LPC1768 how to Reserve 4K of SRAM to store data

Thanks Marc

I think your comment has been helpful, but ... If I understand correctly.

the three LPC1768 SRAM banks are:
On-chip SRAM
0x1000 0000 - 0x1000 7FFF For device with 32 kB of local SRAM.
On-chip SRAM (typically Used for peripheral data)
0x2007 C000 - 0x2007 FFFF AHB SRAM - bank 0 (16 kB)
0x2008 0000 - 0x2008 3FFF AHB SRAM - bank 1 (16 kB)

So, if In Options for Target 'FLASH' in Target Tab, I leave this configuration

in Read / Write Memory Areas

default off-chip Start Size NoInit

default on-chip Start Size NoInit
selectedI RAM1 0x10000000 0x8000 Not Selected
Not Selected IRAM2 0x2007C000 0x4000 Not Selected

both local 32Kb SRAM and 16Kb bank 0 SRAM are treated by the linker, and are sensitive to any local and global variables, and used by the stack and heap. and fully 16Kb bank 1 SRAM would never be used during program execution unless I explicitly choose to access it. That's right?

I do not understand what you mean by the expression
(btw. SRAM At This location is Generally Used peripherals for USB and Ethernet)

Do you mean that if my program use USB or Ethernet, I can not use these memory locations to store my data from, and if so ... How I can use this memory and USB or Ethernet at once?

thanks again

Some actions - like DMA transfers - do care about whith memory block you try to use.
Another thing is that the different RAM blocks can be accessed concurrently since the processor have more than one bridge. So the peripherials can perform DMA transfers without affecting bandwidth of the main RAM.

Hi,

Most emac driver and usb stacks require buffers. Because these communication are fast it's often a good idea to put these buffers in the SRAM.
So for example bank 0 would be for the USB stack and bank 1 for the ethernet driver.

I would store my configuration data in a section of the iRAM myself but there is no rule that says you have too use this setup.

You are correct in your explanation of the linker memory section usage. However the only reason to add a memory section to the target tab is so the linker can use it.

For example I add bank 0 and bank 1 and I change the individual file options for my emac and USB source file to use these locations for RAM.

I'm not sure what you are doing but you may want to consider reserving a section of iRAM that the linker can not use.

TARGET TAB

• RAM1 0x1000 0000 - 0x1000 5FFF (for stack, globals...) NOTE end address!
• RAM2 0x2007 C000 - 0x2007 FFFF (for USB)
• RAM3 0x2008 0000 - 0x2008 3FFF (for ethernet)

Then in your code add a block of memory at 0x10006000 for your data.

Thank you everyone, specially Marc

I was quite clear with the explanation you have given me and meets my needs.

thanks again