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Code Security Module (CSM)
53
SPRUI07–March 2020
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System Control and Interrupts
To summarize, it is possible to load code onto the unprotected on-chip program SARAM shown in
Table 1-11 via the JTAG connector without any impact from the Code Security Module. The code can be
debugged and the peripheral registers initialized, independent of whether the device is in secure or
unsecure mode.
1.2.3 Incorporating Code Security in User Applications
Code security is typically not required in the development phase of a project; however, security is needed
once a robust code is developed. Before such a code is programmed in the flash memory, a password
should be chosen to secure the device. Once a password is in place, the device is secured (programming
a password at the appropriate locations and either performing a device reset or setting the FORCESEC bit
(CSMSCR.15) is the action that secures the device). From that time on, access to debug the contents of
secure memory by any means (via JTAG, code running off external/on-chip memor, and so on) requires
the supply of a valid password. A password is not needed to run the code out of secure memory (such as
in a typical end-customer usage); however, access to secure memory contents for debug purpose requires
a password.
If the code-security feature is used, any one of the following directives must be used when a function
residing in secure memory calls another function which belongs to a different secure zone or to unsecure
memory:
• Use unsecure memory as stack
• Switch stack to unsecure memory before calling the function
• Unlock security before calling the function
Note that the above directives apply for any address-based-parameters passed on to the called function,
basically making sure that the called function can read/write to these address-based parameters.
(1)
These registers are EALLOW protected. Refer to Section 1.5.2 for more information.
Table 1-12. Code Security Module (CSM) Registers
Memory
Address Register Name Reset Values Register Description
KEY Registers
0x00 - 0AE0 KEY0
(1)
0xFFFF Low word of the 128-bit KEY register
0x00 - 0AE1 KEY1
(1)
0xFFFF Second word of the 128-bit KEY register
0x00 - 0AE2 KEY2
(1)
0xFFFF Third word of the 128-bit KEY register
0x00 - 0AE3 KEY3
(1)
0xFFFF Fourth word of the 128-bit key
0x00 - 0AE4 KEY4
(1)
0xFFFF Fifth word of the 128-bit key
0x00 - 0AE5 KEY5
(1)
0xFFFF Sixth word of the 128-bit key
0x00 - 0AE6 KEY6
(1)
0xFFFF Seventh word of the 128-bit key
0x00 - 0AE7 KEY7
(1)
0xFFFF High word of the 128-bit KEY register
0x00 - 0AEF CSMSCR
(1)
0x005F CSM status and control register
Password Locations (PWL) in Flash Memory - Reserved for the CSM password only
0x33 - FFF8 PWL0 User defined Low word of the 128-bit password
0x33 - FFF9 PWL1 User defined Second word of the 128-bit password
0x33 - FFFA PWL2 User defined Third word of the 128-bit password
0x33 - FFFB PWL3 User defined Fourth word of the 128-bit password
0x33 - FFFC PWL4 User defined Fifth word of the 128-bit password
0x33 - FFFD PWL5 User defined Sixth word of the 128-bit password
0x33 - FFFE PWL6 User defined Seventh word of the 128-bit password
0x33 - FFFF PWL7 User defined High word of the 128-bit password
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