SAM4L Datasheet, PDF (268/1185 Pages) ATMEL Corporation – ATSAM ARM-based Flash MCU

ATSAM4L4/L2
14.6
Flash Commands
The FLASHCALW offers a command set to manage programming of the flash memory, locking
and unlocking of regions, and full flash erasing. See Section 14.10.2 for a complete list of
commands.
To run a command, the CMD field in the Flash Command Register (FCMD) has to be written
with the command number. As soon as the FCMD register is written, the FRDY bit in the Flash
Status Register (FSR) is automatically cleared. Once the current command is complete, the
FSR.FRDY bit is automatically set. If an interrupt has been enabled by writing a one to
FCR.FRDY, the interrupt request line of the Flash Controller is activated. All flash commands
except for Quick Page Read (QPR) and Quick User Page Read (QPRUP) will generate an inter-
rupt request upon completion if FCR.FRDY is one.
Any HSB bus transfers attempting to read flash memory when the FLASHCALW is busy execut-
ing a flash command will be stalled, and allowed to continue when the flash command is
complete.
After a command has been written to FCMD, the programming algorithm should wait until the
command has been executed before attempting to read instructions or data from the flash or
writing to the page buffer, as the flash will be busy. The waiting can be performed either by poll-
ing the Flash Status Register (FSR) or by waiting for the flash ready interrupt. The command
written to FCMD is initiated on the first clock cycle where the HSB bus interface in FLASHCALW
is IDLE. The user must make sure that the access pattern to the FLASHCALW HSB interface
contains an IDLE cycle so that the command is allowed to start. Make sure that no bus masters
such as DMA controllers are performing endless burst transfers from the flash. Also, make sure
that the CPU does not perform endless burst transfers from flash. This is done by letting the
CPU enter Power Save mode after writing to FCMD, or by polling FSR for command completion.
This polling will result in an access pattern with IDLE HSB cycles.
All the commands are protected by the same keyword, which has to be written in the eight high-
est bits of the FCMD register. Writing FCMD with data that does not contain the correct key
and/or with an invalid command has no effect on the flash memory; however, the PROGE bit is
set in the Flash Status Register (FSR). This bit is automatically cleared by a read access to the
FSR register.
Writing a command to FCMD while another command is being executed has no effect on the
flash memory; however, the PROGE bit is set in the Flash Status Register (FSR). This bit is
automatically cleared by a read access to the FSR register.
If the current command writes or erases a page in a locked region the command has no effect on
the flash memory; however, the LOCKE bit is set in the FSR register. This bit is automatically
cleared by a read access to the FSR register.
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