System Reset Conditions

External POR

PS_POR_B pin

Deasserted after power up.

Assert at any time with immediate affect.

Resets all logic, RAMs, and registers.

Prepares device for possible secure boot.

•Mode pins sampled.

No

[external_por]

Internal POR

System error

PMU_Global.ERROR_POR_{1,2}.

Same as External POR except:

•ERROR_STATUS_{1, 2} registers unaffected.

No

[internal_por]

External SRST

PS_SRST_B pin⁽²⁾

Device pin that is usually connected to the debugging tool.
Disable RESET_CTRL [srst_dis]

Same as External POR except:
Modes pins not sampled. Several registers unaffected (i.e., require a POR to reset):

•System error enable.

•PMU global persistent.

•CSU_status, ENC_status

•LOC_PWR_STATE (power state).

•RAMs not cleared.

Yes

[srst]

Internal SRST

Register write

CRL_APB.RESET_CTRL [soft_reset].

Same as external SRST.

Yes

[soft]

System error

PMU_GLOBAL.ERROR_SRST_{1,2}.

Same as external SRST.

Yes

[pmu_sys_reset]

Register write

CRL_APB.RST_LPD_TOP [fpd_reset].

Same as external SRST except:

•PL and LPD unaffected.

N/A

Register write

PMU_GLOBAL.GLOBAL_RESET [PS_ONLY_RST].

Same as external SRST except:

•PL and LPD unaffected.

Yes

[psonly_reset_req]

Debug SRST

DAP controller

Arm DAP.

Same as external SRST except the debug logic state is preserved.⁽³⁾

Yes

[debug_sys]

Reset Debugger

DAP controller

BLOCKONLY_RST [debug_only].

Resets the CoreSight debug logic only.

N/A

No change.

Notes:

1.All resets have an immediate effect. Effects are driven by reset edges and levels.

2.The PS_SRST_B pin can be enabled and disabled by writing to the CRL_APB.RESET_CTRL [srst_dis] bit.

3.RPU debug logic is not preserved.