Once completed, the calculated CRC32 value can be read out of the Data register. The read value must
be complemented to match standard CRC32 implementations or kept non-inverted if used as starting
point for subsequent CRC32 calculations.
If the device is in protected state by the NVMCTRL security bit, it is only possible to calculate the CRC32
of the whole flash array when operated from the external address space. In most cases, this area will be
the entire onboard non-volatile memory. The Address, Length and Data registers will be forced to
predefined values once the CRC32 operation is started, and values written by the user are ignored. This
allows the user to verify the contents of a protected device.
The actual test is started by writing a '1' in the 32-bit Cyclic Redundancy Check bit of the Control register
(CTRL.CRC). A running CRC32 operation can be canceled by resetting the module (writing '1' to
CTRL.SWRST).
Related Links
NVMCTRL – Non-Volatile Memory Controller
on page 515
on page 523
14.11.3.2. Interpreting the Results
The user should monitor the Status A register. When the operation is completed, STATUSA.DONE is set.
Then the Bus Error bit of the Status A register (STATUSA.BERR) must be read to ensure that no bus
error occurred.
14.11.4. Debug Communication Channels
The Debug Communication Channels (DCCO and DCC1) consist of a pair of registers with associated
handshake logic, accessible by both CPU and debugger even if the device is protected by the NVMCTRL
security bit. The registers can be used to exchange data between the CPU and the debugger, during run
time as well as in debug mode. This enables the user to build a custom debug protocol using only these
registers.
The DCC0 and DCC1 registers are accessible when the protected state is active. When the device is
protected, however, it is not possible to connect a debugger while the CPU is running
(STATUSA.CRSTEXT is not writable and the CPU is held under Reset).
Two Debug Communication Channel status bits in the Status B registers (STATUS.DCCDx) indicate
whether a new value has been written in DCC0 or DCC1. These bits, DCC0D and DCC1D, are located in
the STATUSB registers. They are automatically set on write and cleared on read.
Note:
The DCC0 and DCC1 registers are shared with the on-board memory testing logic (MBIST).
Accordingly, DCC0 and DCC1 must not be used while performing MBIST operations.
Related Links
NVMCTRL – Non-Volatile Memory Controller
on page 515
on page 523
14.11.5. Testing of On-Board Memories MBIST
The DSU implements a feature for automatic testing of memory also known as MBIST (memory built-in
self test). This is primarily intended for production test of on-board memories. MBIST cannot be operated
from the external address range when the device is protected by the NVMCTRL security bit. If an MBIST
command is issued when the device is protected, a protection error is reported in the Protection Error bit
in the Status A register (STATUSA.PERR).
1.
Algorithm
The algorithm used for testing is a type of March algorithm called "March LR". This algorithm is able
to detect a wide range of memory defects, while still keeping a linear run time. The algorithm is:
Atmel SAM L22G / L22J / L22N [DATASHEET]
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