KC705 JTAG chain and FMC HPC connector

[geerard]

When I connect a 3rd party board (TI ADC12D1600RFRB) to the FMC HPC connector, I loose connection with the JTAG chain and I am unable to program the FPGA. According to me, it is the JTAG bypass switch which is opened by HPC pin H2, which is connected to ground on the daughter board. The JTAG pins on the HPC connector (D29-D31) of the daughter board are not connected, neither bypassed.

Is there a way to bypass this JTAG switch (U76) manually on the KC705?

[tud_hartmann · Accepted solution]

@geerard

Hi,

dirty hack is to short pins 1 and 2 of the U76.

Best Regards,

Stephan

[geerard]

In the mean time, I've also found a topic on the TI E2E forum describing this issue on a similar board, confirming your proposal.

https://e2e.ti.com/support/data_converters/high_speed_data_converters/f/68/p/394209/1393474

[gnarahar]

@geerard Or one way would be to pull R9.1 pin to Ground. Whichever works for you. 

Btw is U76 broken on your KC705?

Is it still under warranty? If not, then the above suggested methods would be the only hack which you would need to revert back when you remove the FMC daughter card. 

[geerard]

@gnarahar,

The U76 is not broken, and pulling R9.1 pin to ground would permanently open the JTAG chain, regardless of whether or not an FMC board is connected. This is thus not an option. Shorting this R9 is also not an option, since the pin on the ADC board is direcly connected to the ground plane, which would create very large currents.

[gnarahar]

@geerard My bad. I missed the point in your original post about JTAG pins on the FMC daughter card not being connected. 

Yeah, R9.1 doesn't help. Shorting Pins 1 & 2 of U76 is the only way to go. 

[umamahe]

As it mentioned in previous post TDI and TDO short is one option.

Before that please check the JTAG chain connections carefully. Especially TDO-TDI-TDO-TDI loop,  There could be some extra loops for JTAG connections. Also make sure TCK and TMS connected to all devices including third party device.

Is third party device is as per JTAG IEE1149.1 standard? 

[naarayananrao]

Hello Giri

How do you short it? Do you have any jumpers in the board? Or is there any other way?

[geerard]

This is an error on the daughterboard and could not be foreseen by Xilinx. Therefore, no jumpers were included on the KC705 and manual soldering is required.

[naarayananrao]

Thank you very much. I guess shorting both U76 and U77 will be required as I will be using both HPC and LPC connectors.

[geerard]

Keep in mind that these shorts are only needed if the daughterboard does not have the JTAG pins linked through, which was the case with the board I was using. If you take a daughterboard that is VITA 57.1 compliant or where the JTAG pins (TDI and TDO) are connected, this manual patch would not be needed. Furthermore, I believe the daughterboard I was using was incompatible with the LPC connector, if I'm correct.

[naarayananrao]

Hello @geerard 

I am using a KC705 board and the FMC Connector cables I am using are VITA 57.1 compliant too. But I loose the JTAG programmability when I connect the cables. I am also clueless which pins in the Switch to short. I has two one one side and 3 pins to the other as given below. My guess I am supposed to the two on the right side to close the switch as marked yellow in the picture. Am I right? 

Also it says so in the KC705 documentation.

[naarayananrao]

Sorry my bad. I got to know to which of the pins to short.

[markg@prosensing.com]

@naarayananrao 

To regain JTAG operation, you can modify the FMC daughter board instead of modifying the KC705.

For example, if you are using the XM105 daughter board, you can short two pins on the XM105 as described in the following AR.

https://www.xilinx.com/support/answers/52888.html

[naarayananrao]

Thank you professor.

I am looking into using alternative methods for programming the FPGA using Linear or Quad SPI flash as currently I don't have an access to a solder.