Most devices of the current Freescale PowerPC series support the data trace method of Nexus Class 3. In this case, the developer configures one or two monitoring windows with a maximum total size of 512 kByte in the ECU RAM. Any changes within these monitoring windows are transmitted to the POD via Nexus Class 3 without any additional CPU load. Transmission rates for raw data of up to 100 MByte/s are possible over the High Speed Serial Link cable. The advantage of this concept is that the base module for measurement data always contains a consistent mirrored RAM of the ECU’s RAM. An ECU software trigger interrupts the data flow within the measurement data base module, where new changes are saved in a First In, First Out (FIFO) buffer in RAM. The measurement is initiated by one of up to 256 different software triggers, and the contents of the mirrored RAM are “frozen”. Based on the measurement configuration, the signals are read out from the mirrored RAM in the base module for measurement data and are sent to the measurement and calibration tool over XCP on Ethernet (Figure 2).
Figure 2: Data flow concept of measurement signals by the data trace concept and Nexus Class 3 interface
Advantages of the Nexus Class 3 solution:
• The maximum measurement data rate of 30 Mbyte/s is a factor of 30 times larger than with Nexus Class 2+ and 600 times larger than with XCP on CAN.
• The CPU is typically not loaded by the measurement.
All PWM drive signals can be measured at the 100 kHz sampling rate without any problems.
The disadvantage of this solution lies in the fact that significant effort is involved in connecting the POD with its 25 pins to the microcontroller, and it must process a very large raw data stream of 100 Mbyte/s.
Data trace concept for next generation microcontrollers
The main disadvantage of the Nexus Class 3 solution will be eliminated in next generation microcontrollers, because the pin count has been reduced from 25 to 5. However, the measurement data rate and sampling rate will remain at the same unchanged high level. This data trace solution will also be supported by future processors from the Infineon and Freescale companies. The raw data stream von 100 Mbyte/s must still be processed.