Allocating memory for 2x256KB buffer

[dbilancione]

Posted on August 01, 2013 at 16:01

dear all,

I trust you are well. I cannot figure this out and I was hoping someone more experienced than me could help me out...

I am trying to allocate memory for 2 buffers (of uint16_t type) on a STM32F407ZG. each buffer should be max 256KB but I can only allocate 1/10 of that (i.e. 25600x16). I am sure I am missing something but do not know what. Any idea?

Thank you

#memory #stm32f407zg

[Tesla DeLorean]

Posted on August 01, 2013 at 16:56

Allocating with what, and from where?

[dbilancione]

Posted on August 01, 2013 at 17:46

hey clive. using calloc(256000, sizeof(uint16_t)). from anywhere I could. I cannot use an external SRAM as I need the FSMC as I have an LCD.

cheers

[Tesla DeLorean]

Posted on August 01, 2013 at 17:54

Well you'd need to provide >512KB of heap to do that, configuration would depend on the chain, and the allocator implementation. The bigger issue is where that memory would come from, as you don't have that much RAM.

Not sure a fixed buffer from FLASH is what you have in mind.

Some of the

http://www.solomon-systech.com/en/product/mobile-system/standard-display-controller/ssd1962/

controllers have 1.2MB of on-board frame buffer for that purpose.

[dbilancione]

Posted on August 01, 2013 at 18:23

that's what I was thinking but I can't figure out how to configure the heap memory in GCC. but you're saying that I don't have that much RAM so there is no point in increasing the heap.

The LCD I am using has indeed a Solomon controller (SSD1963) but I didn't need the memory for that but to store 2.5sec of audio. If the FSMC is configured for the LCD I cannot use the 512Kx16 SRAM module I have, right?

[Tesla DeLorean]

Posted on August 01, 2013 at 18:47

The FSMC has multiple chip selects to permit multiple devices/banks at 0x60000000, 0x64000000, etc.

Have you reviewed a schematic for the STM3240G-EVAL board?

[dbilancione]

Posted on August 01, 2013 at 19:02

yes, but my understanding was that using the SRAM the Bank1 would have been busy with the memory. So it is possible to use (let's say) PSRAM1 for the LCD and PSRAM2 for the memory, as the pins configuration should be compatible.

[Tesla DeLorean]

Posted on August 01, 2013 at 22:14

I don't know what you mean by busy, the FSMC is an external bus interface, it's utilization will depend on the activity sent it's way. Each bus access will take some arbitrary number of cycles, depending on how it's configured.

I'm looking at a design right now that has

SRAM BANK1 REGION3 0x68000000

NOR BANK1 REGION2 0x64000000

LCD BANK1 REGION4 0x6C000000

NAND BANK3 0x80000000

[dbilancione]

Posted on August 01, 2013 at 23:49

sorry for the stupid question. my bad. I thought all regions of BANK1 would have been used for the SRAM. I had the LCD using REGION4 of BANK1 and now I have added the SRAM module, enabled on REGION3 and it's working!

thank you ever so much clive!