[fix] fix flash_download when first byte is not 0x55 in shakehand

tools/flash_download.py

@@ -67,8 +67,8 @@ class FlashDownloader:
         # time.sleep(0.5)       # 等待500ms
         print("Pre-erase signals set")
         shakehand = self.ser.read(4)
-        print("shakehand=", shakehand)
-        return shakehand == b'\x55\x55\x55\x55'
+        print("shakehand=", shakehand.hex(' ').upper())
+        return len(shakehand) == 4 and shakehand[3] == 0x55
 
     def control_signals_post_download(self):
         """下载完成后的信号控制"""
@@ -76,7 +76,7 @@ class FlashDownloader:
         self.ser.rts = True   # RTS拉低
         self.ser.dtr = True   # DTR拉低
         time.sleep(0.1)       # 等待100ms
-        self.ser.rts = False  # RTS拉高
+        # self.ser.rts = False  # RTS拉高
         print("Post-download signals set")
 
     def calculate_checksum(self, data):
@@ -243,6 +243,9 @@ class FlashDownloader:
             print("shake hands failed")
             sys.exit(1)
 
+        # 清除 RX Buffer
+        self.ser.reset_input_buffer()
+
         # 擦除Flash (擦除足够的空间)
         erase_size = ((len(file_data) + 4095) // 4096) * 4096  # 假设擦除块大小为4KB
         if not self.erase_flash(self.address, erase_size):