HD6417751 Datasheet, PDF (98/1105 Pages) Renesas Technology Corp – SuperH RISC engine

• URC: Random counter for indicating the UTLB entry for which replacement is to be
performed with an LDTLB instruction. URC is incremented each time the UTLB is accessed.
When URB > 0, URC is reset to 0 when the condition URC = URB occurs. Also note that, if a
value is written to URC by software which results in the condition URC > URB, incrementing
is first performed in excess of URB until URC = H'3F. URC is not incremented by an LDTLB
instruction.
• SQMD: Store queue mode bit. Specifies the right of access to the store queues.
0: User/privileged access possible
1: Privileged access possible (address error exception in case of user access)
• SV: Bit that switches between single virtual memory mode and multiple virtual memory mode.
0: Multiple virtual memory mode
1: Single virtual memory mode
When this bit is changed, ensure that 1 is also written to the TI bit.
• TI: TLB invalidation bit. Writing 1 to this bit invalidates (clears to 0) all valid UTLB/ITLB
bits. This bit always returns 0 when read.
• AT: Address translation enable bit. Specifies MMU enabling or disabling.
0: MMU disabled
1: MMU enabled
MMU exceptions are not generated when the AT bit is 0. In the case of software that does not
use the MMU, therefore, the AT bit should be cleared to 0.
3.3 Address Space
3.3.1 Physical Address Space
The SH7751 Series supports a 32-bit physical address space, and can access a 4-Gbyte address
space. When the MMUCR.AT bit is cleared to 0 and the MMU is disabled, the address space is
this physical address space. The physical address space is divided into a number of areas, as
shown in figure 3.3. The physical address space is permanently mapped onto 29-bit external
memory space; this correspondence can be implemented by ignoring the upper 3 bits of the
physical address space addresses. In privileged mode, the 4-Gbyte space from the P0 area to the
P4 area can be accessed. In user mode, a 2-Gbyte space in the U0 area can be accessed. Accessing
the P1 to P4 areas (except the store queue area) in user mode will cause an address error.
Rev. 3.0, 04/02, page 58 of 1064