Intel E3815 FH8065301567411 Data Sheet
Product codes
FH8065301567411
Register Access Methods
Intel
®
Atom™ Processor E3800 Product Family
Datasheet
63
3
Register Access Methods
There are six different common register access methods:
•
•
•
•
•
(Indirect - via Memory or IO registers)
•
(Indirect - via PCI Configuration Registers)
3.1
Fixed IO Register Access
Fixed IO registers are accessed by specifying their 16-bit address in a PORT IN and/or
PORT OUT transaction from the CPU core. This allows direct manipulation of the
registers. Fixed IO registers are unmovable register in IO space.
PORT OUT transaction from the CPU core. This allows direct manipulation of the
registers. Fixed IO registers are unmovable register in IO space.
3.2
Fixed Memory Mapped Register Access
Fixed Memory Mapped IO (MMIO) registers are accessed by specifying their 32/36-bit
address in a memory transaction from the CPU core. This allows direct manipulation of
the registers. Fixed MMIO registers are unmovable registers in memory space.
address in a memory transaction from the CPU core. This allows direct manipulation of
the registers. Fixed MMIO registers are unmovable registers in memory space.
3.3
IO Referenced Register Access
IO referenced registers use programmable base address registers (BARs) to select a
range of IO addresses that it will use to decode PORT IN and/or PORT OUT transactions
from the CPU to directly access a register. Thus, the IO BARs act as pointers to blocks
of actual IO registers. To access an IO referenced register for a specific IO base
address, start with that base address and add the register’s offset. Example pseudo
code for an IO referenced register read is shown below:
range of IO addresses that it will use to decode PORT IN and/or PORT OUT transactions
from the CPU to directly access a register. Thus, the IO BARs act as pointers to blocks
of actual IO registers. To access an IO referenced register for a specific IO base
address, start with that base address and add the register’s offset. Example pseudo
code for an IO referenced register read is shown below:
Register_Snapshot = IOREAD([IO_BAR]+Register_Offset)
Table 32. Fixed IO Register Access Method Example (P80 Register)
Type:
I/O Register
(Size: 32 bits)
P80:
80h
Table 33. Fixed Memory Mapped Register Access Method Example (IDX Register)
Type:
Memory Mapped I/O Register
(Size: 32 bits)
IDX:
FEC00000h