I have developed a custom board for the RFduino, which provides some I2C based I/O, and uses a CP2103 for the USB/UART. The board seemed to be working fine, allowing me to upload small test applications to the RFduino. However, once I loaded the MPU6050 orientation demo to the board (which incidentally works beautifully), I can no longer program the board. The impression I have is that perhaps some aspect of the high data rate (lots of 115200 baud data), or the short pause after a reset, or some other effect is preventing further programming.
When I attempt to program it, I can see the reset line going low then high, and almost immediately I get the dreaded message
fail........ fail....... fail .......
I wondered if there was some timing diagram that could tell me the timing constraints on the DTR/RESET/Reprogram cycle? (I was wondering if my reset circuitry (which uses a 0.1uF cap, and a 10k pullup) might hold the pin low for too long - I notice that the RFDuino USB board uses a 0.01 uF cap (10000pf) and no pullup. I wondered if the longer low time of my circuit may be causing the issue.
Can someone suggest a possible debugging route for me?