Can't write to external SDRAM address 0xD0000000, only 0xD0000002

[aro]

This code doesn't write anything:

*(__IO uint16_t*) 0xD0000000 = (uint16_t) 0x01;

However, this code does write:

*(__IO uint16_t*) 0xD0000002 = (uint16_t) 0x01;

As you can see, the only difference is the 2 vs 0 at the end. The 0xD0000000 address is defined in the .ioc settings and in the .ld. 

What can this be? Where am I going wrong?

[SKEnbio]

Hi,

Please send more information about Your project. Please check also for other address. Maybe You have problem with physically connection to the external SDRAM. Please see this guide: https://support.touchgfx.com/docs/development/board-bring-up/how-to/04-enable-external-ram 

Best Regards,

Slawek

[jiangfan]

some points to check:

- what board used ? your own board or board from ST ? Are you sure your board works fine ?

- any debug with scope to check the corresponding signals ? like address and data signals ?

[aro]

It's a display connected to a Waveshare board. I had already done the setup that the link suggests.

Sure, the hardware could be an issue. I didn't attempt to debug with the scope yet.

I run this code to test:

uint16_t sdrambuf[SDRAM_BUFFER_SIZE] __attribute__ ((section(".sdram")));

for (counter = 0x00; counter < (SDRAM_SIZE); counter++) {
    sdrambuf[counter] = (uint16_t) counter;
}

You can see in the memory that it first writes 00010001. The variable 'counter' is zero on the first iteration, so I don't know why it writes that. 

The second thing is that first it writes 00000003 and then 00040003. I thought it would be 00030004.

[jiangfan]

You mentioned "It's a display connected to a Waveshare board."

it is confusing. it seems that Waveshare board has MCU STM32H7 on it. but what is the relationship between SDRAM and display ? You would access SDRAM and it is on the display (connected to a Waveshare board) ?

or You would access display (connected to a Waveshare board) and the display using SDRAM address ?

[aro]

The SDRAM is on the board and I use that to connect to the display.

https://www.waveshare.com/openh743i-c-package-a.htm

[aro]

I finally got it to work by simply copying and pasting the board vendor sdram initialization code.

What is strange and I haven't found the reason yes is how it writes to memory: 00030002 00050004 etc. The endianness in the memory region is set to default.

It doesn't really matter for what I do, but it is annoying not to understand what's happening.