请解释一下DDR refresh的过程
时间：12-11
整理：3721RD
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在DDR standard中有下面一些描述
AUTO REFRESH is used during normal operation of the DDR SDRAM and is analogous to CASBE-FORERAS (CBR) refresh in previous DRAM
types. This command is nonpersistent, so it must beissued each time a refresh is required.
The refresh addressing is generated by the internal refresh controller. This makes the address bits ”Don’t Care” during an AUTO REFRESH command. The DDR SDRAM requires AUTO REFRESH cycles at an average periodic interval of tREFI (maximum).
To allow for improved efficiency in scheduling and switching between tasks, some flexibility in the absolute refresh interval is provided. A maximum of eight AUTO REFRESH commands can be posted to any given DDR SDRAM, and the maximum absolute interval between any AUTO REFRESH command and the next AUTO REFRESH command is 8 * tREFI.
我不太清楚为什么要8次的auto refresh command，最大间隔为8 * tREFI。请帮忙解释一下，或者有什么文档做参考。谢谢
AUTO REFRESH is used during normal operation of the DDR SDRAM and is analogous to CASBE-FORERAS (CBR) refresh in previous DRAM
types. This command is nonpersistent, so it must beissued each time a refresh is required.
The refresh addressing is generated by the internal refresh controller. This makes the address bits ”Don’t Care” during an AUTO REFRESH command. The DDR SDRAM requires AUTO REFRESH cycles at an average periodic interval of tREFI (maximum).
To allow for improved efficiency in scheduling and switching between tasks, some flexibility in the absolute refresh interval is provided. A maximum of eight AUTO REFRESH commands can be posted to any given DDR SDRAM, and the maximum absolute interval between any AUTO REFRESH command and the next AUTO REFRESH command is 8 * tREFI.
我不太清楚为什么要8次的auto refresh command，最大间隔为8 * tREFI。请帮忙解释一下，或者有什么文档做参考。谢谢
集中刷新几次，可以实现更长的刷新间隔，从而减轻对数据突发操作的影响。