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linuxmemorylinux-kernelembedded-linuxmemory-mapping
shunty
shunty

Reputation: 375

Application processor memory map

What information is contained in the memory map of application processor? Is it tells which subsystem can access which area of RAM or it means if CPU tries to access an address based on memory map it can be RAM address or a device address? I am referring this documentation
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0515b/CIHIJJJA.html.

Here 0x00_0000_0000 to 0x00_0800_0000 is mapped to the boot region, what does that imply?

Upvotes: 0

Views: 520

Answers (2)

Adrian Cox
Adrian Cox

Reputation: 6334

The style of memory map diagram you've linked to shows how the processor and peripherals will decode physical memory addresses. This is a normal diagram for any System-on-Chip device, though the precise layout will vary. The linked page actually lists which units of the SoC use this memory map for their address decoding, and it includes the ARM and the Mali graphics processor. In a Linux system, much of this information will be passed to the kernel in the device tree. It's important to remember that this tells us nothing about how the operating system chooses to organise the virtual memory addresses.

Interesting regions of this are:

DRAM - these addresses will be passed to the DRAM controller. There is no guarantee that the specific board being used has DRAM at all of that address space. The boot firmware will set up the DRAM controller and pass those details to the operating system.

PCIe - these addresses will be mapped to the PCIe controller, and ultimately to transfers on the PCIe links.

The boot region on this chip by default contains an on-chip boot rom and working space. On this particular chip there's added complexity caused by ARMs TrustZone security architecture, which means that application code loaded after boot may not have access to this region. On the development board it should be possible to override this mapping and boot from external devices.

Upvotes: 1

ikstream
ikstream

Reputation: 448

The memory map contains an layout of the memory of your device. It tells your OS, where the OS can place data and how it is accessed, as some areas may be only accessible in a privileged state. Your boot image will be placed in the boot area.This defines among other things your entry point.

Upvotes: 1

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