TC1784
Program Memory Unit (PMU)
User´s Manual
5-91
V1.1, 2011-05
PMU, V1.47
5.6.7.4
Reset Control
The PMU-part of Flash module (FIM) uses
•
the application reset (“class 3 reset”), which may include all reset sources (power-on,
HW, SW and watchdog reset, if configured), and
•
the power-on reset.
If not otherwise stated, always the application/class 3 reset is used.
The flash will be automatically reset to the read mode after every reset.
Resets During Flash Operation
A reset or power failure during an ongoing Flash operation (i.e. program or erase) must
be considered as violation of stable operating conditions. However the Flash was
designed to prevent damage to non-addressed Flash ranges when the reset is applied
as defined in the data sheet. The exceptions are erasing logical sectors and UCBs.
Aborting an erase process of a logical sector can leave the complete physical sector
unreadable. An automatic recovery mechanism is implemented (see next section).
When an UCB erase is aborted the complete Flash can become unusable. There is no
recovery implemented because UCBs are usually only erased in a controlled
environment. The addressed Flash range is left in an undefined state.
When an erase operation is aborted the addressed logical or physical sector can contain
any data. It can even be in a state that doesn’t allow this range to be programmed.
When a page programming operation is aborted the page can still appear as erased (but
contain slightly programmed bits), it can appear as being correctly programmed (but the
data has a lowered retention) or the page contains garbage data. It is also possible that
the read data is instable so that depending on the operating conditions different data is
read.
For the detection of an aborted Flash process the flags FSR.PROG and FSR.ERASE
could be used as indicator but only when the reset was an application reset. Power-on
resets can not be determined from any flags. It is not possible to detect an aborted
operation simply by reading the Flash range. Even the margin reads don’t offer a reliable
indication.
When erasing or programming the PFlash usually an external instance can notice the
reset and simply restart the operation by erasing the Flash range and programming it
again.
However for the case of EEPROM emulation in the DFlash this external instance is not
existing. A common solution is detecting an abort by performing two operations in
sequence and determine after reset from the correctness of the second the
completeness of the first operation.
E.g. after erasing a DFlash sector a page is programmed. After reset the existence of
this page proves that the erase process was performed completely.
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