tcpdump mailing list archives
Re: Speed specific Link-Layer Header Types for USB 2.0
From: Tomasz Moń via tcpdump-workers <tcpdump-workers () lists tcpdump org>
Date: Mon, 09 May 2022 16:21:36 +0200
--- Begin Message --- From: Tomasz Moń <desowin () gmail com>
Date: Mon, 09 May 2022 16:21:36 +0200
On Mon, 2022-05-09 at 07:47 +0200, Tomasz Moń wrote:The problematic case (and the reason why full/low-speed bus is mentioned) is the LINKTYPE_USB_2_0_FULL_SPEED. It is the case when you capture at the connection between full speed hub and the host (and possibly full speed device connected to a full speed hub if there arelow speed devices connected to the full speed hub).The low speed packets (after the PRE packet) intended for low-speed device connected to full-speed hub downstream port, do appear on the link between full-speed hub and full-speed device.If there is low speed device connected to downstream hub port, then when the host wants to send packets to the low speed device, these will be sent at low speed to the hub. However, there will be PRE packet (sent at full speed) before every low speed transaction. Hopefully I have recently found full-speed only hub (thanks to Linux kernel bug report [1]), so I have all the equipment necessary to check how the OpenVizsla deals with the problematic case. [1] https://bugzilla.kernel.org/show_bug.cgi?id=213839OpenVizsla does not handle this case. While the PRE packet is correctly captured, the low-speed data is just exported by gateware as invalid packet. Similarly, the LambdaConcept USB2 sniffer does not handle this. LCSniff displays the "ERR/PRE Packet" colored in red (with no indication of the low-speed data). When OpenVizsla is configured to capture low-speed connection with the capture cable connected between host and full-speed hub, the data is just garbled. The only way to capture the low-speed data (with OpenVizsla configured to capture low-speed) is to capture it between the full-speed hub downstream port and low-speed device. I am not really surprised that both OpenVizsla and LambdaConcept USB2 sniffer fail at this problematic case. This is a corner case really, and it is not that much relevant nowadays where majority of hubs are high-speed capable. When the high-speed hub is connected to high-speed host, there is no problem with full/low speed packets as each downstream port receives data at target device speed. I am not sure if the capture problem can be solved with current OpenVizsla and LambdaConcept USB2 sniffer design. If possible, then the necessary changes would require gateware modifications.
--- End Message ---
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Current thread:
- Re: Speed specific Link-Layer Header Types for USB 2.0, (continued)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Tomasz Moń via tcpdump-workers (May 09)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Guy Harris via tcpdump-workers (May 09)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Tomasz Moń via tcpdump-workers (May 09)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Guy Harris via tcpdump-workers (May 09)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Guy Harris via tcpdump-workers (May 09)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Tomasz Moń via tcpdump-workers (May 09)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Guy Harris via tcpdump-workers (May 09)
- Re: Speed specific Link-Layer Header Types for USB 2.0 Tomasz Moń via tcpdump-workers (May 08)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Guy Harris via tcpdump-workers (May 09)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Tomasz Moń via tcpdump-workers (May 09)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Tomasz Moń via tcpdump-workers (May 09)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Guy Harris via tcpdump-workers (May 09)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Tomasz Moń via tcpdump-workers (May 09)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Guy Harris via tcpdump-workers (May 09)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Tomasz Moń via tcpdump-workers (May 09)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Tomasz Moń via tcpdump-workers (May 10)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Tomasz Moń via tcpdump-workers (Jun 13)
- Re: Speed specific Link-Layer Header Types for USB 2.0 Michael Richardson via tcpdump-workers (Jun 14)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Tomasz Moń via tcpdump-workers (Jun 19)