Hello,
I have a serial communication application running in my Atmel 89LV52 8052-micro controller.

The communication and the entire application works fine otherwise, but whenever I enable the serial interrupts like this:

IP = 16; // serial = high priority, others = low priority
IE = 128 + 16; // Enable all + serial, THIS LINE SLOWS DOWN THE PERFORMANCE

the performance of the application slows down, but otherwise everything looks OK.

The slow down does not appear in my 8051 simulator, but in a real HW environment it does.

I have tried the code in 2 8052 chips and with 2 boards which makes 4 combinations, and same symptoms in every case.

The system has still worked some time ago, but I don't understand what change has brought this problem.


I initialize the TI and RI like this:
setb _TI ; ti is normally set in this program
clr _RI ; ri is normally cleared


I transmit bytes like this:
void serial_out(unsigned char* str, unsigned char n)
{
while (n != 0)
{
_asm
00001$: jnb ti, 00001$
clr ti
_endasm;
SBUF = *str++;
n--;
}
// finally new line:
_asm
00002$: jnb ti, 00002$
clr ti
mov _SBUF, #0x0d
00003$: jnb ti, 00003$
clr ti
mov _SBUF, #0x0a
_endasm;
}


I receive bytes like this:
void serial_receive_interrupt_handler() interrupt INT_SERIAL _naked
{
_asm
jb ri, 00001$
reti ; no operation when sent a byte, seems to never come here
00001$:
; clr ea
clr es
; storing of the byte into a buffer located into indirect RAM at 0x80 ->
; setb ea
clr ri
setb es
reti
_endasm;
}

It is like serial receive interrupt handler got called continuously. Any help will be appreciated.

- Ari