Module Operation
362
SPNU503C – March 2018
Copyright © 2018, Texas Instruments Incorporated
CPU Compare Module for Cortex-R4F (CCM-R4F)
Table 9-2. Compare Mismatch Test Sequence
CPU 1 Signal Position
CPU 2 Signal Position
Cycle
n
n-1:8
7
6
5
4
3
2
1
0
n
n-1:8
7
6
5
4
3
2
1
0
1
1
1s
1
1
1
1
1
1
1
1
1
1
1s
1
1
1
1
1
1
1
0
0
1
1
1s
1
1
1
1
1
1
1
1
1
1
1s
1
1
1
1
1
1
0
1
1
1
1
1s
1
1
1
1
1
1
1
1
1
1
1s
1
1
1
1
1
0
1
1
2
1
1
1s
1
1
1
1
1
1
1
1
1
1
1s
1
1
1
1
0
1
1
1
3
::
1
1
1s
1
1
1
1
1
1
1
1
1
0
1s
1
1
1
1
1
1
1
1
n-1
1
1
1s
1
1
1
1
1
1
1
1
0
1
1s
1
1
1
1
1
1
1
1
n
1
1
1s
1
1
1
1
1
1
1
0
1
1
1s
1
1
1
1
1
1
1
1
n+1
1
1
1s
1
1
1
1
1
1
0
1
1
1
1s
1
1
1
1
1
1
1
1
n+2
1
1
1s
1
1
1
1
1
0
1
1
1
1
1s
1
1
1
1
1
1
1
1
n+3
1
1
1s
1
1
1
1
0
1
1
1
1
1
1s
1
1
1
1
1
1
1
1
n+4
::
1
0
1s
1
1
1
1
1
1
1
1
1
1
1s
1
1
1
1
1
1
1
1
2n-1
0
1
1s
1
1
1
1
1
1
1
1
1
1
1s
1
1
1
1
1
1
1
1
2n
9.3.3 Error Forcing Mode
In error forcing mode, a test pattern is applied to the CPU related inputs of the CCM-R4F compare logic to
force an error in the compare error output signal of the compare unit. The ESM error flag “CCM-R4F -
compare” is expected after the error forcing mode completes. As a side effect, the “CCM-R4F self-test
error” flag is also asserted whenever the CPU compare error is asserted.
Error forcing mode is similar to the Compare Mismatch Test operation of self-test mode in which an un-
equal vector is applied to the CCM-R4F CPU signal ports. The error forcing mode forces the compare
mismatch to actually assert the compare error output signal. This ensures that faults in the path between
CCM-R4F and ESM is detected.
Only one hardcoded test pattern is applied into CCM-R4F during error forcing mode. A repeated 0x5
pattern is applied to CPU1 signal port of CCM-R4F input while a repeated 0xA pattern is applied to the
CPU2 signal port of CCM-R4F input. The error forcing mode takes one cycle to complete. Hence, the
failing signature is presented for one clock cycle. After that, the mode is automatically switched to lock
step mode. The key register (MKEY) will indicate the lock step key mode once it is switched to lock step
mode. During the one cycle required by the error forcing test, the CPU output signals are not compared.
User should expect the ESM to trigger a response (report the CCM-R4F fail). If no error is detected by
ESM, then a hardware fault is present.
9.3.4 Self-Test Error Forcing Mode
In self-test error forcing mode, an error is forced at the self-test error signal. The compare unit is still
running in lockstep mode and the key is switched to lockstep after one clock cycle. The ESM error flag
“CCM-R4F - self-test” is expected after the self-test error forcing mode completes. Once the expected
errors are seen, the application can clean the error through ESM module.