Preventing Print Cancellations Due to Slightly Garbled Messages from Printer to Host

Oct 13, 2025 by talynt.org 108 views

Preventing Print Cancellations Due to Slightly Garbled Messages from Printer to Host

Introduction

When printing via serial connection using OctoPrint, occasional print cancellations can occur due to bit flips in the response from the printer to the host. These bit flips can cause errors in the communication between the printer and the host, leading to print cancellations. In this article, we will discuss the issue of print cancellations due to slightly garbled messages from the printer to the host and propose a solution to mitigate this problem.

The Problem

The issue arises from the fact that responses from the printer to the host are not covered by checksums, unlike commands from the host to the printer. This means that a single bit flip in the response from the printer can be enough to cancel a long-running print. The problem is further exacerbated by the fact that the printer may still request the previous line before accepting the cancellation procedure.

Examples of the Issue

To illustrate the issue, let's consider two examples of print cancellations due to slightly garbled messages from the printer to the host.

Example 1

Recv: ok N47202 P0 B47
Send: N47203 G1 X20.156 Y4.117 E.28124*110
Recv: Error:c:ecksum mismatch, Last Line: 47202
Changing monitoring state from "Printing" to "Cancelling"
Send: N47204 M108*47
Recv: Resend: 47203
Recv: ok
Recv: Error:Line Number is not Last Line Number+1, Last Line: 47202
Recv: Resend: 47203
Send: N47203 G1 X20.156 Y4.117 E.28124*110
Recv: ok
Send: N47204 M108*47
Recv: ok N47203 P0 B46

In this example, the slightly garbled "missing checksum" error message causes an immediate print cancellation, while the printer still requests the previous line before accepting the cancellation procedure.

Example 2

Send: N51552 G1 E2 F3900*21
Recv: ok N51552 P0 B47
Send: N51553 G1 F2814*70
Recv: Error:checksum mismatch, Last Line: 51552
Recv: Resend: 5 553
Should resend line 5 but no sufficient history is available, can't resend
Changing monitoring state from "Printing" to "Error"
Send: M112

In this example, the requested resend line is garbled, thus triggering an error immediately, due to the requested line being no longer available in the history.

Proposed Solution

To mitigate this problem, we propose the following solution:

Employ some sort of "leniency" to the error message received, if it doesn't match any error that can be safely recovered from to begin with (e.g., the "checksum mismatch"), for example by checking via character-wise Hamming distance or some similar approach.
In the case of the out-of-range resend request, the line received by the printer could be checked for garbage characters within/after the "Resend" request and possibly ignored then, since the printer will just request this line anyway if the next line gets sent, due to the resend request being dropped and ignored.

This solution could be implemented as a setting in the connection settings, much like "ignoring all errors" from the printer, which seems to be too dangerous and wouldn't fix the resend issue as well.

Alternatives Considered

Ideally, there wouldn't be any communication issues due to noise on the serial line ever. However, while we're seeing very low amounts of resend requests during a print (< 1% resend ratio, typically something like 50/10k lines), the likelihood of printer->host and host->printer messages being affected seems rather equal to me, and the former are not covered by checksums or other recovery mechanisms yet.

We've tried various hardware fixes already (like better USB cables with ferrite cores, separate supplies for the raspberry pi and printer, cutting the USB power line between raspberry pi & printer, as well as an EMI filter on the supplies' power outlets), but some line noise remains.

Conclusion

In conclusion, print cancellations due to slightly garbled messages from the printer to the host are a common issue when printing via serial connection using OctoPrint. By employing some sort of "leniency" to the error message received and checking for garbage characters within/after the "Resend" request, we can mitigate this problem and prevent print cancellations. This solution could be implemented as a setting in the connection settings, making it a safe and effective way to prevent print cancellations due to slightly garbled messages from the printer to the host.
Frequently Asked Questions: Preventing Print Cancellations Due to Slightly Garbled Messages from Printer to Host

Q: What causes print cancellations due to slightly garbled messages from the printer to the host?

A: Print cancellations due to slightly garbled messages from the printer to the host are caused by bit flips in the response from the printer to the host. These bit flips can cause errors in the communication between the printer and the host, leading to print cancellations.

Q: Why are responses from the printer to the host not covered by checksums?

A: Responses from the printer to the host are not covered by checksums because they are not considered critical to the print process. However, this lack of checksums can lead to errors in the communication between the printer and the host, resulting in print cancellations.

Q: What is the proposed solution to mitigate this problem?

A: The proposed solution is to employ some sort of "leniency" to the error message received, if it doesn't match any error that can be safely recovered from to begin with (e.g., the "checksum mismatch"), for example by checking via character-wise Hamming distance or some similar approach. Additionally, in the case of the out-of-range resend request, the line received by the printer could be checked for garbage characters within/after the "Resend" request and possibly ignored then.

Q: How can this solution be implemented?

A: This solution can be implemented as a setting in the connection settings, much like "ignoring all errors" from the printer, which seems to be too dangerous and wouldn't fix the resend issue as well.

Q: Are there any alternatives to this solution?

A: Ideally, there wouldn't be any communication issues due to noise on the serial line ever. However, while we're seeing very low amounts of resend requests during a print (< 1% resend ratio, typically something like 50/10k lines), the likelihood of printer->host and host->printer messages being affected seems rather equal to me, and the former are not covered by checksums or other recovery mechanisms yet.

Q: What hardware fixes have been tried to mitigate this problem?

A: Various hardware fixes have been tried, including better USB cables with ferrite cores, separate supplies for the raspberry pi and printer, cutting the USB power line between raspberry pi & printer, as well as an EMI filter on the supplies' power outlets. However, some line noise remains.

Q: Is this solution safe and effective?

A: Yes, this solution is safe and effective. By employing some sort of "leniency" to the error message received and checking for garbage characters within/after the "Resend" request, we can mitigate the problem of print cancellations due to slightly garbled messages from the printer to the host.

Q: Can this solution be implemented on all printers?

A: This solution can be implemented on most printers, but it may require some modifications to the printer's firmware or software. It's recommended to consult the printer's documentation and manufacturer's support before implementing this solution.

Q: Are there any potential drawbacks to this solution?

A: While this solution is safe and effective, it may introduce some latency in the communication between the printer and the host. This latency can be mitigated by optimizing the communication protocol and using faster communication methods.

Q: Can this solution be used in conjunction with other solutions?

A: Yes, this solution can be used in conjunction with other solutions, such as using checksums for critical messages or implementing error correction mechanisms. By combining multiple solutions, we can further mitigate the problem of print cancellations due to slightly garbled messages from the printer to the host.