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Nov 26, 2013, 12:10 AM
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Si1000 secrets

It actually has a way to directly connect a UART to the modulation. The problem is it can't do GFSK in that mode. It also needs a trigger to enter transmit mode. It would be quite involved. The preamble generation & detection would have to be done on the host. Some pins would have to be soldered.

Since the trigger would use the same old slow UART, it would need to buffer as much as the FIFO mode & make any latency advantage a wash. It would allow packets larger than 255 bytes, but that would be more susceptible to errors.

It's not hard wired to do 256 kbits/sec. The data rate can be set to 230400 bits/sec to better synchronize the transmit FIFO with the UART. Si recommends using a register calculator, but they don't provide any obvious register calculator in the wireless development suite. The existing register tables can be interpolated to give values that work for 230400.

The next big win was letting the beacon rate dynamically adapt to the size of the packets. That got the download speed up to 107520 bits/sec with no uploading & a download speed of 65280 bits/sec during a maximum upload speed of 59840 bits/sec. It couldn't be symmetric because it has a minimum beacon rate.

Having a master sending beacons to schedule the packets has remaned a lot faster than cooperatively trying to allocate time slices. The speed limitation may now be entirely the USB adapter, with a custom USB solution getting above 128 kbits/sec. It's still not fast enough for video, but it's almost bearable for static page loads.
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