diff options
| -rw-r--r-- | doc/references.bib | 19 | ||||
| -rw-r--r-- | doc/report/report.tex | 40 |
2 files changed, 47 insertions, 12 deletions
diff --git a/doc/references.bib b/doc/references.bib index 8653bed..0ae9d5c 100644 --- a/doc/references.bib +++ b/doc/references.bib @@ -236,7 +236,7 @@ @software{BitTimingScript, author = {Sam Anthony}, title = {CAN bit timing configuration script}, - url = {http://git.samanthony.xyz/can-gauge-interface.git/tree/sw/bittiming/bittiming.py?id=5e6a57011bdaf23e012eac28c04de3ebcbe65f9e}, + url = {http://git.samanthony.xyz/can-gauge-interface.git/tree/sw/bittiming/bittiming.py}, }, @online{CanBitrates, title = {CAN FAQ}, @@ -244,3 +244,20 @@ orgnanization = {CAN-bus Wiki Project}, url = {http://www.can-wiki.info/doku.php?id=can_faq:can_bitrates}, }, +@online{SocketCan, + title = {SocketCAN --- Controller Area Network}, + author = {The kernel development community}, + organization = {The Linux Kernel}, + url = {https://docs.kernel.org/networking/can.html}, +}, +@software{Cal, + author = {Sam Anthony}, + title = {Cal}, + subtitle = {Calibration Software for the Analog Gauge Driver with CAN Interface}, + url = {http://git.samanthony.xyz/can-gauge-interface.git/tree/sw/cal}, +}, +@online{Golang, + title = {The Go Programming Language}, + organization = {The Go Authors}, + url = {https://go.dev/}, +}, diff --git a/doc/report/report.tex b/doc/report/report.tex index 5759605..fe85a44 100644 --- a/doc/report/report.tex +++ b/doc/report/report.tex @@ -196,7 +196,7 @@ Each of these topics are covered in the subsequent sections. The hardware is a PCB (printed circuit board) hosting a set of ICs (integrated circuits)---as listed in the previous section (Fig \ref{fig:BlockDiagram})---and some supporting passive components: resistors, capacitors, and an inductor. -\subsection*{Component selection} \label{subsection:ComponentSelection} +\subsection{Component selection} \label{subsection:ComponentSelection} A car is a harsh environment. The device is subject to vibration, EMI (electromagnetic interference), and large variations in temperature. @@ -247,7 +247,7 @@ Thus, an 8-bit DAC with 256 steps would have been insufficient, and so a 10-bit The MCP4912 is a dual-channel 10-bit DAC, so two of them are required to drive the board's four analog outputs. -\subsection*{Power supply} +\subsection{Power supply} Standard automotive electrical systems operate at a nominal voltage of around 13.7V, but can swing between 9 and 16V. The voltage supply often has a strong pulsating component as well, known as ripple. @@ -280,7 +280,7 @@ Unfortunately, the passive component values were calulated incorrectly, which re This mistake is discussed further in \S\ref{section:Testing}. -\subsection*{PCB design and manufacture} \label{subsection:PcbDesign} +\subsection{PCB design and manufacture} \label{subsection:PcbDesign} The schematic (Fig. \ref{fig:Schematic}) and PCB (Figs. \ref{fig:PcbPours}, \ref{fig:Pcb3d}, and \ref{fig:PcbAssembled}) were designed in KiCad \cite{kicad}. JCLPCB manufactured the board \cite{jlcpcb}. @@ -370,7 +370,7 @@ Upon overflow, the timers trigger the ISR to toggle the apropriate GPIO (general The waves' frequencies are controlled by setting the timers' periods. -\subsection*{Calibration} +\subsection{Calibration} \label{subsection:FwCalibration} In order for the device to work with any combination of sensors, gauges, and CAN encoding schemes, it must be configurable by the end-user. @@ -400,9 +400,32 @@ In addition to the firmware, several other pieces of software were developed ove In contrast with the firmware which runs on the device's microcontroller, these programs target a personal computer. -\subsection*{CAN bit timing calculation} +\subsection{Calibration software} \label{subsection:SwCalibration} -The first program is a small Python script for calculating CAN bit timing parameters. +As described above, the user-calibration, stored in the board's EEPROM, allows the device to be configured for any combination of sensors, gauges, and CAN encoding schemes. + +The \emph{cal} program flashes the calibration from a personal computer onto the device via the CAN bus \cite{Cal}. +Cal takes a set of files containing the user-calibration as input, and outputs CAN frames that are sent to the device. +These are the special \emph{control} frames mentioned in \S\ref{subsection:FwCalibration} and defined fully in \cite{calfmt}. + +The calibration is defined by a DBC file \cite{dbc10} and a set of CSV files. +The DBC file specifies the CAN encoding scheme which describes how sensor readings, represented as \emph{signals} in the DBC file, are encoded into CAN frames. +The DBC file can specify one signal for each gauge, e.g., \texttt{EngineSpeed} for the tachometer, \texttt{EngineOilPressure} for one of the analog gauges, and so on. +This allows the device to be configured for the CAN encoding scheme that the car's EMS uses. + +The CSV files define the tables which map sensor-reading-values to output-signal-values which drive the gauges. +There is one table, and thus one CSV file, for each signal. +This allows the device to be configured for the particular sensors and gauges installed in the car. + +Cal is written in 674 lines of Go \cite{Golang}. +It uses the Linux kernel's SocketCAN \cite{SocketCan} facility to access the CAN bus. +Thus, its support is limited to Linux. +Ideally it should be ported to other operating systems in the future. + + +\subsection{CAN bit timing calculation} \label{subsection:Bittiming} + +The second program is a small Python script for calculating CAN bit timing parameters. Each node in a CAN network has its own clock generator. The bit timing parameters can be configured individually at each node in order to achieve a common bit rate throughout the network even though the nodes' clock periods may be slightly out of sync. @@ -421,11 +444,6 @@ Therefore, although the MCP2515 supports bitrates up to 1Mbps, the board is limi This can be remedied in a future revision by adding a dedicated 20MHz oscillator for the CAN controller. -\subsection*{Calibration software} - -TODO - - \section{Testing} \label{section:Testing} TODO |