nimble/phy: Add support for variable T_ifs

This enables APIs to support variable T_ifs in PHY. By default 150us is
used but this value can be changed before each transition. After
transition value is reset to default so LL does not need to care about
setting T_ifs everywhere.

This may be useful for scheduling of related events with tight timings.

Disabled by default since it allows for compile-time optimizations.

nimble/controller/include/controller/ble_phy.h

@@ -87,6 +87,11 @@ int ble_phy_init(void);
 /* Set the PHY channel */
 int ble_phy_setchan(uint8_t chan, uint32_t access_addr, uint32_t crcinit);
 
+#if MYNEWT_VAL(BLE_PHY_VARIABLE_TIFS)
+/* Set T_ifs time for next transition */
+void ble_phy_tifs_set(uint16_t tifs);
+#endif
+
 /* Set transmit start time */
 int ble_phy_tx_set_start_time(uint32_t cputime, uint8_t rem_usecs);
 

nimble/drivers/nrf52/src/ble_phy.c

@@ -140,6 +140,9 @@ struct ble_phy_obj
     void *txend_arg;
     ble_phy_tx_end_func txend_cb;
     uint32_t phy_start_cputime;
+#if MYNEWT_VAL(BLE_PHY_VARIABLE_TIFS)
+    uint16_t tifs;
+#endif
 };
 struct ble_phy_obj g_ble_phy_data;
 
@@ -642,6 +645,26 @@ nrf_wait_disabled(void)
     }
 }
 
+#if MYNEWT_VAL(BLE_PHY_VARIABLE_TIFS)
+static uint16_t
+ble_phy_tifs_get(void)
+{
+    return g_ble_phy_data.tifs;
+}
+
+void
+ble_phy_tifs_set(uint16_t tifs)
+{
+    g_ble_phy_data.tifs = tifs;
+}
+#else
+static uint16_t
+ble_phy_tifs_get(void)
+{
+    return BLE_LL_IFS;
+}
+#endif
+
 /**
  *
  *
@@ -796,7 +819,7 @@ ble_phy_wfr_enable(int txrx, uint8_t tx_phy_mode, uint32_t wfr_usecs)
 
     if (txrx == BLE_PHY_WFR_ENABLE_TXRX) {
         /* RX shall start exactly T_IFS after TX end captured in CC[2] */
-        end_time = NRF_TIMER0->CC[2] + BLE_LL_IFS;
+        end_time = NRF_TIMER0->CC[2] + ble_phy_tifs_get();
         /* Adjust for delay between EVENT_END and actual TX end time */
         end_time += g_ble_phy_t_txenddelay[tx_phy_mode];
         /* Wait a bit longer due to allowed active clock accuracy */
@@ -1015,7 +1038,7 @@ ble_phy_tx_end_isr(void)
         ble_phy_wfr_enable(BLE_PHY_WFR_ENABLE_TXRX, tx_phy_mode, 0);
 
         /* Schedule RX exactly T_IFS after TX end captured in CC[2] */
-        rx_time = NRF_TIMER0->CC[2] + BLE_LL_IFS;
+        rx_time = NRF_TIMER0->CC[2] + ble_phy_tifs_get();
         /* Adjust for delay between EVENT_END and actual TX end time */
         rx_time += g_ble_phy_t_txenddelay[tx_phy_mode];
         /* Adjust for radio ramp-up */
@@ -1030,7 +1053,7 @@ ble_phy_tx_end_isr(void)
         ble_phy_plna_enable_lna();
     } else if (transition == BLE_PHY_TRANSITION_TX_TX) {
         /* Schedule TX exactly T_IFS after TX end captured in CC[2] */
-        tx_time = NRF_TIMER0->CC[2] + BLE_LL_IFS;
+        tx_time = NRF_TIMER0->CC[2] + ble_phy_tifs_get();
         /* Adjust for delay between EVENT_END and actual TX end time */
         tx_time += g_ble_phy_t_txenddelay[tx_phy_mode];
         /* Adjust for radio ramp-up */
@@ -1161,7 +1184,7 @@ ble_phy_rx_end_isr(void)
      */
 
     /* Schedule TX exactly T_IFS after RX end captured in CC[2] */
-    tx_time = NRF_TIMER0->CC[2] + BLE_LL_IFS;
+    tx_time = NRF_TIMER0->CC[2] + ble_phy_tifs_get();
     /* Adjust for delay between actual RX end time and EVENT_END */
     tx_time -= g_ble_phy_t_rxenddelay[ble_hdr->rxinfo.phy_mode];
     /* Adjust for radio ramp-up */
@@ -1379,6 +1402,10 @@ ble_phy_isr(void)
         NRF_RADIO->EVENTS_DISABLED = 0;
         nrf_radio_int_disable(NRF_RADIO, RADIO_INTENCLR_DISABLED_Msk);
 
+#if MYNEWT_VAL(BLE_PHY_VARIABLE_TIFS)
+        g_ble_phy_data.tifs = BLE_LL_IFS;
+#endif
+
         switch (g_ble_phy_data.phy_state) {
         case BLE_PHY_STATE_RX:
 #if MYNEWT_VAL(BLE_LL_LNA)
@@ -1524,6 +1551,10 @@ ble_phy_init(void)
     /* Set phy channel to an invalid channel so first set channel works */
     g_ble_phy_data.phy_chan = BLE_PHY_NUM_CHANS;
 
+#if MYNEWT_VAL(BLE_PHY_VARIABLE_TIFS)
+    g_ble_phy_data.tifs = BLE_LL_IFS;
+#endif
+
     /* Toggle peripheral power to reset (just in case) */
     nrf_radio_power_set(NRF_RADIO, false);
     nrf_radio_power_set(NRF_RADIO, true);

nimble/drivers/nrf52/syscfg.yml

@@ -17,6 +17,15 @@
 #
 
 syscfg.defs:
+    BLE_PHY_VARIABLE_TIFS:
+        description: >
+            Enables API to set custom T_ifs (inter-frame spacing) for each
+            transition. T_ifs is reset to default value after each transition.
+            When disabled, 150us is always used which enables some build-time
+            optimizations by compiler.
+        experimental: 1
+        value: 0
+
     BLE_PHY_SYSVIEW:
         description: >
             Enable SystemView tracing module for radio driver.