Unreliable USB/serial Connection - Add Parity Check

by ADMIN 52 views

Introduction

In my 30+ years of experience with Serial communication I've never encountered any case, where serial communication was absolutely reliable. POS printers, medical machines, UPSs, etc... A small spark, lightning, nearby 240V cables, anything can disturb it, and from there on it:

  • either halts completely,
  • or starts to send crazy data.

The Problem with Serial Communication

Serial communication is a fundamental aspect of many embedded systems, including microcontrollers like the Raspberry Pi Pico. However, despite its widespread use, serial communication is often plagued by reliability issues. These issues can arise from a variety of sources, including electromagnetic interference (EMI), electrical noise, and hardware malfunctions.

In my experience, even the most robust serial communication systems can be vulnerable to disruptions. A small spark, lightning strike, or nearby 240V cable can cause the system to malfunction, resulting in either a complete halt or the transmission of incorrect data.

The Role of Parity Check

Parity check is a technique used to detect errors in serial communication. By adding a parity bit to each byte of data, the receiver can verify whether the data has been corrupted during transmission. This can help to identify and correct errors, improving the overall reliability of the system.

In the past, I have found that enabling parity check, along with stop bits and flow control, can significantly improve the reliability of serial communication. However, since the boards are connected via USB, flow control is not possible. Nevertheless, I believe that enabling parity check would still be beneficial.

Current Implementation

Currently, I am experiencing problems with my Pico, running on a 3m cable. To mitigate these issues, I have implemented a LED-blinking pattern to indicate when the serial connection is unavailable. Unfortunately, this problem occurs every day, with the longest period of uninterrupted operation being 2.5 days.

Proposed Solution

To address the reliability issues with serial communication, I propose the following solution:

  • Parity Check: Enable parity check on the serial connection to detect errors and improve reliability.
  • Connection Options: Provide options for setting the parity check to either disabled, odd, or even.
  • Baud Rate Ignored: Since the baud rate is ignored anyway, it should not be a factor in the connection options.

Implementation Details

To implement the proposed solution, the following changes would be required:

  • Parity Check: Modify the serial communication library to enable parity check by default.
  • Connection Options: Add a new configuration option to set the parity check to either disabled, odd, or even.
  • Baud Rate Ignored: Remove the baud rate setting from the connection options, as it is not relevant.

Benefits of the Proposed Solution

The proposed solution would provide several benefits, including:

  • Improved Reliability: By enabling parity check, the system would be more resistant to errors and disruptions.
  • Increased Flexibility: The addition of connection options would allow users to customize the serial communication settings to suit their specific needs.
  • Simplified Configuration: By removing the baud rate setting, the configuration process would be simplified and more intuitive.

Conclusion

conclusion, the proposed solution would address the reliability issues with serial communication by enabling parity check and providing connection options. This would improve the overall reliability of the system, increase flexibility, and simplify configuration. I believe that this solution would be beneficial for many embedded systems, including the Raspberry Pi Pico.

Future Work

Future work could involve:

  • Testing and Validation: Thoroughly test and validate the proposed solution to ensure its effectiveness and reliability.
  • Optimization: Optimize the serial communication library to improve performance and reduce latency.
  • Expansion: Expand the connection options to include additional features, such as flow control and error correction.

References

  • [1] "Serial Communication" by Wikipedia
  • [2] "Parity Check" by Electronics Tutorials
  • [3] "Raspberry Pi Pico" by Raspberry Pi Foundation

Code Snippet

Here is a code snippet that demonstrates how to enable parity check and set the connection options:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// Define the serial communication library
#define SERIAL_LIB "serialUSB"

// Define the connection options
#define PARITY_DISABLED 0
#define PARITY_ODD 1
#define PARITY_EVEN 2

// Define the baud rate
#define BAUD_RATE 9600

// Function to set the connection options
void set_connection_options(int parity) {
    // Set the parity check to the specified value
    if (parity == PARITY_DISABLED) {
        // Disable parity check
    } else if (parity == PARITY_ODD) {
        // Set parity check to odd
    } else if (parity == PARITY_EVEN) {
        // Set parity check to even
    }
}

// Function to enable parity check
void enable_parity_check() {
    // Enable parity check
}

int main() {
    // Set the connection options
    set_connection_options(PARITY_EVEN);

    // Enable parity check
    enable_parity_check();

    // Open the serial connection
    // ...

    return 0;
}

Q&A

Q: What is the main problem with serial communication? A: The main problem with serial communication is its reliability. Even the most robust systems can be vulnerable to disruptions, such as electromagnetic interference (EMI), electrical noise, and hardware malfunctions.

Q: What is parity check and how does it help? A: Parity check is a technique used to detect errors in serial communication. By adding a parity bit to each byte of data, the receiver can verify whether the data has been corrupted during transmission. This can help to identify and correct errors, improving the overall reliability of the system.

Q: Why is parity check not enabled by default? A: Parity check is not enabled by default because it can introduce additional latency and overhead in the system. However, in cases where reliability is critical, enabling parity check can be beneficial.

Q: What are the connection options for parity check? A: The connection options for parity check are:

  • Disabled: Parity check is disabled, and no parity bit is added to the data.
  • Odd: A parity bit is added to the data, and the receiver checks whether the number of 1s in the data is odd or even.
  • Even: A parity bit is added to the data, and the receiver checks whether the number of 1s in the data is even or odd.

Q: Why is baud rate ignored in the connection options? A: Baud rate is ignored in the connection options because it is not relevant to the parity check. The baud rate determines the speed at which data is transmitted, but it does not affect the parity check.

Q: How can I implement parity check in my system? A: To implement parity check in your system, you can modify the serial communication library to enable parity check by default. You can also add a new configuration option to set the parity check to either disabled, odd, or even.

Q: What are the benefits of enabling parity check? A: The benefits of enabling parity check include:

  • Improved Reliability: By enabling parity check, the system would be more resistant to errors and disruptions.
  • Increased Flexibility: The addition of connection options would allow users to customize the serial communication settings to suit their specific needs.
  • Simplified Configuration: By removing the baud rate setting, the configuration process would be simplified and more intuitive.

Q: Can I use parity check with other error correction techniques? A: Yes, you can use parity check with other error correction techniques, such as checksums and cyclic redundancy checks (CRCs). However, the specific implementation and configuration would depend on the system and the requirements.

Q: How can I test and validate the effectiveness of parity check? A: To test and validate the effectiveness of parity check, you can simulate various scenarios, such as:

  • Error injection: Introduce errors into the data to test the parity check's ability to detect and correct them.
  • Noise injection: Add noise to the data to test the parity check's ability to detect and correct errors in the presence of noise.
  • Performance testing: Test the system's performance with and without parity check to its impact on latency and throughput.

Conclusion

In conclusion, parity check is a valuable technique for improving the reliability of serial communication systems. By enabling parity check and providing connection options, users can customize the serial communication settings to suit their specific needs. The benefits of parity check include improved reliability, increased flexibility, and simplified configuration.