Section 11 Local Bus State Controller (LBSC)
Rev.1.00 Dec. 13, 2005 Page 393 of 1286
REJ09B0158-0100
11.5.8
Wait Cycles between Accesses
A problem associated with higher operating frequencies for external memory buses is that the data
buffer turn-off after completion of a read from a low-speed device may be too slow, causing a
collision with the data in the next access, and resulting in lower reliability or malfunctions. To
prevent this problem, this module provides a data collision prevention function. It stores the
preceding access area and the type of read/write and inserts a wait cycle before the access cycle if
there is a possibility of a bus collision when the next access is started. The process for wait cycle
insertion consists of inserting idle cycles between the access cycles as shown in section 11.4.3,
CSn Bus Control Register (CSnBCR). If bits IWW, IWRWD, IWRWS, IWRRD and IWRRS in
CSnBCR (n
=
0 to 2 and 4 to 6) are used to set the number of idle cycles between accesses, the
number of inserted idle cycles is only the specified number of idle cycles minus the number of idle
cycles specified by the bits.
When bus arbitration is performed, the bus is released after wait cycles are inserted between the
cycles.
When a DMA transfer is performed, wait cycles are inserted as set in CSnBCR idle cycle bits.
When access the MPX interface area continuously after read access, 1 wait cycle is inserted even
if set the wait cycle to 0.
When the access size is 8-byte or 16-byte, wait cycles are inserted every 4-byte access.
Содержание SH7780 Series
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Страница 450: ...Section 11 Local Bus State Controller LBSC Rev 1 00 Dec 13 2005 Page 400 of 1286 REJ09B0158 0100 ...
Страница 492: ...Section 12 DDR SDRAM Interface DDRIF Rev 1 00 Dec 13 2005 Page 442 of 1286 REJ09B0158 0100 ...
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Страница 726: ...Section 18 Timer Unit TMU Rev 1 00 Dec 13 2005 Page 676 of 1286 REJ09B0158 0100 ...
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Страница 1104: ...Section 27 NAND Flash Memory Controller FLCTL Rev 1 00 Dec 13 2005 Page 1054 of 1286 REJ09B0158 0100 ...
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