[avr-chat] Problems sending byte to ATmega128 via USART0 when MCU is streaming bytes out.

[Rick Mann]

I suspect this is not an AVR problem, but rather an issue between my  
Mac OS X machine and the bluetooth module I'm using with my  
ATmega128. Nevertheless, I'm hoping someone can shed some light on  
the problem.

I have a BlueSMiRF bluetooth serial module. It's got TTL serial that  
connects to the '128, and then it establishes a bluetooth connection  
to my PowerBook, were it shows up under /dev/tty.Foo.

I'm able to send data to it, and get data back, no problem. The  
module has RTS/CTS flow control, but I'm never saturating the link  
such that its buffers fill and RTS gets asserted.

The problem I'm running into is this. If the mega128 sends data at  
rate of 7 bytes every 1/200th of a second, at 76800 baud, and I  
attempt to send a single byte from the PowerBook to the BT module,  
that byte never seems to show up. I'm watching on the 'scope to make  
sure RTS/CTS stay asserted, and also looking for traffic on TX and  
RX. I can see the traffic being sent to the PowerBook, but that byte  
from the PowerBook to the BT module's MCU output never shows up.

If I stop execution in GDB, which stops the transmission of bytes,  
suddenly that sent byte appears. I guess I've just convinced myself  
that the BT module is acting in a half-duplex way, buffering incoming  
data until outgoing stops. This kinda sucks.

Does anyone have any suggestions? It's not like there aren't breaks  
in the transmitted data...

TIA

--
Rick