AM263P4: UniFlash reset

Soft reset its just a core and register reset not mcu reset.

Neil Wilson said:

The only way I can program the board is to try and time a physical reset and click "Load Image"

Niel, Can you share your schematics with me over email.

Hi Neil,

Yes you can find the same in SDK SBL example

Neil Wilson said:

By default, the input path to trigger a warm reset from external pad is disabled. To enable, the TOP_RCM.WARM_RESET_CONFIG.PAD_BYPASS bit should be written 3’b000.

That means that warm reset is not enabled and I need to enable it in software?

Is there an example anywhere on how to provide this enable?

Regards

Neil I understand now:

The external warm reset input path is disabled by default. This is why pressing SW3 on the LP-AM263P or driving WARMRSTn low on your custom board has no effect. You must explicitly enable it via a register write.

Required Configuration

Write 3'b000 to the TOP_RCM.WARM_RESET_CONFIG.PAD_BYPASS field to enable the external pad as a warm reset source 1.

Using the MCU+ SDK, this is done with:

SOC_configureWarmResetSource(SOC_WarmResetSource_PAD_BYPASS);

This call writes the appropriate mask (CSL_TOP_RCM_WARM_RESET_CONFIG_PAD_BYPASS_MASK) to enable the pad input 2.

Why It Doesn't Work Out of the Box

In its power-on-default state, the WARMRSTn pin is configured as an open-drain output (reset status indicator), not an input 3. It requires:

• An external pull-up resistor to VDDS33 (3.3V)
• The PAD_BYPASS register write to enable the input path

No pin mux change is needed—WARMRSTn is a dedicated pin 4.

Timing Considerations

The external warm reset input path is disabled by default. This is why pressing SW3 on the LP-AM263P or driving WARMRSTn low on your custom board has no effect. You must explicitly enable it via a register write.

Required Configuration
Write 3'b000 to the TOP_RCM.WARM_RESET_CONFIG.PAD_BYPASS field to enable the external pad as a warm reset source 1.

Using the MCU+ SDK, this is done with:

SOC_configureWarmResetSource(SOC_WarmResetSource_PAD_BYPASS);
This call writes the appropriate mask (CSL_TOP_RCM_WARM_RESET_CONFIG_PAD_BYPASS_MASK) to enable the pad input 2.

Why It Doesn't Work Out of the Box
In its power-on-default state, the WARMRSTn pin is configured as an open-drain output (reset status indicator), not an input 3. It requires:

An external pull-up resistor to VDDS33 (3.3V)
The PAD_BYPASS register write to enable the input path
No pin mux change is needed—WARMRSTn is a dedicated pin 4.

Timing Considerations
Once enabled, the input signal must remain LOW for at least TOP_RCM.WARM_RSTTIME3 duration to register an assertion, and HIGH for at least TOP_RCM.WARM_RSTTIME2 to register deassertion. These are configurable via SDK functions:

SOC_configureWarmResetInputFallDelay() — sets WARM_RSTTIME3
SOC_configureWarmResetInputRiseDelay() — sets WARM_RSTTIME2
Programmable values range from 500ns to 16.384ms 2.

Board Design Note
If you need both reset input (from a button/external source) and reset status output (to drive peripheral resets), use an open-drain buffer (e.g., SN74LVC1G07) to avoid bus contention, as done on the AM263x Control Card 3.

Follow up: Are you calling SOC_configureWarmResetSource() early in your application initialization, and would you like guidance on verifying the reset cause via SOC_getWarmResetCause() after the MCU restarts?

AM263Px Technical Reference Manual - Reset Chapter
MCU+ SDK API Guide - RCM Module
AM263Px Hardware Design Guide
AM263Px Datasheet - Pin Attributes

Once enabled, the input signal must remain LOW for at least TOP_RCM.WARM_RSTTIME3 duration to register an assertion, and HIGH for at least TOP_RCM.WARM_RSTTIME2 to register deassertion. These are configurable via SDK functions:

• SOC_configureWarmResetInputFallDelay() — sets WARM_RSTTIME3
• SOC_configureWarmResetInputRiseDelay() — sets WARM_RSTTIME2

Programmable values range from 500ns to 16.384ms 2.

1. AM263Px Technical Reference Manual - Reset Chapter
2. MCU+ SDK API Guide - RCM Module
3. AM263Px Hardware Design Guide
4. AM263Px Datasheet - Pin Attributes