[mac] add capability to transition from Sleep to Transmit during data request (#4697)

examples/platforms/nrf528xx/src/radio.c

@@ -428,7 +428,8 @@ otRadioCaps otPlatRadioGetCaps(otInstance *aInstance)
 {
     OT_UNUSED_VARIABLE(aInstance);
 
-    return (otRadioCaps)(OT_RADIO_CAPS_ENERGY_SCAN | OT_RADIO_CAPS_ACK_TIMEOUT | OT_RADIO_CAPS_CSMA_BACKOFF);
+    return (otRadioCaps)(OT_RADIO_CAPS_ENERGY_SCAN | OT_RADIO_CAPS_ACK_TIMEOUT | OT_RADIO_CAPS_CSMA_BACKOFF |
+                         OT_RADIO_CAPS_SLEEP_TO_TX);
 }
 
 bool otPlatRadioGetPromiscuous(otInstance *aInstance)

include/openthread/platform/radio.h

@@ -123,6 +123,7 @@ enum
     OT_RADIO_CAPS_ENERGY_SCAN      = 1 << 1, ///< Radio supports Energy Scans.
     OT_RADIO_CAPS_TRANSMIT_RETRIES = 1 << 2, ///< Radio supports tx retry logic with collision avoidance (CSMA).
     OT_RADIO_CAPS_CSMA_BACKOFF     = 1 << 3, ///< Radio supports CSMA backoff for frame transmission (but no retry).
+    OT_RADIO_CAPS_SLEEP_TO_TX      = 1 << 4, ///< Radio supports direct transition from sleep to TX with CSMA.
 };
 
 #define OT_PANID_BROADCAST 0xffff ///< IEEE 802.15.4 Broadcast PAN ID
@@ -244,6 +245,10 @@ typedef enum otRadioState
  *  +----------+  Disable() +-------+   Sleep()  +---------+   Receive()   +----------+
  *                                    (Radio OFF)                 or
  *                                                        signal TransmitDone
+ *
+ * During the IEEE 802.15.4 data request command the transition Sleep->Receive->Transmit
+ * can be shortened to direct transition from Sleep to Transmit if the platform supports
+ * the OT_RADIO_CAPS_SLEEP_TO_TX capability.
  */
 
 /**
@@ -558,7 +563,9 @@ otRadioFrame *otPlatRadioGetTransmitBuffer(otInstance *aInstance);
  * requesting transmission.  The channel and transmit power are also included in the otRadioFrame structure.
  *
  * The transmit sequence consists of:
- * 1. Transitioning the radio to Transmit from Receive.
+ * 1. Transitioning the radio to Transmit from one of the following states:
+ *    - Receive if RX is on when the device is idle or OT_RADIO_CAPS_SLEEP_TO_TX is not supported
+ *    - Sleep if RX is off when the device is idle and OT_RADIO_CAPS_SLEEP_TO_TX is supported.
  * 2. Transmits the psdu on the given channel and at the given transmit power.
  *
  * @param[in] aInstance  The OpenThread instance structure.

src/core/mac/sub_mac.cpp

@@ -285,8 +285,11 @@ void SubMac::BeginTransmit(void)
         mTransmitFrame.SetCsmaCaEnabled(true);
     }
 
-    error = Get<Radio>().Receive(mTransmitFrame.GetChannel());
-    OT_ASSERT(error == OT_ERROR_NONE);
+    if ((mRadioCaps & OT_RADIO_CAPS_SLEEP_TO_TX) == 0)
+    {
+        error = Get<Radio>().Receive(mTransmitFrame.GetChannel());
+        OT_ASSERT(error == OT_ERROR_NONE);
+    }
 
     SetState(kStateTransmit);