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Thread: MMAP an external SPI device on the T4.0

  1. #1

    MMAP an external SPI device on the T4.0

    I am currently experimenting with PSRAM on the Teensy 4.0.

    I finally got an IPS6404 (8MB RAM) working on the SPI2 bus of the Teensy4.0.
    Speed can still be improved but I am not using DMA transfer nor QUAD SPI yet.

    This kind of device is only useful for me if I can MMAP the device to a part of the memory map. I currently have a read() and a write() function that handle the paging/caching into real memory but I would like to be able to use pointers to that memory that I can use from C directly without having to call my read/write function.

    Is there an example on how to do this.
    Is there a memory space that can be used to address 8MB?

  2. #2
    Sorry, cant help with the question, but would like to try out the PSRAM chips. Did you get them from Electrodragon ? if so were there package ok for MSL3 ? I am in the uk and imagine they will take some time to arrive. Also would you mind share the code you have so far ?

    Thanks and Regards

  3. #3
    I bought them at Electrodragon.
    The SMD package 3.3v version.
    I am from Belgium. It took 2-3 weeks.
    I ordered 8 and I got something like twice as much.
    I started to use it for my emulator project ( but I cannot make it work as fast as it should. I made a driver that can cache few pages. It runs roughly half what it should on the T4
    I am not using Quad SPI yet.
    I will publish the 1st emulator using it with pictures later this W-E.

  4. #4
    Many thanks for the info. Just wondering did you have any trouble with Moisture Sensitivity Level ? Did you have to bake them or just careful hand soldering ?

    Great work by the way on your emulators!

  5. #5
    I am not an expert of SMD soldering but I managed to solder it without any problem. I use flux. It helps a lot for me as I don't have specific equipment for SMD. No issue with MSL also.

    The PC engine emulator has been added by the way.
    See code and video at

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