Rev. 1.50, 10/04, page 197 of 448
9.3 Operation
9.3.1
Access from the CPU and FPU
L memory access from the CPU and FPU is direct via the instruction bus and operand bus by
means of the virtual address. As long as there is no conflict on the page, the L memory is accessed
in one cycle.
9.3.2
Access from the SuperHyway Bus Master Module
L memory is always accessed by the SuperHyway bus master module, such as DMAC, via the
SuperHyway bus which is a physical address bus. The same addresses as for the virtual addresses
must be used.
9.3.3 Block
Transfer
High-speed data transfer can be performed through block transfer between the L memory and
external memory without cache utilization.
Data can be transferred from the external memory to the L memory through a prefetch instruction
(PREF). Block transfer from the external memory to the L memory begins when the PREF
instruction is issued to the address in the L memory area in the virtual address space.
Data can be transferred from the L memory to the external memory through a write-back
instruction (OCBWB). Block transfer from the L memory to the external memory begins when the
OCBWB instruction is issued to the address in the L memory area in the virtual address space.
In either case, transfer rate is fixed to 32 bytes. Since the start address is always limited to a 32-
byte boundary, the lower five bits of the address indicated by Rn are ignored, and are always dealt
with as all 0s. In either case, other pages and cache can be accessed during block transfer, but the
CPU will stall if the page which is being transferred is accessed before data transfer ends.
The physical addresses [28:0] of the external memory performing data transfers with the L
memory are specified as follows according to whether the MMU is enabled or disabled.
When MMU is Enabled (MMUCR.AT = 1) and RAMCR.RP = 1:
An address of the L memory
area is specified to the UTLB VPN field, and to the physical address of the transfer source (in the
case of the PREF instruction) or the transfer destination (in the case of the OCBWB instruction) to
the PPN field. The ASID, V, SZ, SH, PR, and D bits have the same meaning as normal address
conversion; however, the C and WT bits have no meaning in this page.
Содержание SuperH SH-4A
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