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65 lines
2.0 KiB
65 lines
2.0 KiB
\section{SPI Unit}
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The \gls{SPI} unit provides access to one of the microcontroller's \gls{SPI} peripherals. It can be configured to use any of the different speeds, clock polarity and phase settings available in its control registers.
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The unit handles up to 16 slave select (\gls{NSS}) signals and supports message multi-cast (addressing more than one slaves at once). Protection resistors should be used if a multi-cast transaction is issued with \gls{MISO} connected.
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The QUERY command of this unit, illustrated by figure \ref{fig:spi_query}, is flexible enough to support all types of \gls{SPI} transactions: read-only, write-only, and read-write with different request and response lengths. The slave select pin is held low during the entire transaction.
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\begin{figure}[h]
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\centering
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\includegraphics[scale=1.1] {img/spi-query.pdf}
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\caption{\label{fig:spi_query}SPI transaction using the QUERY command}
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\end{figure}
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\subsection{SPI Configuration}
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\begin{inicode}
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[SPI:spi@5]
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# Peripheral number (SPIx)
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device=1
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# Pin mappings (SCK,MISO,MOSI)
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# SPI1: (0) A5,A6,A7 (1) B3,B4,B5
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# SPI2: (0) B13,B14,B15
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remap=0
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# Prescaller: 2,4,8,...,256
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prescaller=64
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# Clock polarity: 0,1 (clock idle level)
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cpol=0
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# Clock phase: 0,1 (active edge, 0-first, 1-second)
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cpha=0
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# Transmit only, disable MISO
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tx-only=N
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# Bit order (LSB or MSB first)
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first-bit=MSB
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# SS port name
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port=A
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# SS pins (comma separated, supports ranges)
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pins=0
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\end{inicode}
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\subsection{SPI Commands}
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\begin{cmdlist}
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0 & \cname{QUERY}
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Exchange bytes with a slave device
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& \begin{cmdreq}
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\cfield{u8} slave number 0--16
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\cfield{u16} response padding
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\cfield{u16} response length
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\cfield{u8[]} bytes to write
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\end{cmdreq}
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\cjoin
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\begin{cmdresp}
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\cfield{u8[]} received bytes
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\end{cmdresp} \\
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1 & \cname{MULTICAST}
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Send a message to multiple slaves at once. The address is a bit map (e.g. 0x8002 = slaves 1 and 15).
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& \begin{cmdreq}
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\cfield{u16} addressed slaves
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\cfield{u8[]} bytes to write
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\end{cmdreq} \\
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\end{cmdlist}
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