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Decoding Data Streams with a SPI Disclosure Number: IPCOM000197208D
Publication Date: 2010-Jun-28
Document File: 1 page(s) / 9K

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Decoding Data Streams with a SPI

Decoding data streams with a SPI is normally done between two devices that share a SPI interface, that interface may be implemented either in hardware or software. This concept uses half of a normal SPI interface to send/receive a data stream to a device that is not designed for SPI data streams, specifically, devices that cannot handle the SPI handshaking or clocking mechanisms. In this concept, the SPI device is used to decode a stream of data from a radio receiver.

Because the SPI interface requires some level of handshaking, measures must be take to "provide handshaking" for the non-SPI device, in this case, the radio receiver. For example, normal SPI transactions synchronize data using a clock signal that is shared between the SPI devices. This results in a bit per clock cycle. In this concept, because the clock source is maintained separately, more than one cycle (oversampling) per bit may be done.

During decoding a timer in the microprocessor is used to clock the SPI at a multiple of the data bit rate in order to oversample each bit of data received from the radio. The microprocessor DMA is employed to transfer the oversampled data into a buffer in memory where post processing can be employed to convert the oversampled data stream into normalized data. During encoding a timer in the microprocessor is used to clock the SPI at the normal data rate, the DMA is used to transfer the data from memory to the SPI where it is sent t...