Understanding USBlyzer Interface
Before diving into logs, it's crucial to familiarize yourself with the USBlyzer interface. USBlyzer is a powerful USB protocol analysis tool that provides detailed information about USB traffic. Once logs are captured, they'll display events, request details, and statuses crucial for troubleshooting.
Identifying the Problematic Endpoint
- Device Descriptor: Review the device descriptors to ensure that they are properly configured and support the endpoints you need. An error in descriptor settings often leads to connectivity issues.
- Endpoint Errors: Analyze the endpoint involved in the error. USBlyzer logs will indicate if there are timeouts or stalls, which might reveal communication errors on specific endpoints.
- Log Filters: Use USBlyzer’s filtering options to narrow down logs to specific devices or types of transfers. This helps in isolating the faulty communications between host and device.
Analyzing Control Transfer Issues
- Setup Packets: Evaluate setup packets, especially for standard requests. Any deviation or malformed setup packet might indicate a firmware-level issue.
bmRequestType: 0x80
bRequest: 0x06
wValue: 0x0100
Verify if the request and the response correspond correctly. Issues here can stem from incorrect device behavior at the firmware level.
- Stall and NAK Responses: Look for repeated STALL or NAK responses, as they indicate the device isn’t processing control transfer requests properly.
Evaluating Data Transfer Errors
- Bulk Transfers: During bulk data errors, you should review the sequence of packets to identify missing or out-of-order transmissions.
IN: Data: 0xFA, 0xCE, 0xBE, 0xAD
OUT: Data: 0xDE, 0xAD, 0xC0, 0xDE
STATUS: 0x00
Check the completion status code for errors and verify if the length of data matches what was expected.
- Isochronous Transfers: These are particularly prone to timing issues. Look for the periodicity of packet delivery and whether the logs show any data underflows which may point towards a firmware buffer mismanagement.
Debugging Interrupt Transfers
Polling Intervals: Verify if the interrupt endpoint's polling interval aligns with the device's capability. Mismatched expectations can cause failures and are logged as errors.
Unexpected Data: Confirm that the interrupt data returned matches expected forms. Unintended data might suggest issues in data interpretation at the firmware level.
Interpreting Error Codes and Status
- Common Error Codes: Familiarize yourself with common completion codes:
- 0x00: Successful completion.
- 0x01: Stall detected.
- 0x02-0x05: Various communication errors which indicate issues with data reception or device availability.
Analyze these against the specification to determine firmware-level adjustments that may be required.
Analyzing Timings and Delays
Log Timestamps: Compare timestamps for sent requests and received responses. Large variances suggest latency issues which may stem from inefficient firmware processing or resource constraints.
Transaction Time: Ensure that the transaction windows align with expected USB timing parameters defined in specifications, adjusting firmware timing as needed.
Using USBlyzer's Scripting Interface
USBlyzer provides a scripting API, which can be used to automate the troubleshooting process or to log specific conditions that are otherwise difficult to replicate or pinpoint.
# Example script to capture specific transmissions
create_filter = {
"device_id": "your_device_id_here",
"transfer_type": "Control",
}
usblyzer.capture(**create_filter)
By using these filtering and scripting capabilities, a firmware developer can deepen insights into problematic transmissions. As always, armed with detailed log analysis, any corrective actions should align with maintaining compliance with USB standards while optimizing the specific behavior of firmware communications.