Harald Welte has submitted this change and it was merged.

Change subject: trxcon/scheduler: transmit dummy frames on CBTX lchans
......................................................................


trxcon/scheduler: transmit dummy frames on CBTX lchans

If at the moment of transmission there are no frames in TX buffer,
then either a dummy LAPDm frame (0x01, 0x03, 0x01, 0x2b ...) or a
silence frame (depending on a codec in use) shall be transmitted.
This is required for proper measurements on the BTS side.

Change-Id: Ie590990f2274ea476678f6b2079f90eeadab6501
---
M src/host/trxcon/sched_prim.c
M src/host/trxcon/sched_trx.c
M src/host/trxcon/sched_trx.h
M src/host/trxcon/trxcon.c
4 files changed, 118 insertions(+), 0 deletions(-)

Approvals:
  Harald Welte: Looks good to me, approved
  Jenkins Builder: Verified



diff --git a/src/host/trxcon/sched_prim.c b/src/host/trxcon/sched_prim.c
index fb5f0a0..c17fb2a 100644
--- a/src/host/trxcon/sched_prim.c
+++ b/src/host/trxcon/sched_prim.c
@@ -23,6 +23,7 @@
  */
 
 #include <errno.h>
+#include <stdlib.h>
 #include <string.h>
 #include <talloc.h>
 
@@ -31,6 +32,7 @@
 #include <osmocom/core/linuxlist.h>
 
 #include <osmocom/gsm/protocol/gsm_04_08.h>
+#include <osmocom/gsm/protocol/gsm_08_58.h>
 
 #include "scheduler.h"
 #include "sched_trx.h"
@@ -227,6 +229,93 @@
 }
 
 /**
+ * Assigns a dummy primitive to a lchan depending on its type.
+ * Could be used when there is nothing to transmit, but
+ * CBTX (Continuous Burst Transmission) is assumed.
+ *
+ * @param  lchan lchan to assign a primitive
+ * @return       zero in case of success, otherwise a error code
+ */
+int sched_prim_dummy(struct trx_lchan_state *lchan)
+{
+       enum trx_lchan_type chan = lchan->type;
+       uint8_t tch_mode = lchan->tch_mode;
+       struct trx_ts_prim *prim;
+       uint8_t prim_buffer[40];
+       size_t prim_len = 0;
+       int i;
+
+       /**
+        * TS 144.006, section 8.4.2.3 "Fill frames"
+        * A fill frame is a UI command frame for SAPI 0, P=0
+        * and with an information field of 0 octet length.
+        */
+       static const uint8_t lapdm_fill_frame[] = {
+               0x01, 0x03, 0x01,
+               /* Pending part is to be randomized */
+       };
+
+       /* Make sure that there is no existing primitive */
+       OSMO_ASSERT(lchan->prim == NULL);
+
+       /**
+        * Determine what actually should be generated:
+        * TCH in GSM48_CMODE_SIGN: LAPDm fill frame;
+        * TCH in other modes: silence frame;
+        * other channels: LAPDm fill frame.
+        */
+       if (CHAN_IS_TCH(chan) && TCH_MODE_IS_SPEECH(tch_mode)) {
+               /**
+                * Silence frame indication
+                * HACK: use actual rsl_cmode!
+                */
+               prim_len = sched_bad_frame_ind(prim_buffer,
+                       RSL_CMOD_SPD_SPEECH, tch_mode);
+       } else if (CHAN_IS_TCH(chan) && TCH_MODE_IS_DATA(tch_mode)) {
+               /* FIXME: should we do anything for CSD? */
+               return 0;
+       } else {
+               /**
+                * TS 144.006, section 8.1.2.3 "Fill frames"
+                * A fill frame is a UI command frame for SAPI 0, P=0
+                * and with an information field of 0 octet length.
+                */
+               memcpy(prim_buffer, lapdm_fill_frame, 3);
+
+               /* Randomize pending unused bytes */
+               for (i = 3; i < GSM_MACBLOCK_LEN; i++)
+                       prim_buffer[i] = (uint8_t) rand();
+
+               /* Define a prim length */
+               prim_len = GSM_MACBLOCK_LEN;
+       }
+
+       /* Nothing to allocate / assign */
+       if (!prim_len)
+               return 0;
+
+       /* Allocate a new primitive */
+       prim = talloc_zero_size(lchan, sizeof(struct trx_ts_prim) + prim_len);
+       if (prim == NULL)
+               return -ENOMEM;
+
+       /* Init primitive header */
+       prim->payload_len = prim_len;
+       prim->chan = lchan->type;
+
+       /* Fill in the payload */
+       memcpy(prim->payload, prim_buffer, prim_len);
+
+       /* Assign the current prim */
+       lchan->prim = prim;
+
+       LOGP(DSCHD, LOGL_DEBUG, "Transmitting a dummy / silence frame "
+               "on lchan=%s\n", trx_lchan_desc[chan].name);
+
+       return 0;
+}
+
+/**
  * Flushes a queue of primitives
  *
  * @param list list of prims going to be flushed
diff --git a/src/host/trxcon/sched_trx.c b/src/host/trxcon/sched_trx.c
index 8c859de..168c4ef 100644
--- a/src/host/trxcon/sched_trx.c
+++ b/src/host/trxcon/sched_trx.c
@@ -97,6 +97,19 @@
                if (lchan->prim == NULL)
                        lchan->prim = sched_prim_dequeue(&ts->tx_prims, chan);
 
+               /* TODO: report TX buffers health to the higher layers */
+
+               /* If CBTX (Continuous Burst Transmission) is assumed */
+               if (trx_lchan_desc[chan].flags & TRX_CH_FLAG_CBTX) {
+                       /**
+                        * Probably, a TX buffer is empty. Nevertheless,
+                        * we shall continuously transmit anything on
+                        * CBTX channels.
+                        */
+                       if (lchan->prim == NULL)
+                               sched_prim_dummy(lchan);
+               }
+
                /* If there is no primitive, do nothing */
                if (lchan->prim == NULL)
                        continue;
diff --git a/src/host/trxcon/sched_trx.h b/src/host/trxcon/sched_trx.h
index 6a02543..d9e0c8e 100644
--- a/src/host/trxcon/sched_trx.h
+++ b/src/host/trxcon/sched_trx.h
@@ -275,6 +275,17 @@
 int sched_prim_push(struct trx_instance *trx,
        struct trx_ts_prim *prim, uint8_t chan_nr);
 
+#define TCH_MODE_IS_SPEECH(mode)       \
+         (mode == GSM48_CMODE_SPEECH_V1   \
+       || mode == GSM48_CMODE_SPEECH_EFR  \
+       || mode == GSM48_CMODE_SPEECH_AMR)
+
+#define TCH_MODE_IS_DATA(mode)        \
+         (mode == GSM48_CMODE_DATA_14k5  \
+       || mode == GSM48_CMODE_DATA_12k0  \
+       || mode == GSM48_CMODE_DATA_6k0   \
+       || mode == GSM48_CMODE_DATA_3k6)
+
 #define CHAN_IS_TCH(chan) \
        (chan == TRXC_TCHF || chan == TRXC_TCHH_0 || chan == TRXC_TCHH_1)
 
@@ -286,6 +297,7 @@
 
 struct trx_ts_prim *sched_prim_dequeue(struct llist_head *queue,
        enum trx_lchan_type lchan_type);
+int sched_prim_dummy(struct trx_lchan_state *lchan);
 void sched_prim_drop(struct trx_lchan_state *lchan);
 void sched_prim_flush_queue(struct llist_head *list);
 
diff --git a/src/host/trxcon/trxcon.c b/src/host/trxcon/trxcon.c
index 5542240..43c98a5 100644
--- a/src/host/trxcon/trxcon.c
+++ b/src/host/trxcon/trxcon.c
@@ -28,6 +28,7 @@
 #include <getopt.h>
 #include <unistd.h>
 #include <signal.h>
+#include <time.h>
 
 #include <arpa/inet.h>
 
@@ -293,6 +294,9 @@
                }
        }
 
+       /* Initialize pseudo-random generator */
+       srand(time(NULL));
+
        while (!app_data.quit)
                osmo_select_main(0);
 

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Gerrit-MessageType: merged
Gerrit-Change-Id: Ie590990f2274ea476678f6b2079f90eeadab6501
Gerrit-PatchSet: 3
Gerrit-Project: osmocom-bb
Gerrit-Branch: fixeria/trx
Gerrit-Owner: Vadim Yanitskiy <axilira...@gmail.com>
Gerrit-Reviewer: Harald Welte <lafo...@gnumonks.org>
Gerrit-Reviewer: Jenkins Builder

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