开机连接WiFi，使用bl远程升级，ymodem_ota没问题，但是使用httpota就有问题。难道是esp32接收数据长度不行，具体现象如下：
使用中的ymodem_ota可以正常使用，升级成功。
现象如

msh />y
ymodem_ota
msh />ymodem_ota
Default save firmware on download partition.
Warning: Ymodem has started! This operator will not recovery.
Please select the ota firmware file and use Ymodem to send.
CC
开始 ymodem 传输。  按 Ctrl+C 取消。
  100%     103 KB    2 KB/s 00:00:42       0 Errors
Download firmware to flash success.
System now will restart...
XXXXXXXXXXXXXXXXXXXXXXX
XX
XX
XX
XXXXXXXXXXXXXXXXX
</p>

接着遇到这个问题
http file_size:105488 [I/http_ota] Start erase flash (download) partition! [I/http_ota] Erase flash (download) partition success! [I/http_ota] OTA file size is (105488) [E/at.clnt] read line failed. The line data length is[W/UART] Warning: There is no enough buffer for saving data, please increase the RT_SERIAL_RB_BUFSZ option. ving data, please increase [E/at.clnt] read line failed. The line data length is out of buffer size(1024)! [E/at.clnt] read line failed. The line data length is out of buffer size(1024)! [E/at.clnt] read line failed. The line data length is out of buffer size(1024)! [E/at.clnt] read line failed. The line data length is out of buffer size(1024)! [E/at.clnt] read line failed. The line data length is out of buffer size(1024)!

解决办法好像是：

```#define ESP32_SAMPLE_RECV_BUFF_LEN 2048

define PKG_USING_AT_DEVICE_V202

define PKG_AT_DEVICE_VER_NUM 0x20002```

然后又遇见一直老是下载在85%停止，似乎到多人都遇到过这个问题：
[D/web] get position handle response(200). http file_size:78960 [I/http_ota] Start erase flash (download) partition! [I/http_ota] Erase flash (download) partition success! [I/http_ota] Download: [====================================================================================> ] 84% [E/at.skt] AT socket (0) receive timeout (6000)! [I/http_ota] Download: [=====================================================================================> ] 85%

改了要些地方不行，这个问题解决是看了：《HTTP-OTA下载固件失败！》https://www.rt-thread.org/qa/forum.php?mod=viewthread&tid=11958&highlight=ota
解决的。