I've used the nRF8001 on several projects with good success, so I'm generally familiar with the chip's operation. But I'm seeing an issue on a new (custom) board that I'm not sure how to interpret. I wonder if anyone else has seen something similar.
The nRF8001 sends a DeviceStartedEvent after reset that indicates Setup mode, no hardware errors, and two data credits - all perfectly normal. It also accepts any packet sent by the MCU with proper handshaking, sending back a debug byte of 1 and then a stream of zeros during the exchange. Again, perfectly normal.
However, I can't get the chip to actually respond to any packet. Sending the first setup data packet yields no response. I also tried sending a Test packet to put the device in ACI test mode, but that generates no response either.
It's as if the MOSI line were tied to GND, so that the nRF8001 sees only empty ACI packets. But there's no short - I can see the outbound data on the nRF8001's MOSI pin, and setting the MOSI line high does not increase the system's current consumption, as it would if there were some hidden short to ground.
One thing I'm doing differently on this board is putting the 16 MHz crystal on the MCU and feeding the clock signal through to XC1 via an MCU output pin. XC2 is unconnected. I can see the clock running, but there's nothing else on the line - it just runs right from the MCU to XC1. That should be fine, shouldn't it? Is the 16MHz clock even used during basic ACI communication, before the radio is activated?
Another possible issue is that the solder joint on the balun (the matching Johansson chip) looks a bit questionable. Is it possible that a short or open circuit on ANT1 and ANT2 might cause this kind of misbehavior?
At this point, I'm pretty much stuck for other things to try. I'm more or less resigned to rebuilding another copy of the board to rule out some kind of construction issue or hardware defect.
If any of this rings a bell, I'd appreciate any comments.
