Hardware Reference
In-Depth Information
Model B
Model A
Committed_AS
215,104 KB
57,876 KB
VmallocTotal
This represents the total amount of allocated virtual memory address space.
Model B
Model A
VmallocTotal
188,416 KB
188,416 KB
VmallocUsed
This is the amount of virtual memory that is in use, reported in kilobytes.
Model B
Model A
VmallocUsed
744 KB
704 KB
VmallocChunk
This value reports the largest size of a
vmalloc
area, in kilobytes.
Model B
Model A
VmallocChunk
186,852 KB
186,852 KB
Physical Memory
Let's now turn our attention to the Raspberry Pi's physical memory layout. Normally,
physical memory isn't a concern to application programmers, because the operating
system and its drivers provide an abstract and often portable way to access them.
However, when this support is absent, direct access to a peripheral like the PWM
controller is necessary.
Figure
4-1
illustrates the physical addressing used on the Raspberry Pi. The SDRAM
starts at physical address zero and works up to the ARM/GPU split point (Chapter 2 of
Raspberry Pi System Software Reference
[Apress, 2014] defines the split point). The ARM
peripherals are mapped to physical memory starting at the address of 0x20000000. This
starting address is of keen interest to Pi programmers.
