security reasons, Hot-Plugging is not available when the device is protected by the NVMCTRL security
bit.
This detection requires that pads are correctly powered. Thus, at cold startup, this detection cannot be
done until POR is released. If the device is protected, Cold-Plugging is the only way to detect a debugger
probe, and so the external reset timing must be longer than the POR timing. If external reset is
deasserted before POR release, the user must retry the procedure above until it gets connected to the
device.
Related Links
NVMCTRL – Non-Volatile Memory Controller
on page 515
on page 523
14.7. Chip Erase
Chip-Erase consists of removing all sensitive information stored in the chip and clearing the NVMCTRL
security bit. Therefore, all volatile memories and the Flash memory (including the EEPROM emulation
area) will be erased. The Flash auxiliary rows, including the user row, will not be erased.
When the device is protected, the debugger must reset the device in order to be detected. This ensures
that internal registers are reset after the protected state is removed. The Chip-Erase operation is
triggered by writing a '1' to the Chip-Erase bit in the Control register (CTRL.CE). This command will be
discarded if the DSU is protected by the Peripheral Access Controller (PAC). Once issued, the module
clears volatile memories prior to erasing the Flash array. To ensure that the Chip-Erase operation is
completed, check the Done bit of the Status A register (STATUSA.DONE).
The Chip-Erase operation depends on clocks and power management features that can be altered by the
CPU. For that reason, it is recommended to issue a Chip- Erase after a Cold-Plugging procedure to
ensure that the device is in a known and safe state.
The recommended sequence is as follows:
1.
Issue the Cold-Plugging procedure (refer to
). The device then:
1.1.
Detects the debugger probe.
1.2.
Holds the CPU in reset.
2.
Issue the Chip-Erase command by writing a '1' to CTRL.CE. The device then:
2.1.
Clears the system volatile memories.
2.2.
Erases the whole Flash array (including the EEPROM emulation area, not including
auxiliary rows).
2.3.
Erases the lock row, removing the NVMCTRL security bit protection.
3.
Check for completion by polling STATUSA.DONE (read as one when completed).
4.
Reset the device to let the NVMCTRL update fuses.
14.8. Programming
Programming the Flash or RAM memories is only possible when the device is not protected by the
NVMCTRL security bit. The programming procedure is as follows:
1.
At power up, RESET is driven low by a debugger. The on-chip regulator holds the system in a POR
state until the input supply is above the POR threshold. The system continues to be held in this
static state until the internally regulated supplies have reached a safe operating state.
Atmel SAM L22G / L22J / L22N [DATASHEET]
Atmel-42402E-SAM L22G / L22J / L22N_Datasheet_Complete-07/2016
80