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Module Operation
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SPNU563A–March 2018
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Copyright © 2018, Texas Instruments Incorporated
CPU Compare Module for Cortex-R5F (CCM-R5F)
13.2.1.3 Error Forcing Mode
In error forcing mode, a test pattern is applied to the CPU / VIM related inputs of the CCM-R5F compare
logic to force an error in the compare error output signal of the compare unit. Depending if error forcing
mode is applied to the CPU Output Compare Diagnostic or VIM Output Compare Diagnostic, the ESM
error flag “CCM-R5F - CPU compare” or “CCM-R5F - VIM compare” is expected after the error forcing
mode completes. As a side effect, the “CCM-R5F 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-R5F CPU signal ports. The error forcing mode forces the compare
mismatch to actually assert the compare error output signal. This ensures that a fault in the path between
CCM-R5F and ESM is detected.
Only one hardcoded test pattern is applied into CCM-R5F during error forcing mode. A repeated 0x5
pattern is applied to CPU1 / VIM1 signal port of CCM-R5F input while a repeated 0xA pattern is applied to
the CPU2 / VIM2 signal port of CCM-R5F 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 lockstep mode. The key register (MKEY1 for CPU output compare and MKEY2 for VIM output compare)
will indicate the lockstep key mode once it is switched to lockstep mode. During the one cycle required by
the error forcing test, the CPU / VIM output signals are not compared. The user should expect the ESM to
trigger a response (report the CCM-R5F fail). If no error is detected by the ESM, then a hardware fault is
present.
13.2.1.4 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-R5F - 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 the ESM module.
Table 13-3 shows what error signals and flags are asserted in different operating mode. The behavior of
different modes in this table for CPU compare is also valid for other diagnostics such as VIM compare,
Checker CPU Inactivity Monitor and Power Domain monitor.
Table 13-3. Error Flags and Error Signals Generation in Each Mode
Mode Key
Self Test
Error Signal
Compare
Error Signal
CMPE STC STET STE
Active
Compare
Lockstep
0000 Enabled Enabled Enabled Disabled Disabled Disabled
Self-Test 0110 Enabled Disabled Disabled Enabled Enabled Enabled
Error Forcing 1001 Error Error Disabled Disabled Disabled Disabled
Self-Test
Error Forcing
1111 Error Enabled Enabled Disabled Disabled Disabled
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