The problem that Serial.available continuously returned -1 was not resolved.

[tistructor]

I'm using your core version 1.0.6 but the problem that Serial.available continuously returned -1 hasn't been solved.

[tistructor]

I found the problem.

#if defined(CH32V003) || defined(CH32V203) || defined(CH32X035) || defined(CH32V103) || defined(CH32V307)
#define ENABLE_RX_BUFFER 1
#else
#define ENABLE_RX_BUFFER 0
#endif
ENABLE_RX_BUFFER was not enabled.

I added
defined(CH32V00x) || defined(CH32V003F4)

in both the HardwareSerial.h and HardwareSerial.cpp files

Now the Serial.available function works correctly.

The chip is not correctly identified when the build is made.