HD6417706 Datasheet, PDF (102/709 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer Super RISC engine Family/SH7700 Series

Address Space Identifier (ASID): In multiple virtual memory mode, the address space identifier
(ASID) is used to differentiate between processes running in parallel and sharing virtual address
space. The ASID is 8 bits in length and can be set by software setting of the ASID of the currently
running process in page table entry register high (PTEH) within the MMU. When the process is
switched using the ASID, the TLB does not have to be purged.
In single virtual memory mode, the ASID is used to provide memory protection for processes
running simulataneously and using the virtual address space exclusively.
3.2 Register Description
There are five registers for MMU processing. These are located in address space area P4 and can
only be accessed from privileged mode by specifying the address.
These registers for MMU processing are shown below. Refer to section 23, List of Registers, for
more details of the addresses and access sizes.
• Page table entry register high (PTEH)
• Page table entry register low (PTEL)
• Translation table base register (TTB)
• TLB exception address register (TEA)
• MMU control register (MMUCR)
3.2.1 Page Table Entry Register High (PTEH)
The page table entry register high (PTEH) consists of a virtual page number (VPN) and ASID.
The VPN is set the VPN of the virtual address at which the exception is generated in case of an
MMU exception or CPU address error exception. When the page size is 4 kbytes, the VPN is the
upper 20 bits of the virtual address, but in this case the upper 22 bits of the virtual address are set.
The VPN can also be modified by software. As the ASID, software sets the number of the
currently executing process. The VPN and ASID are recorded in the TLB by the LDTLB
instruction.
Bit
31 to 10
9, 8
7 to 0
Bit Name
VPN

ASID
Initial Value R/W

R/W
All 0
R

R/W
Description
Virtual page number
Reserved
These bits are always read as 0. The write value
should always be 0.
Address space identifier
Rev. 4.00, 03/04, page 56 of 660