vrtsim: Enable batch processing in perform_channel_modelling

In perfrom_channel_modelling, do convolution in batches which allows
vrtsim to write the channel samples as they are being produced instead
of waiting for the last sample in the slot to be ready.

radio/vrtsim/vrtsim.c

@@ -372,6 +372,8 @@ typedef struct {
   int nbAnt;
   int flags;
   int aarx;
+  int batch_size;
+  int num_batches;
   c16_t saved_samples[MAX_NUM_ANTENNAS_TX][SAVED_SAMPLES_LEN];
 } channel_modelling_args_t;
 
@@ -415,8 +417,14 @@ static void perform_channel_modelling(void *arg)
     }
   }
 
+  for (int batch_index = 0; batch_index < channel_modelling_args->num_batches; batch_index++) {
+    int start_sample = batch_index * channel_modelling_args->batch_size;
+    int num_samples = min(channel_modelling_args->batch_size, nsamps - start_sample);
+    if (start_sample >= nsamps) {
+      break;
+    }
     for (int aatx = 0; aatx < nb_tx_ant; aatx++) {
-    for (int i = 0; i < nsamps; i++) {
+      for (int i = start_sample; i < start_sample + num_samples; i++) {
         cf_t *impulse_response = channel_impulse_response_p[aatx];
         for (int l = 0; l < channel_desc->channel_length; l++) {
           int idx = i - l;
@@ -458,6 +466,7 @@ static void perform_channel_modelling(void *arg)
                           channel_modelling_args->flags,
                           aarx);
   }
+}
 
 static int vrtsim_write_with_chanmod(vrtsim_state_t *vrtsim_state,
                                      openair0_timestamp timestamp,
@@ -470,6 +479,7 @@ static int vrtsim_write_with_chanmod(vrtsim_state_t *vrtsim_state,
   static c16_t saved_samples[MAX_NUM_ANTENNAS_TX][SAVED_SAMPLES_LEN] __attribute__((aligned(32))) = {0};
   // Indicates what samples are saves in saved_samples
   static openair0_timestamp last_timestamp = 0;
+  const int batch_size = 4096;
 
   AssertFatal(nbAnt <= MAX_NUM_ANTENNAS_TX, "Number of antennas %d exceeds maximum %d\n", nbAnt, MAX_NUM_ANTENNAS_TX);
   for (int aarx = 0; aarx < vrtsim_state->peer_info.num_rx_antennas; aarx++) {
@@ -481,6 +491,8 @@ static int vrtsim_write_with_chanmod(vrtsim_state_t *vrtsim_state,
     args->nbAnt = nbAnt;
     args->flags = flags;
     args->aarx = aarx;
+    args->batch_size = batch_size;
+    args->num_batches = (nsamps + batch_size - 1) / batch_size;
     for (int i = 0; i < nbAnt; i++) {
       args->samples[i] = samplesVoid[i];
     }