Chapter 10 Memory Subsystem.pdf
Chapter 10 Memory Subsystem.pdf
Chapter 10 Memory Subsystem.pdf
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Public Version<br />
www.ti.com General-Purpose <strong>Memory</strong> Controller<br />
The same applies to successive accesses occurring during Word32 or burst accesses split into successive<br />
single accesses when the single-access mode is used (GPMC_CONFIG1_i[30] READMULTIPLE = 0 or<br />
GPMC_CONFIG1_i[28] WRITEMULTIPLE = 0).<br />
All control signals are kept in their default states during these idle GPMC_FCLK cycles. This prevents<br />
back-to-back accesses to the same chip-select without idle cycles between accesses.<br />
<strong>10</strong>.1.5.4.6.3 Idle Cycles Between Accesses to Different Chip-Select (CYCLE2CYCLEDIFFCSEN,<br />
CYCLE2CYCLEDELAY)<br />
Because of the pipelined behavior of the system, successive accesses to different chip-selects can occur<br />
back-to-back with no idle cycles between accesses. Depending on the control signals (nCS, nADV/ALE,<br />
nBE0/CLE, nOE/RE, nWE) assertion and de-assertion timing parameters and on the IC timing<br />
parameters, some control signals assertion times may overlap between the successive accesses to<br />
different CS. Similarly, some control signals (WE, OE/RE) may not respect required transition times.<br />
To work around the overlapping and to observe the required control-signal transitions, a minimum of<br />
CYCLE2CYCLEDELAY inactive cycles is inserted between the access being initiated to this chip-select<br />
and the previous access ending for a different chip-select. This applies to any type of access (read or<br />
write).<br />
If GPMC_CONFIG6_i[6] CYCLE2CYCLEDIFFCSEN is enabled, the chip-select access is delayed until<br />
CYCLE2CYCLEDELAY cycles have expired since the end of a previous access to a different chip-select.<br />
CYCLE2CYCLEDELAY count starts at CSRDOFFTIME/CSWROFFTIME completion. All control signals<br />
are kept inactive during the idle GPMC_FCLK cycles.<br />
NOTE: CYCLE2CYCLESAMECSEN and CYCLE2CYCLEDIFFCSEN should be set in the<br />
GPMC_CONFIG6_i registers to insert idle cycles between accesses on this chip-select and<br />
after accesses to a different chip-select, respectively.<br />
The CYCLE2CYCLEDELAY delay runs in parallel with the BUSTURNAROUND delay.<br />
BUSTURNAROUND is a timing parameter defined for the ending chip-select access,<br />
whereas CYCLE2CYCLEDELAY is a timing parameter defined for starting chip-select<br />
access. The effective minimum delay between successive accesses is based on the larger<br />
delay timing parameter and on the access type combination, since bus turnaround does not<br />
apply to all access types. See Section <strong>10</strong>.1.5.4.6.1 for more details on bus turnaround.<br />
Table <strong>10</strong>-3 describes the configuration required for idle cycle insertion.<br />
Table <strong>10</strong>-3. Idle Cycle Insertion Configuration<br />
1st BUSTURN Second Chip- Add/Data CYCLE2 CYCLE2 Idle Cycle Insertion<br />
Access AROUND Access Select Multiplexed CYCLE CYCLE Between the Two<br />
Type Timing Type SAMECSEN DIFFCSEN Accesses<br />
Parameter Parameter Parameter<br />
R/W = 0 R/W Any Any 0 x No idle cycles are inserted if the<br />
two accesses are well pipelined.<br />
R > 0 R Same Nonmuxed x 0 No idle cycles are inserted if the<br />
two accesses are well pipelined.<br />
R > 0 R Different Nonmuxed 0 0 BTA cycles are inserted.<br />
R > 0 R/W Any Muxed 0 0 BTA cycles are inserted.<br />
R > 0 W Any Any 0 0 BTA cycles are inserted.<br />
W > 0 R/W Any Any 0 0 No idle cycles are inserted if the<br />
two accesses are well pipelined.<br />
R/W = 0 R/W Same Any 1 x CYCLE2CYCLEDELAY cycles<br />
are inserted.<br />
R/W = 0 R/W Different Any x 1 CYCLE2CYCLEDELAY cycles<br />
are inserted.<br />
SPRUGN4L–May 20<strong>10</strong>–Revised June 2011 <strong>Memory</strong> <strong>Subsystem</strong><br />
Copyright © 20<strong>10</strong>–2011, Texas Instruments Incorporated<br />
2121