part 5

Errata
during writing the code some important errata where found
in board when MQ7 sensor is continuous running on 5v
and at the avr32 and the XBee processors



avr32 MCU:

1. 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.
2. CTS can only be used by the Peripheral DMA Controller in hardware mode and RTS can be used by workaround in non hardware mode. DMA Controller for TX should first wait that the DMA Controller for RX will finish reading and then configuring the Peripheral DMA Controller to hardware mode at the MR register after that transmit can start by pointing to the transmitting buffer. when transmitting is finished MR register should be changed to non hardware mode by signal an interrupt when the transmit buffer is empty and disable hardware mode in the MR register DMA Controller for RX should wait that the DMA Controller for TX will finish writing and then it can work safe in non hardware mode

XBee:
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


MQ7:

needs to cycle 5v for 60 seconds, then 1.4V for 90 seconds and so on.

this is not supported in this version, the sensor is continuous running on 5v. 

no solution to that in this version.