You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
101 lines
2.7 KiB
101 lines
2.7 KiB
\section{USART Unit}
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
The unit implements asynchronous reception and transmission with \gls{DMA} and a circular buffer (\cref{fig:uart_rx_dma}). 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 a \gls{DMA} buffer.
|
|
|
|
\begin{figure}[h]
|
|
\centering
|
|
\includegraphics[scale=1]{img/uart-dma.pdf}
|
|
\caption{\label{fig:uart_rx_dma}Principle of DMA-based UART reception. Interrupt is generated in the half and at the end of the buffer, at which point the write pointer wraps back to the beginning.}
|
|
\end{figure}
|
|
|
|
\subsection{USART Configuration}
|
|
|
|
\begin{inicode}
|
|
[USART:ser@6]
|
|
# Peripheral number (UARTx 1-4)
|
|
device=1
|
|
# Pin mappings (TX,RX,CK,CTS,RTS/DE)
|
|
# USART1: (0) A9,A10,A8,A11,A12 (1) B6,B7,A8,A11,A12
|
|
# USART2: (0) A2,A3,A4,A0,A1 (1) A14,A15,A4,A0,A1
|
|
# USART3: (0) B10,B11,B12,B13,B14
|
|
# USART4: (0) A0,A1,C12,B7,A15 (1) C10,C11,C12,B7,A15
|
|
remap=0
|
|
|
|
# Baud rate in bps (eg. 9600)
|
|
baud-rate=115200
|
|
# Parity type (NONE, ODD, EVEN)
|
|
parity=NONE
|
|
# Number of stop bits (0.5, 1, 1.5, 2)
|
|
stop-bits=1
|
|
# Bit order (LSB or MSB first)
|
|
first-bit=LSB
|
|
# Word width (7,8,9) - including parity bit if used
|
|
word-width=8
|
|
# Enabled lines (RX,TX,RXTX)
|
|
direction=RXTX
|
|
# Hardware flow control (NONE, RTS, CTS, FULL)
|
|
hw-flow-control=NONE
|
|
|
|
# Generate serial clock (Y,N)
|
|
clock-output=N
|
|
# Clock polarity: 0,1
|
|
cpol=0
|
|
# Clock phase: 0,1
|
|
cpha=0
|
|
|
|
# Generate RS485 Driver Enable signal (Y,N) - uses RTS pin
|
|
de-output=N
|
|
# DE active level: 0,1
|
|
de-polarity=1
|
|
# DE assert time (0-31)
|
|
de-assert-time=8
|
|
# DE clear time (0-31)
|
|
de-clear-time=8
|
|
\end{inicode}
|
|
|
|
|
|
\subsection{USART Events}
|
|
|
|
\begin{cmdlist}
|
|
|
|
0 & \cname{DATA\_RECEIVED}
|
|
Data was received on the serial port.
|
|
&
|
|
\begin{cmdpld}
|
|
\cfield{u8[]} received bytes
|
|
\end{cmdpld} \\
|
|
|
|
\end{cmdlist}
|
|
|
|
|
|
\subsection{USART Commands}
|
|
|
|
\begin{cmdlist}
|
|
|
|
0 & \cname{WRITE}
|
|
Add data to the transmit buffer. Sending is asynchronous, but the command may wait for free space in the \gls{DMA} buffer.
|
|
& \begin{cmdreq}
|
|
\cfield{u8[]} bytes to write
|
|
\end{cmdreq} \\
|
|
|
|
1 & \cname{WRITE\_SYNC}
|
|
Add data to the transmit buffer and wait for the transmission to complete.
|
|
& \begin{cmdreq}
|
|
\cfield{u8[]} bytes to write
|
|
\end{cmdreq} \\
|
|
|
|
\end{cmdlist}
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|