NRF_ERROR_RESOURCES 발생하는 경우 패킷을 pending 슬롯에 저장, TX_RDY 이벤트에서만 재전송

- ios에서 BLE 연결 안정성 개선을 위함
- 기존: NRF_ERROR_RESOURCES 발생 시 2ms 간격으로 최대 20회 재시도

project/ble_peripheral/ble_app_bladder_patch/main.c

@@ -562,6 +562,49 @@ extern void maa_async_abort(void);
 static volatile uint8_t  pending_cmd_buf[BLE_NUS_MAX_DATA_LEN] = {0};
 static volatile uint8_t  pending_cmd_len = 0;
 
+static bool ble_retry_pending_tx(void)
+{
+    uint16_t send_len;
+    uint32_t err;
+
+    if (!s_tx_pending)
+    {
+        return true;
+    }
+    if (ble_connection_st != BLE_CONNECTED_ST)
+    {
+        s_tx_pending = false;
+        s_tx_pending_len = 0;
+        return false;
+    }
+
+    send_len = s_tx_pending_len;
+    err = ble_nus_data_send(&m_nus, s_tx_pending_buf, &send_len, m_conn_handle);
+
+    if (err == NRF_SUCCESS)
+    {
+        s_tx_pending = false;
+        s_tx_pending_len = 0;
+        return true;
+    }
+    if (err == NRF_ERROR_RESOURCES)
+    {
+        return false;
+    }
+    if (err == NRF_ERROR_INVALID_STATE || err == NRF_ERROR_NOT_FOUND)
+    {
+        DBG_PRINTF("[BLE TX] Pending send aborted\r\n");
+        s_tx_pending = false;
+        s_tx_pending_len = 0;
+        return false;
+    }
+
+    DBG_PRINTF("[BLE TX] Pending err:0x%X\r\n", err);
+    s_tx_pending = false;
+    s_tx_pending_len = 0;
+    return false;
+}
+
 /**
  * @brief NUS (Nordic UART Service) data receive handler
  *
@@ -601,22 +644,20 @@ static void nus_data_handler(ble_nus_evt_t * p_evt)
     }
     else if (p_evt->type == BLE_NUS_EVT_TX_RDY)
     {
+        /* First drain any queued packet that previously hit NRF_ERROR_RESOURCES. */
+        if (s_tx_pending)
+        {
+            if (!ble_retry_pending_tx())
+            {
+                return;
+            }
+        }
+
         /* BLE TX buffer has space - continue async MAA transmission */
         if (maa_async_is_busy())
         {
             maa_async_on_tx_ready();
         }
-        /* Retry pending packet (dr_binary_tx_safe async) */
-        else if (s_tx_pending)
-        {
-            uint16_t send_len = s_tx_pending_len;
-            uint32_t err = ble_nus_data_send(&m_nus, s_tx_pending_buf, &send_len, m_conn_handle);
-            if (err == NRF_SUCCESS)
-            {
-                s_tx_pending = false;
-            }
-            /* NRF_ERROR_RESOURCES -> retry on next TX_RDY */
-        }
     }
 }
 
@@ -1458,7 +1499,8 @@ void ascii_format_data(uint8_t *buffer, const char *tag, const char *data_ascii,
 /**
  * @brief BLE binary safe transmission (preamble for dr_binary_tx_safe)
  *
- * On NRF_ERROR_RESOURCES (TX queue full), retries at 5ms intervals.
+ * On NRF_ERROR_RESOURCES (TX queue full), stores one pending packet and retries
+ * only when BLE_NUS_EVT_TX_RDY is received.
  * Returns gracefully on connection errors.
  *
  * @param ble_bin_buff Data buffer to transmit
@@ -1507,8 +1549,8 @@ void dr_binary_tx_safe(uint8_t const *ble_bin_buff, uint16_t length)
 {
     uint32_t err_code;
     static uint8_t tx_buffer[BLE_NUS_MAX_DATA_LEN] = {0};
-    uint16_t retry_count = 0;
-    const uint16_t MAX_RETRIES = 20;  /* Max retries: 2ms x 20 = 40ms (was 5ms x 100 = 500ms) */
+    uint16_t send_len;
+    uint16_t total_len;
 
     if (ble_connection_st == 0) return;
 
@@ -1521,37 +1563,36 @@ void dr_binary_tx_safe(uint8_t const *ble_bin_buff, uint16_t length)
         tx_buffer[length * sizeof(uint16_t)]     = (uint8_t)(crc & 0xFF);
         tx_buffer[length * sizeof(uint16_t) + 1] = (uint8_t)((crc >> 8) & 0xFF);
 
-        uint16_t total_len = length * sizeof(uint16_t) + 2;
+        total_len = length * sizeof(uint16_t) + 2;
+        send_len = total_len;
+        err_code = ble_nus_data_send(&m_nus, tx_buffer, &send_len, m_conn_handle);
 
-        do
+        if (err_code == NRF_SUCCESS)
         {
-            uint16_t send_len = total_len;
-            err_code = ble_nus_data_send(&m_nus, tx_buffer, &send_len, m_conn_handle);
-
-            if (err_code == NRF_SUCCESS)
-            {
-                return;
-            }
-            else if (err_code == NRF_ERROR_RESOURCES)
-            {
-                nrf_delay_ms(2);  /* Was 5ms -> 2ms */
-                retry_count++;
-            }
-            else if (err_code == NRF_ERROR_INVALID_STATE || err_code == NRF_ERROR_NOT_FOUND)
-            {
-                DBG_PRINTF("[BLE TX] Disconnected\r\n");
-                return;
-            }
-            else
-            {
-                DBG_PRINTF("[BLE TX] Err:0x%X\r\n", err_code);
-                return;
-            }
-        } while (retry_count < MAX_RETRIES);
-
-        if (retry_count >= MAX_RETRIES)
+            return;
+        }
+        else if (err_code == NRF_ERROR_RESOURCES)
         {
-            DBG_PRINTF("[BLE TX] FAIL %u retries\r\n", retry_count);
+            if (s_tx_pending)
+            {
+                DBG_PRINTF("[BLE TX] Pending queue busy, dropping new packet\r\n");
+                return;
+            }
+
+            memcpy(s_tx_pending_buf, tx_buffer, total_len);
+            s_tx_pending_len = total_len;
+            s_tx_pending = true;
+            return;
+        }
+        else if (err_code == NRF_ERROR_INVALID_STATE || err_code == NRF_ERROR_NOT_FOUND)
+        {
+            DBG_PRINTF("[BLE TX] Disconnected\r\n");
+            return;
+        }
+        else
+        {
+            DBG_PRINTF("[BLE TX] Err:0x%X\r\n", err_code);
+            return;
         }
     }
 }