Controlling a 8051 microcontroller through bluetooth

I realize that you're looking for an 8051, but I think that's an antiquated choice. For an old, trusty tool, 8051's are great, but I'd strongly recommend against starting there. They're widely used in industry because they're incumbent, not because they're the best.

The easiest way to start is the Arduino-- it's cheap and easy to program. You can program it with a subset of C/C++, at least to start with.

If that seems not hardcore enough, and PICs are ruled out, I'd start with an MSP430 from Texas Instruments. Digikey has an eval board with two different MSP430s for $100. You also need a JTAG programmer. You can get the TI FET, but I've had success with the cheaper Softbaugh programmer.

(But if you really are dying for an 8051, I'd start with an Atmel chip and the Keil tools.)

How do you get the characters from the serial port buffer register? If you simply read them in a loop like

void main() {       
  char c;
  while (1) {
    c=SBUF;
    do_something(c);
  }
}

Then you will miss characters once the execution time of do_something() gets longer. Note that this includes time spend in intterrupts. The 8051 serial port has no hardware fifos, a character will be overwritten by the next one if it was not read in time.

Our solution was to read the characters into a Ringbuffer during the serial Intterupt, and to use the FIFO in the main loop. Works (with high priority interrupt) for 460800 Baud with 7,3728 MHz crystal on a Silabs 80C51FXXX.

Update

As we now see the source coude, the bug is now clear: You wait in the main loop for your character to be sent. But that means you wait a whole "character time" without being able to read your interrupt character buffer, and another few cyles to detect and read the next. This is too long if the sender sends characters fast, as a PC does.