From 36207db615cf79b1d4bf9b31456c4653538e33cf Mon Sep 17 00:00:00 2001
From: Xavier Arteaga <xavier@softwareradiosystems.com>
Date: Thu, 19 Aug 2021 15:50:03 +0200
Subject: [PATCH] Added CORESET start_rb helper function

---
 lib/include/srsran/phy/common/phy_common_nr.h | 12 +++++++++++
 lib/src/phy/common/phy_common_nr.c            | 20 +++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/lib/include/srsran/phy/common/phy_common_nr.h b/lib/include/srsran/phy/common/phy_common_nr.h
index 9941df529..bf8270082 100644
--- a/lib/include/srsran/phy/common/phy_common_nr.h
+++ b/lib/include/srsran/phy/common/phy_common_nr.h
@@ -518,6 +518,18 @@ SRSRAN_API uint32_t srsran_coreset_get_bw(const srsran_coreset_t* coreset);
  */
 SRSRAN_API uint32_t srsran_coreset_get_sz(const srsran_coreset_t* coreset);
 
+/**
+ * @brief Calculates the starting resource block index in the resource grid
+ *
+ * @remark Intended to be used for common search space as specifies the lat clause in TS 38.214 section 5.1.2.2 Resource
+ * allocation in frequency domain
+ *
+ * @param coreset provides the given CORESET configuration
+ * @return The index of the lowest resource block in the resource grid used by the given CORESET if the CORESET
+ * configuration is valid; Otherwise, 0.
+ */
+SRSRAN_API uint32_t srsran_coreset_start_rb(const srsran_coreset_t* coreset);
+
 /**
  * @brief Get the NR PDSCH mapping type in string
  * @param mapping_type Mapping type
diff --git a/lib/src/phy/common/phy_common_nr.c b/lib/src/phy/common/phy_common_nr.c
index 9a78bc310..c46dfd222 100644
--- a/lib/src/phy/common/phy_common_nr.c
+++ b/lib/src/phy/common/phy_common_nr.c
@@ -115,6 +115,26 @@ uint32_t srsran_coreset_get_sz(const srsran_coreset_t* coreset)
   return srsran_coreset_get_bw(coreset) * SRSRAN_NRE * coreset->duration;
 }
 
+uint32_t srsran_coreset_start_rb(const srsran_coreset_t* coreset)
+{
+  // Protect CORESET access
+  if (coreset == NULL) {
+    return 0;
+  }
+
+  // Iterates all the possible frequency resources trying to find the first enabled
+  for (uint32_t res = 0; res < SRSRAN_CORESET_FREQ_DOMAIN_RES_SIZE; res++) {
+    // If the frequency resource is enabled...
+    if (coreset->freq_resources[res]) {
+      // ... return the lowest resource block index
+      return 6 * res + coreset->offset_rb;
+    }
+  }
+
+  // Returns the start resource index
+  return 0;
+}
+
 const char* srsran_sch_mapping_type_to_str(srsran_sch_mapping_type_t mapping_type)
 {
   switch (mapping_type) {