mac: simplify BSR packing logic

simplify logic to check whether a BSR fits and, if so, which type.
before the check has been done in two places.

we now also accomodate for the CE subheader size.

lib/include/srslte/mac/pdu.h

@@ -33,6 +33,8 @@ class subh;
 
 namespace srslte {
 
+#define CE_SUBHEADER_LEN (1)
+
 /* 3GPP 36.321 Table 6.2.1-1 */
 enum class dl_sch_lcid {
   CCCH     = 0b00000,

lib/src/mac/pdu.cc

@@ -82,7 +82,7 @@ uint32_t ce_size(dl_sch_lcid v)
 
 uint32_t ce_subheader_size(dl_sch_lcid v)
 {
-  return 1;
+  return CE_SUBHEADER_LEN;
 }
 
 uint32_t ce_total_size(dl_sch_lcid v)

srsue/src/stack/mac/proc_bsr.cc

@@ -219,9 +219,9 @@ uint32_t bsr_proc::get_buffer_state_lcg(uint32_t lcg)
   return n;
 }
 
-bool bsr_proc::generate_bsr(bsr_t* bsr, uint32_t nof_padding_bytes)
+bool bsr_proc::generate_bsr(bsr_t* bsr, uint32_t pdu_space)
 {
-  bool     ret     = false;
+  bool     send_bsr = false;
   uint32_t nof_lcg = 0;
   bzero(bsr, sizeof(bsr_t));
 
@@ -230,13 +230,22 @@ bool bsr_proc::generate_bsr(bsr_t* bsr, uint32_t nof_padding_bytes)
     bsr->buff_size[i] = get_buffer_state_lcg(i);
     if (bsr->buff_size[i] > 0) {
       nof_lcg++;
-      ret = true;
     }
   }
-  if (triggered_bsr_type == PADDING) {
+
-    if (nof_padding_bytes < 4) {
+  if (pdu_space >= CE_SUBHEADER_LEN + ce_size(srslte::ul_sch_lcid::LONG_BSR)) {
-      // If space only for short
+    // we could fit a long BSR
+    if (triggered_bsr_type != PADDING && nof_lcg <= 1) {
+      // for Regular and periodic BSR we still send a short BSR if only one LCG has data to send
+      bsr->format = SHORT_BSR;
+    } else {
+      bsr->format = LONG_BSR;
+    }
+    send_bsr = true;
+  } else if (pdu_space >= CE_SUBHEADER_LEN + ce_size(srslte::ul_sch_lcid::SHORT_BSR)) {
+    // we can only fit a short or truncated BSR
     if (nof_lcg > 1) {
+      // only send truncated BSR for a padding BSR
       bsr->format           = TRUNC_BSR;
       uint32_t max_prio_lcg = find_max_priority_lcg_with_data();
       for (uint32_t i = 0; i < NOF_LCG; i++) {
@@ -247,16 +256,10 @@ bool bsr_proc::generate_bsr(bsr_t* bsr, uint32_t nof_padding_bytes)
     } else {
       bsr->format = SHORT_BSR;
     }
-    } else {
+    send_bsr = true;
-      // If space for long BSR
-      bsr->format = LONG_BSR;
-    }
-  } else {
-    bsr->format = SHORT_BSR;
-    if (nof_lcg > 1) {
-      bsr->format = LONG_BSR;
-    }
   }
+
+  if (send_bsr) {
     Info("BSR:   Type %s, Format %s, Value=%d,%d,%d,%d\n",
          bsr_type_tostring(triggered_bsr_type),
          bsr_format_tostring(bsr->format),
@@ -270,8 +273,9 @@ bool bsr_proc::generate_bsr(bsr_t* bsr, uint32_t nof_padding_bytes)
       timer_periodic.run();
       Debug("BSR:   Started periodicBSR-Timer\n");
     }
+  }
 
-  return ret;
+  return send_bsr;
 }
 
 // Checks if Regular BSR must be assembled, as defined in 5.4.5
@@ -332,19 +336,8 @@ bool bsr_proc::need_to_send_bsr_on_ul_grant(uint32_t grant_size, bsr_t* bsr)
 
   bool bsr_included = false;
 
-  uint32_t bsr_sz = 0;
   if (triggered_bsr_type == PERIODIC || triggered_bsr_type == REGULAR) {
-
+    bsr_included = generate_bsr(bsr, grant_size);
-    generate_bsr(bsr, 0);
-
-    // Only include BSR if it can fit into the remaining grant
-    bsr_sz = bsr->format == LONG_BSR ? 3 : 1;
-    if (bsr_sz > grant_size) {
-      Debug("Grant is not enough to accommodate the BSR MAC CE\n");
-    } else {
-      Debug("BSR:   Including Regular BSR: grant_size=%d, bsr_sz=%d\n", grant_size, bsr_sz);
-      bsr_included = true;
-    }
   }
 
   // All triggered BSRs shall be cancelled in case the UL grant can accommodate all pending data available for
@@ -383,7 +376,7 @@ bool bsr_proc::generate_padding_bsr(uint32_t nof_padding_bytes, bsr_t* bsr)
   bool ret = false;
 
   // This function is called by MUX only if Regular BSR has not been triggered before
-  if (nof_padding_bytes >= 2) {
+  if (nof_padding_bytes >= CE_SUBHEADER_LEN + ce_size(srslte::ul_sch_lcid::SHORT_BSR)) {
     // generate padding BSR
     set_trigger(PADDING);
     generate_bsr(bsr, nof_padding_bytes);