Decodes USB wireshark data into JTAG command layer (and higher)
Use wireshark to export parsed FTDI frames from a USB capture to JSON
(File -> Export Packet Dissections -> As JSON ...). usb_jtag_decoder.py
takes input as --json_pcap <input file>. usb_jtag_decoder.py can generate
the following output:
- Output decoded FTDI commands to JSON with
--ftdi_commands <output JSON> - Print the state of the JTAG simulation with the following flags:
--print_transitions- Print JTAG transitions, except for DRSHIFT and IRSHIFT.--print_dr_shift-- Print JTAG DRSHIFT transitions if--print_transitionsis supplied.--print_ir_shift-- Print JTAG IRSHIFT transitions if--print_transitionsis supplied.
This decoder assumes FTDI chip has the JTAG interface on interface A, with pin 0 as TCK, pin 1 as TDI, pin 2 as TDO, and pin 3 as TMS.
Simply converting JTAG signals into JTAG state transitions is not immediately
useful on its own. However to decode any further requires a particular JTAG
chain to be modelled. This repository provides a simple model of the Zynq
UltraScale+ MPSoC JTAG chain. This model can by invoking
usb_jtag_zynq_mpsoc_decoder.py. The --json_pcap argument is the same as
before. The output of the decoder is sent to the file specified by
--openocd_script. This output is an approximation of an OpenOCD script
issuing commands to the target.
Recent versions of Wireshark (3.2.1+) can directly capture from USB if enabled. See https://wiki.wireshark.org/CaptureSetup/USB
Wireshark needs to know which USB bus the JTAG programmer is connected too.
lsusb can be used to both reports device names and their attached bus.
USB Pcap (https://desowin.org/usbpcap/) can be used to generate Wireshark pcanp files. Simply install and run USBPcapCMD and follow the prompts. Select the USB device that represents the FTDI programmer. After the capture is complete, use a recent version of Wireshark (3.2.1+) to open the file and output the decoded frames per the earlier instructions.