Set maximum captured packet size to 1027 #56
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GitHub switched off git protocol on March 15, 2022.
Add new prebuilt ov3.fwpkg generated with Xilinx ISE 14.7. Gateware make test target is no longer working at least since commit e6f25c4 ("Initial update to current migen") where Migen was updated to version no longer containing old simulator. Icarus, needed by ov3 gateware tests was removed in Migen commit f1dc008d324d ("Simulator will be rewritten"). Unfortunately, my very limited FHDL knowledge is not enough to fix the tests.
Do not immediately proceed to writing header when packet larger than MAX_PACKET_SIZE is captured on the bus. Keep counting packet length so the value can be reported to the host. When Truncated flag is set the size reported in header is untruncated packet size and only MAX_PACKET_SIZE bytes are included. In order to not increase header size, and thus limit the maximum capture throughput, the MAX_PACKET_SIZE value must match between gateware and host. Because change modifies gateware to host software protocol and hence is backwards incompatible. I believe the gateware should be considered integral part of software package and therefore I do not consider this protocol incompatibility to be a problem, especially that the gateware is only loaded to volatile memory. Reporting actual length as seen on the bus allows USBInterpreter to display for example "Truncated 2 bytes" instead of "Unexpected ERR CRC". Similarly, when exporting to pcap format, Wireshark can display "[Packet size limited during capture]" instead of reporting CRC errors.
USB 2.0 maximum possible packet size is 1027. The packet is 1027 bytes when wMaxPacketSize is 1024 (interrupt or isochronous high-speed) and 1024 bytes are transferred in single transaction (1 byte PID + 1024 bytes data + 2 bytes CRC).
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This looks good to me, thank you! Loss of the ability to test is unfortunate but I realize it would take significant effort to bring it back. FYI - https://github.com/OpenVizslaTNG/ov_ftdi is now used for development. The same change should apply there. |
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Opened OpenVizslaTNG#14 |
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Report untruncated packet size to host
Do not immediately proceed to writing header when packet larger than MAX_PACKET_SIZE is captured on the bus. Keep counting packet length so the value can be reported to the host.
When Truncated flag is set the size reported in header is untruncated packet size and only MAX_PACKET_SIZE bytes are included. In order to not increase header size, and thus limit the maximum capture throughput, the MAX_PACKET_SIZE value must match between gateware and host.
Because change modifies gateware to host software protocol and hence is backwards incompatible. I believe the gateware should be considered integral part of software package and therefore I do not consider this protocol incompatibility to be a problem, especially that the gateware is only loaded to volatile memory.
Reporting actual length as seen on the bus allows USBInterpreter to display for example "Truncated 2 bytes" instead of "Unexpected ERR CRC". Similarly, when exporting to pcap format, Wireshark can display "[Packet size limited during capture]" instead of reporting CRC errors.
USB 2.0 maximum possible packet size is 1027. The packet is 1027 bytes when wMaxPacketSize is 1024 (interrupt or isochronous high-speed) and 1024 bytes are transferred in single transaction (1 byte PID + 1024 bytes data + 2 bytes CRC).
Fixes: #29