SPI hardware and software testing notes

Now I have assembled the signal cables based on RPi headers P1 and P5, and connected to GPi through the signal routing board with test LED, buzzer,and button.

I used gz_test to verify that all connections are more or less OK.  This also make sure the SPI and RPCLK0 signals are properly connected to the signal board, then Guzunty Pi.

Before playing with GPi, I only have limited experience in SPI, and I only rely on RFM12B's frequency setting feature to make sure that the SPI hardware and software is working OK.  Now that I have GPi, I can forget about RFM12B.

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