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Thread: 4.1 latest schematics

  1. #1
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    4.1 latest schematics

    Are the latest schematics with U2 - GD32E230F8 made available anywhere?

  2. #2
    Senior Member PaulStoffregen's Avatar
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    Teensy 4.0 & 4.1 schematics haven't been updated for the U2 chip substitution. Realistically, they probably won't ever get updated. This U2 part is meant to be a temporary change until the original chip is available again in sufficient quantity. And no, you probably can't actually buy GD32E230 anywhere, at least not in the same package we're using on Teensy 4.0 & 4.1, and of course it would come blank and be unusable anyway. But you can still buy the original pre-programmed MKL02Z32 chip from PJRC, at least in moderate quantity. We made the substitution partly because not enough of the original chip was available, and partly so we could keep the remaining original well documented chips available for people making custom PCBs. We (probably) can't ever sell the substitute chip for custom PCBs because its package is slightly different and (as far as I know) no ZIF socket exists for it.

    Such is life during these times of global chip shortages...

  3. #3
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    My goal is to desolder U2 and provide and add SWD capability to the board. Therefore, U2 pinout is important to me.

  4. #4
    Senior Member PaulStoffregen's Avatar
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    Teensy 4.1 uses JTAG, not SWD. It would in theory be done if you solder more wires and use a JTAG adaptor. Just know that SWD can not work.

  5. #5
    Senior Member PaulStoffregen's Avatar
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    If you do attempt this, here are the signal locations you'll need.

    Click image for larger version. 

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    BOOT0 needs to be connected to GND for normal operation.

    PSWITCH needs a low-to-high transition to turn on the 1.15V DC-DC power supply for the CPU.

    MOD controls which JTAG device you access, either ARM debug or standard boundary scan. See the reference manual & datasheet for detail.

  6. #6
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    Quote Originally Posted by PaulStoffregen View Post
    Teensy 4.1 uses JTAG, not SWD. It would in theory be done if you solder more wires and use a JTAG adaptor. Just know that SWD can not work.
    Yes
    - Remove U2
    - Pull-out GPIO_AD_B0_06/JTAG_TMS/SWD_DIO and GPIO_AD_B0_07/JTAG_TCK/SWD_CLK from U2 pins
    - Pull-out 3V3 and GND


    U2 pinout is my only reference how where to find those SWD pins, since RT1062 is BGA.

    Why SWD won't work?

  7. #7
    Senior Member PaulStoffregen's Avatar
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    If you play with JTAG boundary scan, the IMXRT chips have an undocumented bug were weird/wrong things happen if you stay in the various scan states for more than about 8 seconds. Parking in the test-logic-reset or run-test/idle states works fine.

  8. #8
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    Thank you.

    Wish me luck, as the pinout is more challenging to solder than in case of NXP micro - TCK is right next to TMS and in the middle of the row.

  9. #9
    Senior Member PaulStoffregen's Avatar
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    SWD absolutely will not work. All Teensy 4.1 boards are permanently fuse configured for JTAG. NXP did not implement dynamic switch between SWD & JTAG as ARM's documentation says. It will only talk JTAG because the fuse is permanently set to configure for JTAG only.

    See the fuse map documentation in the reference manual if you need more info about this.

  10. #10
    Senior Member PaulStoffregen's Avatar
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    Maybe not the answers you wanted, but hopefully this gives you the info you need to get started, rather then wasting a lot of time on reverse engineering.

  11. #11
    Senior Member PaulStoffregen's Avatar
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    Another gotcha is PSWITCH. It will not work if simply wired to 3.3V. NXP's documentation about this quite misleading. It's not a simple active-high enable. A low to high transition is required (after 3.3V power is stable) to get the DC-DC converter to turn on.

    You can find detailed documentation on the power up sequence on this page. Look for the schematic with buttons to highlight each power up step.

    https://www.pjrc.com/store/ic_mkl02_t4.html

    Once you remove U2, you'll lose step #7-8. Before you can even attempt to use JTAG debug, you'll need to create circuitry to drive PSWITCH to cause the CPU power to turn on.

    Obviously you should only attempt JTAG communication after the CPU power becomes stable.
    Last edited by PaulStoffregen; 09-26-2022 at 11:35 PM. Reason: add link to bootloader chip page with power up sequence

  12. #12
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    Thank you for the very thorough support. Looks like it won't work for us.

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