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JColvin

Change USB JTAG clock speed

Question

A customer on our website asked the following question:

Hi,
We bought some Digilent USB JTAG cables as the website http://store.digilentinc.com/jtag-usb-cable/ and connect to our FPGA which inlcues a ARC5 CPU. We typed the command line "mdb -hard -digilent -off=check_dcache_lock_bug -nogoifmain -prop=dig_speed=100000 -connect_only" and hope the JTAG TCK is around 100KHz, but to measure the TCK by scope, the clock is always 700KHz, not 100KHz. Our goal is to adjust the TCK to 5MHz or 10MHz, could you please teach us to do the right setting?

The response is below.

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Hello,

If I'm reading your question correctly, it sounds like you are using the Synopsis metaware to change the JTAG clock speed, so you would likely need to contact Synopsis for the correct command to set the clock speed. However, I will ask some of applications engineers to see if they are aware of a way to change the JTAG clock speed.

Thanks,
JColvin

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hello,

I confirmed this with our expert of the jtag-usb. Unfortunately the clock speed is set and can not be changed.

thank you,

Jon

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Hi Jon,
Thanks for the quick answer, I'm Paddy who raised the hand of this question, I have two questions.
1. Does it limit by jtag-usb cable? Why the jtag-usb cable has this limitation?
2. Does Digilent provide jtag-usb cable which can adjust the jtag_tck by user?

Paddy

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Hello Paddy,

The jtag usb uses bit banging because of this there is no way to adjust the clock. We do have the  jtag HS1 , jtag HS2 and jtag HS3 that have the ability to change the jtag_tck.  You would need to contact Synopsis for the correct command to set the clock speed. Another route would be to make your own API using adept sdk that would allow you to set the clock speed for either of the jtag HS1 , jtag HS2 or jtag HS3.

thank you,

Jon 

Edited by jpeyron

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Hi Jon,
Synopsys has provied the command for me, -prop=dig_speed=10000000, it means the jtag_tck will run at 10MHz. Can I use the command to change jtag_tck frequency by jtag HS2/HS3 cable without to make my own Adept SDK? I only have H/W resource so to make the API may take many time.

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Hi paddy,

Yes, if Synopsys has a command to change the jtag_tck then this will be able to change the HS2 or HS3 cables and you should not need to make you own api through Adept SDK.

thank you,

Jon

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Hi Jon,
I got a JTAG-HS2 cable and it can connect to the ARC HS CPU successfully but ARC5, does the JTAG-HS2 cable supports ARC5 CPU? ARC5 is a old CPU and I can connect it by JTAG-USB cable.

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Hi Paddy,

I believe the support is actually in reverse, the ARC CPU's support certain JTAG cables. So if the ARC5 CPU does not recognize the JTAG HS2, you would need to contact Synopsis to see what could be done to add support for it.

Thanks,
JColvin

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