Warning 15: MULTIPLE CALL TO FUNCTION

"I believe that function PutMultiChar_SCI() is not called by Int0_ISR(), although it was." (my emphasis)

Well, if it was called that'll be the reason!

Note that the warning doesn't mean that there's a direct call from int0_isr - just that there's a call somewhere in the call tree from int0_isr.
eg, is it called by something like printf...?

"I believe that function PutMultiChar_SCI() is not called by Int0_ISR(), although it was." (my emphasis)

Well, if it was called that'll be the reason!

Note that the warning doesn't mean that there's a direct call from int0_isr - just that there's a call somewhere in the call tree from int0_isr.
eg, is it called by something like printf...?

Thanks for response.

After sent the initial post, I double check the *.map file which includes function call tree and try to find any link between PutMultiChar_SCI() with Int0_ISR() function.

There are some facts listed below
(1) PutMultiChar_SCI() is called at multiply places within the main loop, but not Int0_ISR().

(2) I can remove L15 warning by make PutMultiChar_SCI() reentrant, but this does not make any sense for me, because I have no RTOS only main loop and interrupt service routine.

(3) I never use printf() since I found it is longer than 700 lines in VC++, I prefer to use such as small convertion library. Thanks.

"I never use printf()"

I never said that you did - I said, "something like printf"

Are you sure that you don't have any other functions that get called in your ISR, and end up calling something that calls PutMultiChar_SCI()
There must be something - or the linker wouldn't complain!

"I can remove L15 warning by make PutMultiChar_SCI() reentrant"

Of course - the reason the Linker has this warning is that C51 functions are inherently not reentrant!

"this does not make any sense for me, because I have no RTOS only main loop and interrupt service routine."

The problem is that C51 functions are inherently not reentrant - it makes no difference whether the reentrant calls are due to an RTOS or due to a Main loop and ISRs

"I can remove L15 warning by make PutMultiChar_SCI() reentrant"
and end up with a true mess.

If you have ANYTHING that get called both by main (and subs thereof) and an ISR (and subs thereof) you will likey "install" a time bomb.

remove ALL function call from the ISR (there should be none anyhow) and then see what the linker tell you.

Erik