Difference between revisions of "ETRA SOM/ETRA Hardware/Power and Reset/Reset scheme and control signals"

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(WIP)
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[[File:ETRA-reset-scheme.png | 800px]]
 
[[File:ETRA-reset-scheme.png | 800px]]
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''TBD: qui di seguito vanno inserite le sezioni che includano la descrizione dei segnali coinvolti nella fase di Reset, ad esempio:''
 
−
 
−
* MRST
 
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* POR
 
−
* SNVS
 
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* SYSRST
 
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* ...
 
−
 
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'''TBD: indicare le connessioni del segnale di reset verso altri device interni (come per esempio la NOR SPI'''
 
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''TBD: di seguito la pagina di AXEL Lite da rivedere nel caso di altri SOM''
 
  
 
=== VDD ===
 
=== VDD ===
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=== NRST ===
 
=== NRST ===
−
Rest signal, tie to DGND to reset the system. It is driven by the PMIC to set the CPU in reset state.
+
Open drain rest signal, tie to DGND to reset the system.
 +
 
 +
It is driven by:
 +
* the PMIC to force the CPU in reset state
 +
* the CPU over a soft reset to restart the application
 +
This signal is also used to reset the following on board peripherals:
 +
* SPI NOR
 +
* eMMC
  
 
=== SOM_PGOOD ===
 
=== SOM_PGOOD ===
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=== PWR_ON ===
 
=== PWR_ON ===
 +
Power on CPU output signal, The state of this signal depends on power state of the processor.
  
 
=== PDR_ON ===
 
=== PDR_ON ===
 +
Input pin that disables the VDD internal voltage monitor. When this signal is set to logic 1 the processor does not issue a reset cycle when the VDD goes below the VVD_OK threshold.
 +
 +
Driven by default by PMIC, internally used for deep sleep modes.
  
 
=== PDR_ON_CORE ===
 
=== PDR_ON_CORE ===
 +
Input pin that disables the VDD_CORE internal voltage monitor. When this signal is set to logic 1 the processor does not issue a core reset cycle when the VDD_CORE goes below the VVD_OK threshold.
 +
 +
Driven by default by PMIC, internally used for deep sleep modes.
  
 
=== PWR_LP ===
 
=== PWR_LP ===
  
−
=== PMIC_VSNVS ===
+
CPU low power mode output, internally used by the PMIC to check the CPU low power state.
−
Some signals that are related to reset circuitry are pulled-up to PMIC_VSNVS. This voltage is generated by PMIC PF0100's VSNVS LDO/Switch and its actual value depends on:
 
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* voltage applied to PMICS's VIN pin
 
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** in case of AxelLite this pin is connected to 3.3VIN power rail
 
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* voltage applied to PMICS's LICELL pin
 
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** in case of AxelLite this pin is connected to pin 14 of SODIMM connector (PMIC_LICELL)
 
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* PMIC's VSNVSCTL register configuration.
 
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Hence '''it is recommended that system designer takes into account these factors in order to properly manage these signals at carrier board level'''.
 
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For more details please refer to section ''VSNVS LDO/Switch'' of ''MMPF0100 Advance Information'' document.
 
−
 
 
−
=== CPU_PORn ===
 
−
 
 
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The following devices can assert this active-low signal:
 
−
* PMIC
 
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* multiple-voltage monitor: this device monitors critical power voltages and triggers a reset pulse in case any of these exhibits a brownout condition
 
−
 
 
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Since SPI NOR flash can be used as boot device, CPU_PORn is connected to this device too. This guarantees it is in a known state when reset signal is released.
 
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−
 
 
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=== Handling CPU-initiated software reset ===
 
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'''By default, MX6 processor does not assert any external signal when it initiates a software reset sequence. Also default software reset implementation does not guarantee that all processor registers are reset properly'''.
 
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For these reasons, it is strongly recommended to use a different approach that, in combination with the use of a processor's watchdog timer (WDT), provides a full hardware reset in case a software reset is issued.
 
  
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This technique is implemented in [[DESK-ETRA-L]]. At software level, U-Boot and Linux kernel software reset routines make use of processor's WDT #2 to assert the WDOG2_B reset signal. This signal in turn is routed to GPIO_1 pad (MUX mode = 1). At hardware level, this signal is AC-coupled to a 3-state output buffer (please refer to U22 chip of [[AxelEVB-Lite]] carrier board), driving PMIC_PWRON.
+
=== WAKEUP ===
 +
PMIC power on signal from CPU, used in low power mode by the CPU internal RTC to restart the PMIC.
  
 
----
 
----
  
 
[[Category:ETRA]]
 
[[Category:ETRA]]

Revision as of 07:36, 30 December 2020

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Reset scheme and control signals[edit | edit source]

The following picture shows the simplified block diagram of reset scheme and voltage monitoring.

ETRA-reset-scheme.png

VDD[edit | edit source]

Some signals that are related to reset circuitry are pulled-up to VDD rail. This voltage is generated by the PMIC and act as power good to switch on/off the all the peripheral that could back power the CPU.

NRST[edit | edit source]

Open drain rest signal, tie to DGND to reset the system.

It is driven by:

  • the PMIC to force the CPU in reset state
  • the CPU over a soft reset to restart the application

This signal is also used to reset the following on board peripherals:

  • SPI NOR
  • eMMC

SOM_PGOOD[edit | edit source]

This is a convencional signal to drive DC/DC enable inputs or switch on/off control signals. It is connected to the VDD through a 22Ohm resistor.

PONKEYn[edit | edit source]

User power on key (active low with internal pull-up), used to wake up the sysytem from power down.

NRST_CORE[edit | edit source]

Reset signal for the core, to be used if the VDD_CORE is not disabled during the reset. Internally tied to NRST signal.

PWR_ON[edit | edit source]

Power on CPU output signal, The state of this signal depends on power state of the processor.

PDR_ON[edit | edit source]

Input pin that disables the VDD internal voltage monitor. When this signal is set to logic 1 the processor does not issue a reset cycle when the VDD goes below the VVD_OK threshold.

Driven by default by PMIC, internally used for deep sleep modes.

PDR_ON_CORE[edit | edit source]

Input pin that disables the VDD_CORE internal voltage monitor. When this signal is set to logic 1 the processor does not issue a core reset cycle when the VDD_CORE goes below the VVD_OK threshold.

Driven by default by PMIC, internally used for deep sleep modes.

PWR_LP[edit | edit source]

CPU low power mode output, internally used by the PMIC to check the CPU low power state.

WAKEUP[edit | edit source]

PMIC power on signal from CPU, used in low power mode by the CPU internal RTC to restart the PMIC.

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