"
@@ -239,6 +239,11 @@ model_nanos6_breakdown_connect(struct emu *emu)
 		long type = PRV_NANOS6_BREAKDOWN;
 		long flags = PRV_SKIPDUP;
 
+		/* We may emit zero at the start, when an input changes and all
+		 * the other sort output channels write a zero in the output,
+		 * before the last value is set in prv.c. */
+		flags |= PRV_ZERO;
+
 		struct chan *out = sort_get_output(&bemu->sort, i);
 		if (prv_register(prv, i, type, bay, out, flags)) {
 			err("prv_register failed");