BCM7252 JTAG

Discussion in 'Hardware troubles and Repair support.' started by zOrg, Jun 19, 2017.

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  1. zOrg

    zOrg New Member

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    Hello!

    I have a board for experiments which is based on the same CPU as DM900 (Broadcom BCM7252).

    I followed this thread https://jb8a8f8.com/support/index.p...500hd-i2c-cypress-board-connection-to-bbs.90/ to try to connect to debug port.

    As far as I understand, there is no yet leaked support of this CPU in Broadband Studio.

    However, when I tried to connect to board while BBS configured to some another CPU, I saw activity on I2C bus. Moreover, I saw requests and responses as well.

    What frustrates me, is that this CPU is ARM architecture, so this debug port might be ARM SWD.

    Could anyone help me to understand if JTAG on this board even enabled? How to properly determine its type?

    Some message exchange I grabbed:
    [​IMG]
     
  2. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    Since the dm900uhd/520hd/525hd dreamboxes are pretty new there is not much information about it regarding the special connections.
    But I assume you use now the I2C pins from the connector CN301 (DM520=CN902).

    But there are more connectors as for this box the CN201 10pins, and the CN703 8 pins.
    I've tried to figure out these pins but I'm struggle to figure out were they for and which type ports they are.
    As for the 10 pins it has Ground pins, pin 2 and 9 therefore it seems not to be a swd pinout or other (for me) known pinouts.
    Other pins as 1, 3 till 8 pins has vdc voltages around the 3,3v.

    As for the CN703 8 pins, it has one ground on the pin 8, further some vdc on pins 1,3,6,7.

    In any case, till now I'm not sure which connectors they are with the exeption of the CN301.
     
  3. zOrg

    zOrg New Member

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    On my board the connector I am talking about looks pretty like the CN301. As I see no I2C chips on my board, I am sure this is some kind of debug port. However, I can't guess *which* debug port it is.

    I am also interested in more general understanding of Broadcom-specific debug port (JTAG) that is accessible with EZ-USB. Is there information about it? Some general description, proper naming... Some common words about the protocol. It is interesting to know if this debugging functionality completely disabled or it is just unsupported (yet).


    Technically, this could be SWD pinout :), for instance, see this schematic (small 10-pin port at the top): https://www.olimex.com/Products/ARM/JTAG/ARM-JTAG-SWD/resources/ARM-JTAG-SWD-schematic.pdf
     
  4. Johnny B.

    Johnny B. Technical Support Staff Member Moderator

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    I assume you use the SCL/SDA and ground pin which is I2C (serial communication) and these are directly connected to the cpu, and there are only two resistor to it.

    I2C.png

    And this is the common way for using to debug, and even to access/edit the cpu settings/data (if enabled).
    More about I2C you could read at wiki i2c or google to broadcom I2c debug.
    In any case (I think) you need a (bbs) script for giving some instruction, but I don's have them.

    As for the 10p connector and SWD, I'm not convinced that it is a SWD port, because normally the ground pins for a SWD 10 pins connector it should then be 3/5/8.
    And this connector has only 2 and 9 for the ground.
    I'm not dare to say that it can not be used as a SWD connection, but because these ground pins are different I have some doubts.