AN2077 View Datasheet(PDF) - STMicroelectronics
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MFG CO.
'AN2077' PDF : 19 Pages View PDF
EEPROM Emulation with STR71x
3 EMBEDDED APPLICATION ASPECTS
This chapter gives useful information for embedded applications where the STR71x em-
bedded-Flash memory is the only non volatile memory available.
3.1 READING THE FLASH WHILE ERASING OR PROGRAMMING
Depending on which STR71xF variant is used, the entire Flash may not be visible to the CPU
when a Flash bank is erased or programmed. When a given microcontroller does not support
Read-While-Write, the EEPROM emulation software should:
– disable all interrupts: as during erasing and programming, it is not possible to have access
to STR71x interrupt vector table;
– copy a few routines into the RAM: before erasing and programming, a few software rou-
tines shall be copied from the Flash into the on-chip RAM; this should include at least the
routines to generate erasing and programming and the routines which wait for the end of
erasing or programming;
– temporarily disable code protection: if code protection is activated, it should be temporar-
ily disabled before executing the code copied into the on-chip RAM.
To cope with application constraints, users may be obliged to support communication during
the programming/erasing. This requires that:
– more software is copied into the on-chip RAM,
– the software loop, polling the Flash status register, is modified to handle the communication
process,
– the minimum communication handler (used during polling) is not using interrupts,
– program/erase suspend command is used.
3.1.1 Suspend and resume commands
As stand-alone Flash memories, STR71xF embedded-Flash controller supports suspend and
resume commands; this allows the erasing or the programming process to be suspended at
any time and resumed later on.
Once suspend command is completed, STR71xF can access the software routines that may
be needed (ex: communication driver) and that were not relocated to the on-chip RAM.
Note The total time for which the Flash is not available is unchanged but this gives the possibility to sus-
pend the process to run specific routines during Flash erasing or programming (ex: communication
protocol).
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