Could you please upload the complete code here?

I could not see where you have define:

  //mcu_clock_setup();
  //mcu_reset_setup();

I also could not see how you configure the UART1, how you configure the peripheral to generate target baud rate?

1 EFM8LB1_UART0_Interrupt.

2 EFM8LB1_UART1_Lib_Autobaud_Buffer

demo can not work

How you determine that EFM8LB1_UART0_Interrupt can not work?

on my side it works fine.

and  EFM8LB1_UART_Lib_Buffer ,which can only work at br 115200,when I modified the code to set another br value，it can not work well.

the CDC UART (VCOM) only support 115200. I think that is the reason you see the failure.

https://www.silabs.com/community/mcu/8-bit/knowledge-base.entry.html/2016/07/18/no_effect_to_change-en32

For the c8051F320

How would i determine how long it takes to complete an instruction?

for the below function i can pass an unsigned char "count" so i can adjust the delay ….so lets say I pass 1 how long would it take to complete in ms both for loops especially the second where j exceeds 112 and exits the for loop ?
 

void delay(unsigned int count)  
{
 int i,j;
 for(i=0;i<count;i++)
 for(j=0;j<112;j++);
}

AFAIK, this is hardware controlled internally and there is no software solution.

AFAIK, this is hardware controlled internally and there is no software solution.

You could get the clock cycle for each instruction in table 9.1 of the datasheet.

The delay for the code you quote here may have relation to some factors like optimization level. 

You may take a look at the disassembly code to see the instruction and estimate the delay.

What do you mean by "in simulator mode in  simplicity studio"?

If you are trying to simulate to run code without a device connected, I don't think that (all features) was supported.

AFAIK, there is no replacement for the CP2120.

You may consider to use Silabs 8-bit MCU and develop the firmware by your own.

To get answer to question on device Si32185, you may consider to create a support case.

http://www.silabs.com/support/Pages/default.aspx

To get answer to question on device Si32185, you may consider to create a support case.

http://www.silabs.com/support/Pages/default.aspx