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Éder F. Zulian
2018-07-13 15:57:34 +02:00
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@@ -890,6 +890,12 @@ by four in 4X mode. The maximum number of refresh commands that can be
postponed or pulled-in is affected in the same manner. The number of rows per postponed or pulled-in is affected in the same manner. The number of rows per
refresh command is divided by two and by four in 2X and 4X mode respectively. refresh command is divided by two and by four in 2X and 4X mode respectively.
The nomenclature tREFIx is used to denote the refresh interval which value
changes accordingly to the operation mode, e.g., in 2X mode tREFIx corresponds
to tREFI/2. Similarly tRFCx denotes the refresh cycle time which value changes
accordingly to the operation mode. Nevertheless, the values of tRFCx must be
obtained from memory specifications, estimated, measured, etc.
**Flexible Refresh** **Flexible Refresh**
The feature can be used together with regular refresh, bankwise refresh and The feature can be used together with regular refresh, bankwise refresh and
@@ -898,29 +904,34 @@ with all refresh modes are possible.
**Pull-In Refresh** **Pull-In Refresh**
A pull-in starts when there are no pending requests in the memory controller's A pull-in starts when a refresh is triggered (in a multiple of tREFIx) and
buffer, meaning the memory is in idle state. Therefore, in order to prepare there are no pending requests in the memory controller's buffer. This can be
for possible accesses that might happen in the future, a burst of REF commands done in order to prepare for possible accesses that might happen in the
is initiated. If, at any point, requests start coming in, the burst is future. When a burst of REF commands is initiated a REF command is issued (due
to the current tREFIx) followed by one or more REF commands separated in time
by tRFCx. If, at any point, requests start coming in, the burst is
interrupted, meaning that the maximum amount of time, considering the worst interrupted, meaning that the maximum amount of time, considering the worst
case scenario (a request arrives at the same time a REF was issued), is a case scenario (a request arrives at the same time a REF was issued), is a
refresh cycle time (tRFC). The advantage of pulling-in refreshes is that they refresh cycle time (tRFCx).
will not be issued in the near future (in their actual times), allowing for more
efficient accesses to the memory. The advantage of pulling-in refreshes is that they will not be issued in the
near future, i.e., in their actual times multiples of tREFIx, allowing for
more efficient accesses to the memory.
**Postpone Refresh** **Postpone Refresh**
Similarly, the decision to postpone a refresh is done if by the time of a Similarly, the decision to postpone a refresh is done if by the time of a
refresh due there are pending requests on the buffer. Buffered requests may refresh due (multiple of tREFIx) there are pending requests on the memory
generate row-hits, so postponing refreshes may be beneficial for it avoids controller's buffer. Buffered requests may generate row-hits, so postponing
breaking row-hit sequences what reduces the number of commands (e.g., ACT, refreshes may be beneficial for it avoids breaking row-hit sequences what
PRE) to carry out the memory accesses and improves the overall system reduces the number of commands (e.g., ACT, PRE) to carry out the memory
preformance (accesses that are row-hits consume less time). If the memory is accesses and improves the overall system preformance because accesses that are
idle, in the next refresh interval (tREFI) a burst is issued for the same row-hits consume less time. If the memory is idle, in the next refresh
number of REF commands postponed plus the actual refresh for that tREFI. When interval (tREFIx) a burst is issued for the same number of REF commands
the maximum number of postponed refreshes is reached a burst is issued in the postponed plus the actual refresh for that tREFIx. When the maximum number of
next tREFI despite the memory state (busy or idle). A burst of postponed postponed refreshes is reached a burst is issued in the next tREFIx despite
refreshes cannot be interrupted. the state of the memory controller's buffer (empty or not). A burst of
postponed refreshes cannot be interrupted.
**The Flexible Refresh FSM** **The Flexible Refresh FSM**