SH7721 datasheet(860/1524 Pages) RENESAS

860 / 1524 page

Section 24

USB Host Controller (USBH)

Rev. 3.00 Jan. 18, 2008 Page 798 of 1458

REJ09B0033-0300

24.4

Data Storage Format which Required by USB Host Controller

24.4.1

Storage Format of the Transferred Data

USB Host Controller expects that data is compiled from lower address to upper address regardless

endian setting of the CPU. Below figure shows data read operation, which is done by USB Host

Controller.

Program

Memory (Area 3)

USB host

DATA.L

H'11223344

DATA.L

H'55667788

DATA.L

H'00000099

LW read H'11223344

LW read H'55667788

LW read H'00000099

+11

+10

The correspondence between data in memory and data read by USB Host Controller must be

equal. When USB Host Controller reads data from external memory, USB Host Controller reads

data by long word read operation every time regardless of endian. USB Host Controller uses data

in byte from lower address in long word which it reads regardless the endian mode. Even endian

mode is set as big or little, set the data from down addresses.

Below program flow is the example of failure.

• In program, set transfer address A to register R0 at big endian

In program, "MOV.B #H'12,@R0"

• In program, set transfer start address A to USB Host Controller, and set 1byte as transfer size.

Memory

Data expected to be transferred

Actually transferred data

LW read H'12000000

This example shows above operation transfers expected data #H'12.

Data is filled from the lower bits of the memory in writing so that the data is read/written in bi-

direction consistently regardless of the endian type. That is, the data is always aligned with the

little endian specification.

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