Store Framebuffer in OSPI PSRAM?

[DMacD.1]

MCU: STM32L4R9ZIJ6

PSRAM: APS1604M-3SQR-SN

Display: 800x480, RGB888, 24-bit

Hi, I'd like to use the mentioned PSRAM to store the TouchGFX framebuffer using OCTOSPI in QuadSPI mode.

I have tried setting the Frame Buffer Start Address to

OCTOSPI1_BASE (0x90000000), but that does not seem to work. I only get junk data.

I have read the TouchGFX docs, LTDC datasheets, and OSPI datasheets very thoroughly, and still cannot figure it out.

Additional Q's:

1. How does the MCU "know" an external PSRAM has been added?
2. Should I have used FMC for this procedure instead?

Note: I am using a custom board/application. Please assume the hardware is correct for the sake of discussion.

Any help would be appreciated. If any further clarification is needed please ask. I will include an image of the LCD display image as it stands.

[Tesla DeLorean]

>>How does the MCU "know" an external PSRAM has been added?

You'd have BSP code initializing the clocks,pins and OSPI/OSPIM peripheral, bring-up/config memory, enable the memory-mapping.

If you don't initialize it on the MCU, it will Hard Fault

You can validate the memory works via data pattern testing.

[DMacD.1]

Thank you for your response.

I've done the initializing through CubeMX with GPIO pins as such:

// octospi.c    
 
/**OCTOSPI1 GPIO Configuration
    PC11     ------> OCTOSPIM_P1_NCS
    PF8     ------> OCTOSPIM_P1_IO0
    PF6     ------> OCTOSPIM_P1_IO3
    PF7     ------> OCTOSPIM_P1_IO2
    PF10     ------> OCTOSPIM_P1_CLK
    PF9     ------> OCTOSPIM_P1_IO1
    */

Is there anything further I need to do?(Outside of the MX generated code)

I have tried the APS1604M-3SQR-SN example code on pg.57 of AN5050, but found nothing written to 0x90000000 upon inspection in the CubeIDE Memory Monitor.

[Tesla DeLorean]

I'm not familiar with your design/implementation.

If this is a custom design you'll likely have to do some validation

[DMacD.1]

No worries. It is a custom design. I'm looking for software answers and assuming the hardware is correct. If all I need to do is setup OSPI in CubeMX then write to address 0x90000000 then that answers my question to a degree. Thank you.

[DMacD.1]

It seems I'm having an issue between OSPI indirect mode and memory mapped mode. Memory mapped mode is read-only and likely works better for Flash memory, where Images and other TouchGFX things are stored. I am trying to use memory mapped mode to read the frame buffer, but since it is read only OSPI cannot "store" or write the frame buffer to the OSPI address 0x90000000.

I will try using indirect mode instead.

[Tesla DeLorean]

I'm not sure this L4+ device supports memory mapped read/write to RAM on the OctoSPI, read perhaps, write don't think so.

For DMA/LTDC operation it's going to need to be memory-mapped for those to read data.

The memory-mapped and command modes aren't exactly inter-operable.

The general expectation being that the display/frame buffer is within the internal SRAM, so that it's not constantly switching modes, and disturbing the painting of images onto the screen.

[Alex - APMemory]

There are limitation with the STM32L4R... to use OPI & QSPI RAM.

This is solved with later STM32 (L5, U5, H7...)

Alex