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Diffstat (limited to 'doc')
| -rw-r--r-- | doc/references.bib | 8 | ||||
| -rw-r--r-- | doc/report/report.tex | 34 |
2 files changed, 40 insertions, 2 deletions
diff --git a/doc/references.bib b/doc/references.bib index 35cd7d7..a56d059 100644 --- a/doc/references.bib +++ b/doc/references.bib @@ -68,7 +68,7 @@ url = {https://github.com/MicrochipTech/mla_usb}, urlseen = {2025-10-13}, }, -@online{xc8, +@software{xc8, title = {MPLAB\textsuperscript{\textregistered} XC8 Compiler}, organization = {Microchip Technology Inc.}, url = {https://www.microchip.com/en-us/tools-resources/develop/mplab-xc-compilers/xc8}, @@ -211,3 +211,9 @@ organization = {JCLPCB}, url = {https://jlcpcb.com/}, }, +@standard{c99, + organization = {ISO/IEC}, + title = {ISO/IEC 9899:1999}, + subtitle = {Programming Languages --- C}, + year = {1999}, +}, diff --git a/doc/report/report.tex b/doc/report/report.tex index 2702f5b..b209f48 100644 --- a/doc/report/report.tex +++ b/doc/report/report.tex @@ -328,12 +328,44 @@ One may notice that the board sports a USB-B connector: a vestige of the origina The connector is no longer required and will be removed in a future revision. As mentioned above, most of the chosen ICs are available in DIP (through-hole) packages, and were used for prototyping on a breadboard (Fig. \ref{fig:Breadboard}). -They were then transplanted into the PCB once it had been manufactured. +They were then transplanted into the PCB once it had been manufactured (Fig. \ref{fig:PcbAssembled}). This allowed firmware development to be carried out in parallel on the breadboard while waiting for the PCB to arrive (see the timeline in Fig \ref{fig:Timeline}). \section{Firmware} \label{section:Firmware} +Firmware is the program that runs on the board's microcontroller. +It is responsible for interacting with the peripherals, decoding CAN frames, and transforming sensor data into output signal levels to drive the gauges. +It is written in ISO C (C99) \cite{c99}, and it is compiled for the PIC16F1459 using Microchip's XC8 compiler \cite{xc8}. + +The program is divided into a set of C modules. +Each peripheral (MCP2515, 25LC160C, MCP4912) has a corresponding module (\texttt{can}, \texttt{eeprom}, \texttt{dac}). +Collectively, these are known as the HAL (hardware abstraction layer). + +There are also higher-level modules that make use of the HAL. +One example is the \texttt{table} module. +The EEPROM stores several tables that are mappings from sensor-reading-values to output-signal-values. +For example, one table maps engine speed (rpm) to tachometer pulse frequency. +The \texttt{table} module makes use of the \texttt{eeprom} HAL module and provides a simple interface to read and manipulate these mapping tables stored in the EEPROM. + +Dependencies between the modules are shown in Fig. \ref{fig:Dependencies}. + +TODO: module dependency graph. + +The \texttt{main} entrypoint of the firmware simply initializes the HAL and waits to receive an interrupt from the CAN controller or from a timer. +The ISR (interrupt service routine) handles the reception and decoding of CAN frames. +Upon receiving a frame, the ISR decodes the sensor signal contained therein, and looks up the corresponding output signal value in the mapping table. +It then directs one of the peripherals to generate the appropriate output signal accordingly. +For instance, it may instruct one of the DACs to change the voltage being driven to a temperature/pressure gauge, or it may set the period of the tachometer wave. + +The variable-frequency square waves for the tachometer and speedometer are generated using the PIC's built-in timer peripherals. +Upon overflow, the timers trigger the ISR to toggle the apropriate GPIO (general-purpose input/output) pin. +The waves' frequencies are controlled by setting the timers' periods. + + +\subsection*{Calibration} + + TODO |