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RE: Unable to download codes with GDB
by firefalcon on May 17, 2011
firefalcon
Posts: 99
Joined: Jan 10, 2011
Last seen: Mar 26, 2024
Im using xilinx spartan 3e starter kit with a real JTAG cable (DLC9G), so I uncommented `define GENERIC_TAP in minsoc_defines.v. as it is said in FAQS.

what can be the mistake?

Thanks in anticipate.


The built-in DLC9 is not a real JTAG cable. You need to have GENERIC_TAP commented and uncomment FPGA_TAP and XILINX_FPGA.
RE: Unable to download codes with GDB
by franib on May 17, 2011
franib
Posts: 5
Joined: Aug 21, 2010
Last seen: May 25, 2011
Thanks firefalcon.

The cable I have is not the DCL9, mine is DCL9G what is from computer usb to a blackbox and from blackbox JTAG (tdi,tdo,tck,etc.)to FPGA board.

Then I uncomment define GENERIC_JTAG and define XILINX_FPGA, comment define FPGA_TAP.

is it right?
RE: Unable to download codes with GDB
by nyawn on May 18, 2011
nyawn
Posts: 173
Joined: Dec 19, 2008
Last seen: May 31, 2023
Thanks firefalcon.

The cable I have is not the DCL9, mine is DCL9G what is from computer usb to a blackbox and from blackbox JTAG (tdi,tdo,tck,etc.)to FPGA board.

Then I uncomment define GENERIC_JTAG and define XILINX_FPGA, comment define FPGA_TAP.

is it right?


If you were using a stand-alone JTAG cable (DLC9 or any other), and attaching it to a JTAG port you created using the GPIO pins of the FPGA, then using GENERIC_JTAG would be correct.

However, based on the JTAG chain enumeration output by adv_jtag_bridge, that's not what you're doing. Your JTAG chain has 3 Xilinx devices on it including your FPGA, meaning that you are attaching your JTAG cable to the dedicated JTAG port of the FPGA, the same port you use to download the bitstream to the FPGA. In this case, you need to use FPGA_TAP and XLINIX_FPGA.

If you want to know more about why, I suggest you read the top-level documentation for the adv. debug system, it gives an overview of the various TAP modules and when they're used.

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