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UM10375
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© NXP B.V. 2011. All rights reserved.
User manual
Rev. 3 — 14 June 2011
345 of 368
NXP Semiconductors
UM10375
Chapter 21: LPC13xx Flash memory programming firmware
21.16.5 Flash Module Status Clear register
The FMSTATCLR register is used to clear the signature generation completion flag.
21.17 Flash signature generation
The flash module contains a built-in signature generator. This generator can produce a
128-bit signature from a range of flash memory. A typical usage is to verify the flashed
contents against a calculated signature (e.g. during programming).
The address range for generating a signature must be aligned on flash-word boundaries,
i.e. 128-bit boundaries. Once started, signature generation completes independently.
While signature generation is in progress, the flash memory cannot be accessed for other
purposes, and an attempted read will cause a wait state to be asserted until signature
generation is complete. Code outside of the flash (e.g. internal RAM) can be executed
during signature generation. This can include interrupt services, if the interrupt vector
table is re-mapped to memory other than the flash memory. The code that initiates
signature generation should also be placed outside of the flash memory.
21.17.1 Algorithm and procedure for signature generation
Signature generation
A signature can be generated for any part of the flash contents. The address range to be
used for signature generation is defined by writing the start address to the FMSSTART
register, and the stop address to the FMSSTOP register.
The signature generation is started by writing a ‘1’ to FMSSTOP.MISR_START. Starting
the signature generation is typically combined with defining the stop address, which is
done in another field FMSSTOP.FMSSTOP of the same register.
The time that the signature generation takes is proportional to the address range for which
the signature is generated. Reading of the flash memory for signature generation uses a
self-timed read mechanism and does not depend on any configurable timing settings for
the flash. A safe estimation for the duration of the signature generation is:
Duration = int( (60 / tcy) + 3 ) x (FMSSTOP - FM 1)
When signature generation is triggered via software, the duration is in AHB clock cycles,
and tcy is the time in ns for one AHB clock. The SIG_DONE bit in FMSTAT can be polled
by software to determine when signature generation is complete.
Table 355. Flash Module Status Clear register (FMSTATCLR - 0x0x4003 CFE8) bit description
Bit
Symbol
Description
Reset
value
1:0
-
Reserved, user software should not write ones to reserved
bits. The value read from a reserved bit is not defined.
NA
2
SIG_DONE_CLR
Writing a 1 to this bits clears the signature generation
completion flag (SIG_DONE) in the FMSTAT register.
0
31:3
-
Reserved, user software should not write ones to reserved
bits. The value read from a reserved bit is not defined.
NA