1) there is a problem in atmel mcu using usart and RTS. follow this

Quote:
Do not use the hardware handshaking mode of the USART.
If it is necessary to drive the RTS output high
when the Peripheral DMA receive buffer becomes full,
use the normal mode of the USART.
Configure the Peripheral DMA Controller
to signal an interrupt when the receive buffer is full.
In the interrupt handler code,
write a one to the RTSDIS bit in the USART Control Register (CR).
This will drive the RTS output high.
After the next DMA transfer is started and a receive buffer is available,
write a one to the RTSEN bit in the USART CR so that RTS will be driven low.

remmber to pdca_disable_interrupt_transfer_complete/pdca_enable_interrupt_transfer_complete as needed.

2) in XBEE, mcu RTS-> xbee RTS and mcu CTS-> xbee CTS

3) there is also a problem in XBEE RTS (this was the hard one), after RTS is set there is an over head of 6 byte that will pass (if they where in XBEE RX buffer)
so add “overhead” byte to each transmition
in matlab code

s = serial(port,’BaudRate’,baudrate,’DataBits’,dataBits,’Parity’,parity,’StopBits’,stopbits);
data=[ 'some data'];
overhead=[ 0 1 2 3 4 5];

% open serial
fopen(s);
fwrite(s,[ data overhead 1 2 3 4 overhead 5 6 overhead] ,’uint8′);
fclose(s);

this will do the trick

4) as overhead is needed, the MCU RXCHR register will be full
remmber to empty it before next pdca buffer reloading.
if not the last overhead byte will be read

if (usart_test_hit(TEMP_USART))
junk=(TEMP_USART->rhr & AVR32_USART_RHR_RXCHR_MASK) >> AVR32_USART_RHR_RXCHR_OFFSET;

5) this is my interupt function

/*! \USART brief RTS setting
*/
#if __GNUC__
__attribute__((naked))
#elif __ICCAVR32__
#pragma shadow_registers = full // Naked.
#endif
static void pdca_RTS_int_handler( void)
{
/* This ISR can cause a context switch, so the first statement must be a
call to the portENTER_SWITCHING_ISR() macro. This must be BEFORE any
variable declarations. */
portENTER_SWITCHING_ISR();

// prevent re-entering
pdca_disable_interrupt_transfer_complete( PDCA_CHANNEL_RX);

// close !(RTS), stop transfer
TEMP_USART->cr = AVR32_USART_CR_RTSDIS_MASK;

portEXIT_SWITCHING_ISR();
#endif
}

6) this is my reading code

// clean last overhead
if (usart_test_hit(TEMP_USART))
junk=(ZIGBEE_USART->rhr & AVR32_USART_RHR_RXCHR_MASK) >> AVR32_USART_RHR_RXCHR_OFFSET;
// load channel
pdca_reload_channel( PDCA_CHANNEL_RX, (void *) psParametersShadow, sizeof(xParameters));

// Enable PDCA transfer interrupt when completed
pdca_enable_interrupt_transfer_complete( PDCA_CHANNEL_RX);

//set !(RTS), start transfer
TEMP_USART->cr = AVR32_USART_CR_RTSEN_MASK;

// wait read end
while(!(pdca_get_transfer_status(PDCA_CHANNEL_RX) & PDCA_TRANSFER_COMPLETE));

hope this will help someone

do you think that i can solve this using api mode ?

thanks,