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Thread: How fast is Teensy 4.1 PSRAM?

  1. #1
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    How fast is Teensy 4.1 PSRAM?

    Quick question-

    Just how fast is the PSRAM on a Teensy 4.1? Basically, I'm trying to figure out if it would be fast enough to store a framebuffer for VGA or not.

    Thanks!

  2. #2
    Senior Member+ defragster's Avatar
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    There are TFT displays in use - see forum - where a DMA frame buffer is used for display update. Higher res where the 512KB of RAM2/DMAMEM isn't big enough.

    It is SPI - posts like this : Support-for-the-ILI9488-on-T3-x-and-beyond

    If the same for VGA transfer rate and size ... that may be out there too ... though not sure if the VGA seen had that feature ...

  3. #3
    Senior Member PaulStoffregen's Avatar
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    The answer really depends on some details, especially the number of bits or bytes per pixel.

    The chip at 88 MHz clock has a bandwidth of about 40 MByte/sec, or about 60 MByte/sec if you increase to the maximum clock speed.

    For VGA, 640 x 480 x 60 Hz = 18.4 Mpixel/sec. So if you store only 8 bits per pixel, it's probably fast enough. If you store 32 bits per pixel, definite not enough.

    But bus latency could also be a serious problem. You'll probably need something like FlexIO to serve as a FIFO for the outgoing data. Might be possible to get it working, but could be quite a challenge.

  4. #4
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    Quote Originally Posted by PaulStoffregen View Post
    The answer really depends on some details, especially the number of bits or bytes per pixel.

    The chip at 88 MHz clock has a bandwidth of about 40 MByte/sec, or about 60 MByte/sec if you increase to the maximum clock speed.

    For VGA, 640 x 480 x 60 Hz = 18.4 Mpixel/sec. So if you store only 8 bits per pixel, it's probably fast enough. If you store 32 bits per pixel, definite not enough.

    But bus latency could also be a serious problem. You'll probably need something like FlexIO to serve as a FIFO for the outgoing data. Might be possible to get it working, but could be quite a challenge.
    Yeah, would definitely be only 8 bits per pixel... Also thinking about going for 640x400 instead of 480. If I do that, then there should be enough regular RAM on the Teensy 4 to make it work.

    I'll look into FlexIO.

    Thanks!

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