AN4124

FCCU settings

Doc ID 023294 Rev 2

13/32

5

FCCU settings

Normally the FCCU is configured at start up. In any case, it is possible to manage some

registers only in CONFIG state (according to IP Specification Block guide).

5.1

Example 1: FCCU critical fault injection (no NMI assertion)

We show the FCCU functionality by means of an example which uses fault injection (with

fake funtionality), in order to show the FCCU reaction. The example is without NMI

assertion. The fault is checked and cleared by looking in the CFSx registers.

Example description

●

Put FCCU in CONFIG state: set registers

●

Return to NORMAL state by means of a procedure or by allowing timer out to elapse

●

Inject (fake) faults

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After RESET (by RGM), verify, in SAFE state (without NMI), which fault was detected

(FCCU_CFS0 register)

●

Clear the FCCU_CFS0 register (by suitable procedure)

Example procedure

●

After reset the FCCU automatically enters NORMAL state.

●

Configure FCCU in CONFIG with Dual-rail Encoding Protocol.

–

Write the key to the FCCU_CTRLK register [OP1].

–

Write the FCCU_CTRL register (operation OP1).

●

Emulate all (fake) SW/HW faults.

–

FCCU_CFG: (Configuration Register)

–

SM = 1 (EOUT protocol (dual-rail, time-switching) fast switching mode)

–

PS = 1 (fcc_eout[1] active low, fcc_eout[0] active low)

–

FOM = 000 (Fault Output Mode selection = Dual-Rail (default state)

[fccu_eout[1:0] = outputs])

–

FOP=0 (Fault Output Prescaler = Input clock frequency (ipg_clk_safe clock) is

divided by 2048)

●

Enter NORMAL state.

–

Write the key into the FCCU_CTRLK register [OP2].

–

Write the FCCU_CTRL register (operation OP2).

●

Set fault by FCCU_CFF registers (RESET assertion by RGM).

●

Read and verify FCCU_CFS0..3 by means of procedure (NMI was masked).

●

Clear HW/SW faults from FCCU_CFS0..3 by means of procedure.