Android UsbSerial with esp8266/ch340. (bootloader mode)

Hello Guys Please bid if you are android developer, and have esp8266/ch340, have serial communication experience. Please bid with "I have esp8266, android phone" I am trying to convert the open source python project [login to view URL] to Android(java) project. In android, for serial communication, I am using Usb Serial library. I need only esp8266 feature from [login to view URL], so I only converted the esp8266 function. From UsbSerial library, I am using synchronous api, because the [login to view URL] use synchronous command for Serial read/write. Current project is working well with esp8266/FTDI, esp8266/cp2102 same as esptool.py. My problem is not working with esp8266/ch340. Of course, the [login to view URL] is working well with esp8266/ch340. But, my android project is not working with it. In android, the main command which used in [login to view URL] is setDTR, setRTS, serial Read and serial Write. Each command working well although in esp8266/ch340 in normal mode(not bootloader mode) . Also, I confirmed the esp8266 can be bootloader mode correctly via combination of setDTR, setRTS. More correctly confirm bootloader mode, I can use Flash button and RST button of esp8266. [login to view URL] With esp8266/ch340, I cannot pass the first step with android project. The first step is sync operation. From android, call write command with [login to view URL], then the esp8266 is response as bytes. Main problem is cannot read response command from esp8266. From UsbSerial, there is syncRead, syncWrite commands, also there is asynchronous command for serial operation. The [login to view URL] is made with synchronous api, So, I am using synchronous api in android project. Also, current project is perfect with esp8266/FTDI, esp8266/cp2102. So, I think, the main algorithm is successfully converted from [login to view URL] But, esp8266/ch340, current project is not working. From debug, I confirmed cannot read any bytes from esp8266/ch340 in bootloader mode. For debug, I created new project using asynchronous api. With using button of esp8266, make esp8266/ch340 bootloader mode, I am writing the sync command to esp8266. [login to view URL] flash button, rst button From [login to view URL], the esp8266 is send response command, but cannot read response in esp8266/ch340. But, I found strange things. After bootloader mode, write sync command, and disconnect the usb from android, then, I can see the correct response command in Disconnecting moment. If I write sync command 3 times, then the 3 response command is arrived at disconnecting moment. How I can solve this problem? How I can debug esp8266 in bootloader mode? From debugging, this is main problem in esp8266/ch340(bootloader mode).