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USB Superspeed Peripherals

Anonymous
Not applicable

 Hi,

   

I had read the DVK description as well as the AN76405. Both documents describe that the MISO and MOSI lines in SPI boot mode should not be connected to a pull up resistor. I do not know if it will work when I have connect those pins also to a FPGA I/O? Can anybody tell me a specifically description of the behaviour of MOSI and MISO lines.

   

thanks, 

   

lumpi

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7 Replies
Anonymous
Not applicable

Hi Lumpi,

   

You should be able to connect SPI lines to different slaves with out any issue. In your case, they are FPGA and SPI flash.

   

CS or SS (Slave Select) decides the device that FX3 wants to communicate.

   

Are you seeing any issue regarding this use case.

   

Please let me know.

   

Thanks,

   

sai krishna.

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Anonymous
Not applicable

It's critical to the boot process that there not be a pull-up on MISO. Some FPGAs have internal pull-ups, so you may need to add a strong pull-down in order to boot properly.

Steve

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Anonymous
Not applicable

Clarification: floating MISO is not good either, if your boot flash tri-states that signal.


Steve 

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Anonymous
Not applicable

 Hi Sai Krishna and Steve,

   

thanks a lot for your suggestions we have destined the additional pull down at MISO line in our hardware design.

   

regards,

   

lumpi

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Anonymous
Not applicable
        Hi, now I have new hardware and the SPI boot won't work. That is the case where the SPI MOSI and MISO lines are connected to SPI Flash (M25P32) and to FPGA (PULL UPS). First try was without a pull down at the MISO line. -> FX3 just read out 4 bytes after power up and then usb fallback comes up. Second try with a pull down resistor (1,5kOhm) at the MISO line. -> FX3 is reading out lots of bytes but it never stops to read out. It seems that FX3 can not find a firmware file with correct checksum. I already tried the firmware file on the DVK board that works. But the same firmware file on our own hardware won't work. The difference between our hardware and the FX3 dvk board is just that MISO and MOSI are connected to flash and to FPGA. regards, lumpi   
ManaskantD_51
Employee

 Lumpi,

   

 

   

You can enable the SPI block of FPGA once the firmware gets downloaded into FX3. You can use a GPIO as an interrupt to the FPGA to start the SPI module. In SPI disable mode, the lines should be kept floating,

   

 

   

Thanks,

   

Manas

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Anonymous
Not applicable
        Hi, you have not understood my question or I was not exactly enough. I like to use the BOOT MODE of FX3: SPI, and fallback is USB. So FX3 PMODE Pins are configured to that (SPI, if fails then USB). So I have no code running on FX3 when the issue happens which I described in my last post. regards, lumpi   
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