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KurtE / ILI9341_t3n

Extended ILI9341_T3 library (Teensy) including all SPI buses, Frame buffer, plus
MIT License
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Teensy 3.6 vs Teensy 4.0 DMA Speed and frameCount() #20

Closed mr-stivo closed 4 years ago

mr-stivo commented 4 years ago

Hi.

I've recently been working on migrating a project from a Teensy 3.6 to a Teensy 4. I'm noticing the Teensy 3.6 is much faster updating the screen using DMA.

It looks like the SPI clock speed setting for the Teensy 4 is not ignored, but capped at a fairly slow speed. I've tried allowing the library to allocate the frame buffer as well as allocating it myself using DMAMEM.

I'm wondering if anyone else is seeing similar speed differences? Any workarounds?

Thanks in advance for the help.

Arduino 1.8.10 Teensyduino 1.48

Teensy 3.6
240 Mhz

#define ILI9341_SPICLOCK 30000000
frameCount() = 24 fps

#define ILI9341_SPICLOCK 60000000
frameCount() = 45 fps
KurtE commented 4 years ago

Sorry, I don't have too much time to look into this.

If you need higher SPI speeds, then maybe you need to change which clock is used to control SPI. In particular what is the setting for CCM_CBCMR register.

I think by default we choose The second clock:

CCM_CBCMR = (CCM_CBCMR & ~(CCM_CBCMR_LPSPI_PODF_MASK | CCM_CBCMR_LPSPI_CLK_SEL_MASK)) |
        CCM_CBCMR_LPSPI_PODF(6) | CCM_CBCMR_LPSPI_CLK_SEL(2); // pg 714

Actually it is now page 1112... Which from our beginTransaction code looks like it starts off with 528MHZ clock going into SPI subsystem. If you try changing that (2) to (1), or change it after begin is called to (1), then I believe it will feed a 720mhz clock into SPI....

Also need to look at the PODF fields of that as well...

You might ask this types of question on the Forum and maybe will have some time to look again...

mr-stivo commented 4 years ago

Hi Kurt,

I see there was some action in the PJRC forums regarding the SPI speed. Lucky timing for me.

I'm using your modified SPI library and setting #define ILI9341_SPICLOCK 80000000. frameCount() is around 61-62 fps. Very fast.

Thanks for the help and thank you so much for your libraries. I'll ask future questions in the PJRC forums.