Ask Robb235 to attempt to start his car and take a log

Oct 13, 2025 by wbrum.org 142 views

Introduction

In this article, we will delve into a potential issue that can cause a no-start condition in a vehicle's engine. The problem arises from the operator precedence in a specific line of code, which can lead to an ambiguous condition. We will explore the bug, its reproduction steps, and the expected behavior. Additionally, we will examine the code snippet responsible for the issue and provide a solution.

Describe the Bug

The bug in question is related to the triggerSyncGapRatio, which is an incredibly out-of-range value that appears in the logs preceding the no-start conditions. This issue is not only frustrating but also poses a significant problem for vehicle owners who rely on their cars for daily use.

Hardware

The hardware involved in this issue includes:

Board: uaefi
Engine info: 5vz-fe 36-2 trigger wheel

To Reproduce

To reproduce the behavior, follow these steps:

Ask Robb235 to attempt to start his car and take a log: The first step is to ask the user to attempt to start their car and take a log of the process.
No-start condition persists: The no-start condition persists, and the engine does not start. This is a crucial step in reproducing the issue.
Look at the logs, notice massive trigger latest ratio being logged: After the no-start condition, look at the logs and notice the massive trigger latest ratio being logged. This is a key indicator of the issue.
Engine doesn't start: The engine does not start, and this is the expected behavior.
Flip to opposite phase, engine starts, but has two long teeth in the trigger log: If you flip to the opposite phase, the engine starts, but it has two long teeth in the trigger log. This is an indication of the wrong edge.

Expected Behavior

The expected behavior is that the engine starts without showing two long teeth, indicating the wrong edge. This is the desired outcome, and any deviation from this behavior is a cause for concern.

Screenshots

The following screenshots provide visual evidence of the issue:

Potential Bug

The potential bug is located in the following code snippet:

https://github.com/rusefi/rusefi/blob/master/firmware/controllers/trigger/trigger_decoder.cpp#L458C27-L458C32

The issue arises from the operator precedence in the following line of code:

if (triggerShape.isSynchronizationNeeded) {
    triggerSyncGapRatio = (float)toothDurations[0] / toothDurations[1];

The problem is that the typcast takes higher precedence over the / operator, leading to an ambiguous condition. This can cause the triggerSyncGapRatio to be calculated incorrectly, resulting in the no-start condition.

Solution

To solve this issue, we need to modify the code to ensure that the / operator takes precedence over the typcast. We can do this by using parentheses to group the expression:

if (triggerShape.isSynchronizationNeeded) {
    triggerSyncGapRatio = (float)(toothDurations[0] / toothDurations[1]);

By adding the parentheses, we ensure that the / operator is evaluated first, and the typcast is applied to the result. This should resolve the issue and prevent the no-start condition.

Conclusion

Introduction

In our previous article, we explored the potential issue of operator precedence causing a no-start condition in a vehicle's engine. We delved into the bug, its reproduction steps, and the expected behavior. We also examined the code snippet responsible for the issue and provided a solution. In this article, we will answer some frequently asked questions related to this issue.

Q: What is the root cause of the no-start condition?

A: The root cause of the no-start condition is the ambiguous condition caused by the operator precedence in the code snippet. Specifically, the typcast takes higher precedence over the / operator, leading to an incorrect calculation of the triggerSyncGapRatio.

Q: How can I reproduce the issue?

A: To reproduce the issue, follow these steps:

Ask Robb235 to attempt to start his car and take a log.
The no-start condition persists, and the engine does not start.
Look at the logs, notice the massive trigger latest ratio being logged.
The engine does not start.
Flip to the opposite phase, engine starts, but has two long teeth in the trigger log.

Q: What is the expected behavior?

A: The expected behavior is that the engine starts without showing two long teeth, indicating the wrong edge.

Q: How can I fix the issue?

A: To fix the issue, modify the code to ensure that the / operator takes precedence over the typcast. You can do this by using parentheses to group the expression:

if (triggerShape.isSynchronizationNeeded) {
    triggerSyncGapRatio = (float)(toothDurations[0] / toothDurations[1]);

Q: What are the consequences of not fixing the issue?

A: If the issue is not fixed, it can lead to a no-start condition, which can be frustrating and inconvenient for vehicle owners. Additionally, it can also cause damage to the engine and other components.

Q: Can this issue occur in other situations?

A: Yes, this issue can occur in other situations where the operator precedence is not correctly handled. It is essential to be aware of this potential issue and take steps to prevent it.

Q: How can I prevent this issue in the future?

A: To prevent this issue in the future, follow these best practices:

Be aware of the operator precedence in your code.
Use parentheses to group expressions correctly.
Test your code thoroughly to ensure that it works as expected.

Conclusion

In conclusion, the potential operator precedence causing no-start issue is a complex problem that requires careful analysis and debugging. By understanding the bug, its reproduction steps, and the expected behavior, we can identify the root cause of the issue. By following the solution and best practices outlined in this article, we can prevent this issue and ensure that our code works correctly.