From bb80652885b216a770e07c298e1e380bdf5fe08a Mon Sep 17 00:00:00 2001
From: Matthias Ringwald <matthias@ringwald.ch>
Date: Sun, 19 Jan 2020 00:39:55 +0100
Subject: [PATCH] hci_transport_h4: avoid uart read for empty payload

---
 src/hci_transport_h4.c | 75 +++++++++++++++++++++++-------------------
 1 file changed, 41 insertions(+), 34 deletions(-)

diff --git a/src/hci_transport_h4.c b/src/hci_transport_h4.c
index e9f9d5877..4d6d1def8 100644
--- a/src/hci_transport_h4.c
+++ b/src/hci_transport_h4.c
@@ -187,9 +187,42 @@ static void hci_transport_h4_trigger_next_read(void){
     btstack_uart->receive_block(&hci_packet[read_pos], bytes_to_read);  
 }
 
-static void hci_transport_h4_block_read(void){
+static void hci_transport_h4_packet_complete(void){
+#ifdef ENABLE_BAUDRATE_CHANGE_FLOWCONTROL_BUG_WORKAROUND
+    if (baudrate_change_workaround_state == BAUDRATE_CHANGE_WORKAROUND_IDLE
+            && memcmp(hci_packet, local_version_event_prefix, sizeof(local_version_event_prefix)) == 0){
+#ifdef ENABLE_CC256X_BAUDRATE_CHANGE_FLOWCONTROL_BUG_WORKAROUND
+                if (little_endian_read_16(hci_packet, 11) == BLUETOOTH_COMPANY_ID_TEXAS_INSTRUMENTS_INC){
+                    // detect TI CC256x controller based on manufacturer
+                    log_info("Detected CC256x controller");
+                    baudrate_change_workaround_state = BAUDRATE_CHANGE_WORKAROUND_CHIPSET_DETECTED;
+                } else {
+                    // work around not needed
+                    log_info("Bluetooth controller not by TI");
+                    baudrate_change_workaround_state = BAUDRATE_CHANGE_WORKAROUND_DONE;
+                }
+#endif
+#ifdef ENABLE_CYPRESS_BAUDRATE_CHANGE_FLOWCONTROL_BUG_WORKAROUND
+                if (little_endian_read_16(hci_packet, 11) == BLUETOOTH_COMPANY_ID_CYPRESS_SEMICONDUCTOR){
+                    // detect Cypress controller based on manufacturer
+                    log_info("Detected Cypress controller");
+                    baudrate_change_workaround_state = BAUDRATE_CHANGE_WORKAROUND_CHIPSET_DETECTED;
+                } else {
+                    // work around not needed
+                    log_info("Bluetooth controller not by Cypress");
+                    baudrate_change_workaround_state = BAUDRATE_CHANGE_WORKAROUND_DONE;
+                }
+#endif
+            }
+#endif
+    uint16_t packet_len = read_pos-1;
 
-    uint16_t packet_len;
+    // reset state machine before delivering packet to stack as it might close the transport
+    hci_transport_h4_reset_statemachine();
+    packet_handler(hci_packet[0], &hci_packet[1], packet_len);
+}
+
+static void hci_transport_h4_block_read(void){
 
     read_pos += bytes_to_read;
 
@@ -258,38 +291,7 @@ static void hci_transport_h4_block_read(void){
             break;
 
         case H4_W4_PAYLOAD:
-#ifdef ENABLE_BAUDRATE_CHANGE_FLOWCONTROL_BUG_WORKAROUND
-            if (baudrate_change_workaround_state == BAUDRATE_CHANGE_WORKAROUND_IDLE
-            && memcmp(hci_packet, local_version_event_prefix, sizeof(local_version_event_prefix)) == 0){
-#ifdef ENABLE_CC256X_BAUDRATE_CHANGE_FLOWCONTROL_BUG_WORKAROUND
-                if (little_endian_read_16(hci_packet, 11) == BLUETOOTH_COMPANY_ID_TEXAS_INSTRUMENTS_INC){
-                    // detect TI CC256x controller based on manufacturer
-                    log_info("Detected CC256x controller");
-                    baudrate_change_workaround_state = BAUDRATE_CHANGE_WORKAROUND_CHIPSET_DETECTED;
-                } else {
-                    // work around not needed
-                    log_info("Bluetooth controller not by TI");
-                    baudrate_change_workaround_state = BAUDRATE_CHANGE_WORKAROUND_DONE;
-                }
-#endif
-#ifdef ENABLE_CYPRESS_BAUDRATE_CHANGE_FLOWCONTROL_BUG_WORKAROUND
-                if (little_endian_read_16(hci_packet, 11) == BLUETOOTH_COMPANY_ID_CYPRESS_SEMICONDUCTOR){
-                    // detect Cypress controller based on manufacturer
-                    log_info("Detected Cypress controller");
-                    baudrate_change_workaround_state = BAUDRATE_CHANGE_WORKAROUND_CHIPSET_DETECTED;
-                } else {
-                    // work around not needed
-                    log_info("Bluetooth controller not by Cypress");
-                    baudrate_change_workaround_state = BAUDRATE_CHANGE_WORKAROUND_DONE;
-                }
-#endif
-            }
-#endif
-            packet_len = read_pos-1;
-
-            // reset state machine before delivering packet to stack as it might close the transport
-            hci_transport_h4_reset_statemachine();
-            packet_handler(hci_packet[0], &hci_packet[1], packet_len);
+            hci_transport_h4_packet_complete();
             break;
 
         case H4_OFF:
@@ -306,6 +308,11 @@ static void hci_transport_h4_block_read(void){
     }
 #endif
 
+    // forward packet if payload size == 0
+    if (h4_state == H4_W4_PAYLOAD && bytes_to_read == 0) {
+        hci_transport_h4_packet_complete();
+    }
+
     if (h4_state != H4_OFF) {
         hci_transport_h4_trigger_next_read();
     }