Real-time control software design the first week of work-automotive ABS software system case study

Case analysis of automotive ABS software system

ABS through the control action on the wheel brake sub-pump brake line pressure, so that the car in the emergency braking wheel will not hold, so that the car in emergency braking can still maintain a good direction stability.

ABS system is generally installed on the basis of general braking system wheel speed sensor, electronic control unit, brake pressure regulator. When braking, through the analysis of the sensor speed wheel speed data to determine whether the wheel is in the hold-slip state, and accordingly control the brake pressure regulator for high-frequency pressurization, pressure, decompression, to prevent the wheel to hold dead.

Q1. What are the strong real-time functional requirements of this system? Which real-time events need to be responded to in real time, and the magnitude of the allowed real-time delay is estimated.

A1. Strong real-time requirements: Read the sensor data and analyze and control the brake pressure regulator.

Estimated delay order of magnitude: for 60/3.6km/h speed brake simulation slip rate change curve, according to 6s-14s curve fluctuation, estimated allowable delay order of magnitude 0.1s

Q2. If you are a software designer, to implement these real-time functions, design several real-time tasks?

A2. Task one: Get sensor data

Task two: Analysis and calculation, to determine the braking situation

Task Three: Send instructions to the brake pressure regulator

Q3. What are the time-triggered or event-triggered tasks, and if it is time-triggered, what is the period?

A3. Task one gets the sensor data for the time trigger, the period is lower than the allowable delay time, estimated to be 50ms

Task two analysis is calculated as a time trigger, and the period is estimated to be half of the sensor cycle, 25ms

Task three send command for TIME trigger, continuously to the brake regulator to send instructions for control, the period is less than two cycles of the task, estimated to be 25ms

Q4. Are these real-time tasks independent of each other or are there certain dependencies? Analyze this dependency.

A4. There is a dependency relationship. The sensor data is required for calculation, and the sensor data needs to be processed in time after it is in place. Send instructions in a timely manner when the results are analyzed.

Q5. Are there any shared hardware resources that need to be used between these real-time tasks? Lists this dependency.

A5. All need to occupy CPU, memory, and possibly a communication bus.

Real-time control software design the first week of work-automotive ABS software system case study