MCUXpresso - CAN implementation uses lots of ram

[JK_265]

I have an LP55S16 eval board.  When I use the peripheral tool to configure CAN0, my project no longer builds as the SRAM usage goes to 113% versus 13% without the CAN implementation.  I was expecting to see a 64KB buffer in the implementation, but did not.  Does this have to do with the buffer alignment for CAN, which appears to be on a 64KB boundary?  If so, how do I modify it in the peripheral tool?  Or must I simply tweak a file by hand afterward?

On a related note, why does the linker configuration break things into 3 parts by default?  They are SRAM,USB_RAM, and SRAMX (64 KB, 16KB, and 16KB).  Making USB it's own area makes some sense, but I don't understand why SRAM and SRAMX weren't simply one contiguous space?  Am I going to break any SDK generated code/examples if I start reallocating this?

[JK_265]

So, I see another post for a different part which suggests this is a glitch and fixed in SDK 2.11:
https://community.nxp.com/t5/LPC-Microcontrollers/CAN-base-address-align-restriction-in-LPC55/m-p/13...

Can someone confirm that's true for my part, and comment on the question regarding the default linker configuration?

Thanks.

[xiangjun_rong]

Hi,

Pls refer to the section 41.8.44 Message RAM base address register in UM11295.pdf.

The CAN message buffer requires that the low boundary address must be 0x1_0000, in other words, it is a 64KB block, but obviously, the CAN message does not need 64KB size.

In SDK, the line is used to allocate space for the CAN message buffer

#define CAN_MRBA_BA_SHIFT (16U)

SDK_ALIGN(uint8_t msgRam[MSG_RAM_SIZE], 1U << CAN_MRBA_BA_SHIFT) = {1U};

so the compiler will allocate 64KB space from 0xxxxx_0000 address boundary.

I also pasted the memory map of LPC551x, I think you can use the SRAM_0 as CAN message buiffer, which ranges from 0x2000_0000 0x2000_7FFF, but you do not allocate any variable to SRAM0 in *ld file.

In this way, you can use

CAN0->MRBA=0x2000_0000

it is okay. For the 32KB space, you can use pointer to access the remaining space except for the CAN message buffer.

Hope it can help you