drivers: ieee802154_kw41z: Create a fake ACK frame for upper layers

Upper layers like OpenThread expect the radio driver to forward ACK
frame received by the radio.
Simulate this behavior on kw41z by recreating the ACK frame from the
available data.

Signed-off-by: Robert Lubos <[email protected]>

Author: rlubos

drivers/ieee802154/ieee802154_kw41z.c

@@ -155,6 +155,8 @@ struct kw41z_context {
 
 	u32_t rx_warmup_time;
 	u32_t tx_warmup_time;
+
+	bool frame_pending; /* FP bit state from the most recent ACK frame. */
 };
 
 static struct kw41z_context kw41z_context_data;
@@ -569,6 +571,47 @@ static inline void kw41z_rx(struct kw41z_context *kw41z, u8_t len)
 	}
 }
 
+#define ACK_FRAME_LEN 3
+#define ACK_FRAME_TYPE (2 << 0)
+#define ACK_FRAME_PENDING_BIT (1 << 4)
+
+static void handle_ack(struct kw41z_context *kw41z, u8_t seq_number)
+{
+	struct net_pkt *ack_pkt;
+	u8_t ack_psdu[ACK_FRAME_LEN];
+
+	ack_pkt = net_pkt_alloc_with_buffer(kw41z->iface, ACK_FRAME_LEN,
+					    AF_UNSPEC, 0, K_NO_WAIT);
+	if (!ack_pkt) {
+		LOG_ERR("No free packet available.");
+		return;
+	}
+
+	/* Re-create ACK frame. */
+	ack_psdu[0] = kw41z_context_data.frame_pending ?
+		      ACK_FRAME_TYPE | ACK_FRAME_PENDING_BIT : ACK_FRAME_TYPE;
+	ack_psdu[1] = 0;
+	ack_psdu[2] = seq_number;
+
+	if (net_pkt_write(ack_pkt, ack_psdu, sizeof(ack_psdu)) < 0) {
+		LOG_ERR("Failed to write to a packet.");
+		goto out;
+	}
+
+	/* Use some fake values for LQI and RSSI. */
+	(void)net_pkt_set_ieee802154_lqi(ack_pkt, 80);
+	(void)net_pkt_set_ieee802154_rssi(ack_pkt, -40);
+
+	net_pkt_cursor_init(ack_pkt);
+
+	if (ieee802154_radio_handle_ack(kw41z->iface, ack_pkt) != NET_OK) {
+		LOG_INF("ACK packet not handled - releasing.");
+	}
+
+out:
+	net_pkt_unref(ack_pkt);
+}
+
 static int kw41z_tx(struct device *dev, struct net_pkt *pkt,
 		    struct net_buf *frag)
 {
@@ -653,6 +696,10 @@ static int kw41z_tx(struct device *dev, struct net_pkt *pkt,
 	irq_unlock(key);
 	k_sem_take(&kw41z->seq_sync, K_FOREVER);
 
+	if ((kw41z->seq_retval == 0) && ieee802154_is_ar_flag_set(frag)) {
+		handle_ack(kw41z, frag->data[2]);
+	}
+
 	LOG_DBG("seq_retval: %d", kw41z->seq_retval);
 	return kw41z->seq_retval;
 }
@@ -795,6 +842,9 @@ static void kw41z_isr(int unused)
 			case KW41Z_STATE_TXRX:
 				LOG_DBG("TXRX seq done");
 				kw41z_tmr3_disable();
+				/* Store the frame pending bit status. */
+				kw41z_context_data.frame_pending =
+					irqsts & ZLL_IRQSTS_RX_FRM_PEND_MASK;
 			case KW41Z_STATE_TX:
 				LOG_DBG("TX seq done");
 				KW_DBG_TRACE(KW41_DBG_TRACE_TX, irqsts,