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97 lines
2.4 KiB
97 lines
2.4 KiB
\section{USART Unit}
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The \gls{USART} unit provides access to one of the microcontroller's \gls{USART} peripherals. See \cref{sec:theory-usart} for more information about the interface.
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Most \gls{USART} parameters available in the hardware peripheral's configuration registers can be adjusted to match the application's needs. The peripheral is capable of driving RS-485 transceivers, using the \gls{DE} output for switching between reception and transmission.
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The unit implements asynchronous reception and transmission with \gls{DMA} and a circular buffer. Received data is sent to the host in asynchronous events when a half of the buffer is filled, or after a fixed timeout from the last received byte. The write access is, likewise, implemented using \gls{DMA}.
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\todo[inline]{add a diagram of the dma-based reception}
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\subsection{USART Configuration}
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\begin{inicode}
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[USART:ser@6]
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# Peripheral number (UARTx 1-4)
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device=1
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# Pin mappings (TX,RX,CK,CTS,RTS/DE)
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# USART1: (0) A9,A10,A8,A11,A12 (1) B6,B7,A8,A11,A12
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# USART2: (0) A2,A3,A4,A0,A1 (1) A14,A15,A4,A0,A1
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# USART3: (0) B10,B11,B12,B13,B14
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# USART4: (0) A0,A1,C12,B7,A15 (1) C10,C11,C12,B7,A15
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remap=0
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# Baud rate in bps (eg. 9600)
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baud-rate=115200
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# Parity type (NONE, ODD, EVEN)
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parity=NONE
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# Number of stop bits (0.5, 1, 1.5, 2)
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stop-bits=1
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# Bit order (LSB or MSB first)
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first-bit=LSB
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# Word width (7,8,9) - including parity bit if used
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word-width=8
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# Enabled lines (RX,TX,RXTX)
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direction=RXTX
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# Hardware flow control (NONE, RTS, CTS, FULL)
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hw-flow-control=NONE
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# Generate serial clock (Y,N)
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clock-output=N
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# Clock polarity: 0,1
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cpol=0
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# Clock phase: 0,1
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cpha=0
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# Generate RS485 Driver Enable signal (Y,N) - uses RTS pin
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de-output=N
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# DE active level: 0,1
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de-polarity=1
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# DE assert time (0-31)
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de-assert-time=8
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# DE clear time (0-31)
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de-clear-time=8
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\end{inicode}
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\subsection{USART Events}
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\begin{cmdlist}
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0 & \cname{DATA\_RECEIVED}
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Data was received on the serial port.
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&
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\begin{cmdpld}
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\cfield{u8[]} received bytes
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\end{cmdpld} \\
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\end{cmdlist}
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\subsection{USART Commands}
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\begin{cmdlist}
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0 & \cname{WRITE}
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Add data to the transmit buffer. Sending is asynchronous, but the command may wait for free space in the \gls{DMA} buffer.
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& \begin{cmdreq}
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\cfield{u8[]} bytes to write
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\end{cmdreq} \\
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1 & \cname{WRITE\_SYNC}
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Add data to the transmit buffer and wait for the transmission to complete.
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& \begin{cmdreq}
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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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