Embien has carved itself a niche in the automotive industry serving customers creating various products such as instrument clusters, infotainment systems, telematics control units, telematic gateway units, motor control units, key fob, TPMS receivers, etc. One of our silicon partners recommended our services in developing an instrument cluster for an electric tractor to a Tier 1. This case study explains the challenges associated with the design along with how Embien overcame them and helped the customer realize their product vision.
The electric tractor instrument cluster came with the typical set of any automotive product – low cost, faster time to SoP (start of production) and not so well-defined requirements. Technically, the cluster had to include 2 stepper motor-based gauges (one for RPM and another for Speed) whose response had to be smooth and to have the ability for zero-point detection (ZPD). With rich experience in developing such clusters, Embien was able to assemble an expert design team and kick started the development.
Based on our experience, we could come up with the high-level architecture block diagram of the electric tractor instrument cluster very quickly. To clear out ambiguities later, our team specified the System Requirement Specification (SRS) document with all the necessary requirements. With thorough review from our customer and their end-customer, it was finalized. Then the hardware team and software team started their high-level design document (HDD) which was once again approved by our customer.
Our embedded hardware design team identified Renesas RL78 MCU as the heart of the system. With rich peripheral set, RL78 could offer necessary interfaces for the cluster like CAN connectivity, 2 stepper motor-based gauge control, pulse inputs, PWM outputs, I2C for EEPROM¸RTC etc. All the components were chosen from the preferred list of the customer, so that it is optimized for their production line. To keep the cost low, a 2-layer design was finalized. The form factor was matched with enclosure design by closely collaborating with their mechanical design team.
Our embedded software team, in the meantime, started working on the RL78 evaluation kits and developed the firmware with the Renesas CS+ development environment. With the support of Renesas applet configuration tool, all the underlying Hardware Abstraction Layer (HAL) interfaces are brought up quickly and validated. External peripheral like EEPROM, etc. are added using a break-out board and drivers brought up.
To support the in-vehicle networking, Flint System Configurator and RAPDISEA IVN stack were utilized. With the DBC file available for all the messages in the system, it was input to the Flint and corresponding configuration file generated with mapping the data variables. This configuration settings were provided to the RAPIDSEA IVN stack along with the CAN receive and transmit function mapped. Now the system can receive all the configured messages and update data variables updated with the signal values. Callbacks were triggered on timeouts for any of these messages and suitable actions taken.
Electric Tractor Cluster - Architecture
The cluster had to support Unified Diagnostics services as well, for which the RAPIDSEA UDS server stack was utilized. All the necessary callbacks were implemented to achieve the complete diagnostics functionality including various services such as ECU Reset, Routine Control, Read DTC/Clear DTC, Read Data by ID, Write Data by ID etc. The diagnostic trouble code information and data values were backed up in NVM(EEPROM) so that it was retained across power cycles.
On top of these standard features, the tractor instrument cluster functionality was implemented. Extensive filtering was done for RPM and speedometers. Implemented as stepper motor driven gauges, zero-point detection (ZPD) algorithm was developed leveraging the underlying hardware functionality provided by RL78. On boot-up, the ZPD was run before prove-out to move the needles to zero position if not already present. Then the needle position was managed with a PID (Proportional-Integral-Derivative) controller with the Kp, Ki and Kd components fine-tuned to match the response as desired by the customer.
Apart of the cluster features, general firmware considerations like watchdog timer were added so that the cluster can always recover from unexpected software failures. The entire design was optimized for power so that it consumes sub-microwatts once it entered in to the deep-sleep state. The bootup cycle was also sped up so that the prove-out starts immediately on ignition on. EEPROM writes were optimized by preventing unnecessary writes and implementing wear levelling for ODO meter values thereby prolonging the EEPROM life.
Once the target hardware was available, the firmware was ported on to it. Finally, firmware update over CAN was implemented over UDS so that the cluster firmware can be updated at service centers when needed. Our ready-to-use CAN bootloader solution was utilized to achieve the same. The entire code was reviewed using static code analyzer and all MISRA-C violations addressed and fixed.
Our QA team validated the entire functionality with our automated testing framework - TestBot and reports submitted. Detailed power and performance profiling was done and handed over to the customer along with all the necessary documentation. Our team was present at the customer site during the last few weeks and ensured that the electric tractor instrument cluster functionality is met and start of production (SoP) done.
Embien once again proved to be a trusted partner for automotive product developments by supporting the electric tractor instrument cluster development with the following benefits.
Our ownership and flawless delivery on committed time of the tractor instrument cluster was well appreciated by the customer opening opportunities for other product developments. Even the end-customer was satisfied with the performance and quality of the cluster (especially on the response of stepper motor-based gauges) and moved our customers design to the first supplier status. Our turnkey product engineering team proved their mettle and added one more feature in our cap of successful projects. Do contact us to work together with our awesome team for your next product development!