include "mbed.h"

I2CSlave slave(PB_9, PB_8);

int main() {
   char buf[10];
   char msg[] = "Slave!";

   slave.address(0x0A);
   while (1) {
       int i = slave.receive();
       switch (i) {
           case I2CSlave::ReadAddressed:
               slave.write(msg, strlen(msg) + 1); // Includes null char
               break;
           case I2CSlave::WriteGeneral:
               slave.read(buf, 10);
               printf("Read G: %s\n", buf);
               break;
           case I2CSlave::WriteAddressed:
               slave.read(buf, 10);
               printf("Read A: %s\n", buf);
               break;
       }
       for(int i = 0; i < 10; i++) buf[i] = 0;    // Clear buffer
   }
}

I am having a problem using NUCLEO-F401RE board for testing the i2c slave. I was using the mbed OS 5 i2c slave example (https://docs.mbed.com/docs/mbed-os-api-reference/en/5.1/APIs/interfaces/digital/I2CSlave/) with the bit rate standard 100K bit/s. I used the Total Phase Aardvark I2C host adapter sending bytes (8 bytes) to NUCLEO-F401RE board. The NUCLEO-F401RE i2c slave always holds down the SCL line forever in middle of the data transfer, which can be viewed clearly by a oscilloscope or a I2C protocol analyzer. Please help! The following is the test code: <<code title=I2C {{/media/uploads/jingxizhang/img_20160821_173429772.jpg}} Slave test>> include "mbed.h" I2CSlave slave(PB_9, PB_8); int main() { char buf[10]; char msg[] = "Slave!"; slave.address(0x0A); while (1) { int i = slave.receive(); switch (i) { case I2CSlave::ReadAddressed: slave.write(msg, strlen(msg) + 1); // Includes null char break; case I2CSlave::WriteGeneral: slave.read(buf, 10); printf("Read G: %s\n", buf); break; case I2CSlave::WriteAddressed: slave.read(buf, 10); printf("Read A: %s\n", buf); break; } for(int i = 0; i < 10; i++) buf[i] = 0; // Clear buffer } } <</code>>