[SOLVED] JTAG frequency for J-Link

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  • [SOLVED] JTAG frequency for J-Link

    Hello SEGGER

    I got a question while debugging with J-link.

    I set the frequency to 100,000KHz for debugging stm32L476VET6, but the frequency value was actually set to 15,000KHz.

    Is this a frequency limit for debuggers themselves(I think GDB server's limit)? If that's right, I wonder what criteria the limit is set.

    Also, is there any way to proceed debugging with max frequency value beyond the limit?

  • Hi,
    Thank you for your inquiry and sorry for the delay in response.

    The interface speed is not limited by the J-Link GDB Server.

    The max. target interface frequencies supported by the different J-Link models can be found here:
    segger.com/products/debug-prob…nk/models/model-overview/

    Please note, that each device also has a maximum supported interface speed.
    Exceeding it is not recommended.
    You can find the values in the official product specifications of the related chip,
    or you can inquire them from the chip vendor.

    Best regards,
    Fabian
    Please read the forum rules before posting.

    Keep in mind, this is *not* a support forum.
    Our engineers will try to answer your questions between their projects if possible but this can be delayed by longer periods of time.
    Should you be entitled to support you can contact us via our support system: segger.com/ticket/
    Or you can contact us via e-mail.

  • Hi, Thank you for response.



    I debugged the JTAG frequency (specifying target interface speed) of the STm32L476VET6 MCU to 100000 kHz, but the JTAG frequency was set to 15000 kHz.

    I wonder why the JTAG frequency is automatically measured lower than the set value.

    I tested it on various MCUs and they were all fixed at 15,000khz.

    This seems to be limited because the maximum target interface speed of JLINK EDU is 15mhz, what is the difference between JLINK equipment?

  • Hi,
    I answered this question in my last post.

    Please follow the link I provided to the model overview:

    SEGGER - Fabian wrote:

    The max. target interface frequencies supported by the different J-Link models can be found here:
    segger.com/products/debug-prob…nk/models/model-overview/

    Best regards,
    Fabian
    Please read the forum rules before posting.

    Keep in mind, this is *not* a support forum.
    Our engineers will try to answer your questions between their projects if possible but this can be delayed by longer periods of time.
    Should you be entitled to support you can contact us via our support system: segger.com/ticket/
    Or you can contact us via e-mail.

  • Hello Fabian.

    Thank you for your response.

    I have a question one more thing.

    I test the stm32f103vet6 MCU with J-Link EDU.
    The J-Link EDU's target interface speed is 15MHz, and stm32f103vet6's JTAG Max speed is 10Mhz.
    But when I debugged the MCU at 15Mhz, it worked fine.

    Why is it working properly even though I debugged faster than the maximum speed?

    And if I debug faster than the original maximum speed, does something like an error message appear?

    Thank you

  • Hi,

    If the datasheet says 10 MHz, it is likely that even 20 MHz will still work, as every vendor has certain tolerances in their "max." specification values.
    However, using higher speeds than 10 MHz on the JTAG interface is simply out of spec.
    It is like configuring the PLL in the MCU for 200 MHz if only 168 MHz are specified:
    You won't get any error and it is likely that the 200 MHz will still work but you do not know how stable they are and if they work if the temperature goes up etc.

    Right now, we only have an artificial upper limit for some very few MCUs that are known to be working with max. xxx.
    However, the STM32F103VET6 is none of these devices.
    So you won't get any error message etc. from J-Link when selecting 15 MHz while the datasheet of the MCU may say max. 10 MHz.


    BR
    Alex
    Please read the forum rules before posting.

    Keep in mind, this is *not* a support forum.
    Our engineers will try to answer your questions between their projects if possible but this can be delayed by longer periods of time.
    Should you be entitled to support you can contact us via our support system: segger.com/ticket/
    Or you can contact us via e-mail.