MTDO Strapping for UART 0

[BarryAndrews]

Hello

We are using the ESP32-DOWDQ6 chip.
According to the ESP32 manual strapping the MTDP pin (GPIO15, pin 21) low, will stop the boot messages being sent to UART 0.

2.4 Strapping Pins
ESP32 has five strapping pins:
• MTDI
• GPIO0
• GPIO2
• MTDO
• GPIO5
Software can read the values of these five bits from register ”GPIO_STRAPPING”.
During the chip’s system reset (power-on-reset, RTC watchdog reset and brownout reset), the latches of the
strapping pins sample the voltage level as strapping bits of ”0” or ”1”, and hold these bits until the chip is powered
down or shut down. The strapping bits configure the device’s boot mode, the operating voltage of VDD_SDIO and
other initial system settings.
Each strapping pin is connected to its internal pull-up/pull-down during the chip reset. Consequently, if a strapping
pin is unconnected or the connected external circuit is high-impedance, the internal weak pull-up/pull-down will
determine the default input level of the strapping pins.
To change the strapping bit values, users can apply the external pull-down/pull-up resistances, or use the host
MCU’s GPIOs to control the voltage level of these pins when powering on ESP32.
After reset, the strapping pins work as normal-function pins.
Refer to Table 3 for a detailed boot-mode configuration by strapping pins.


I have tried this and it still outputs the messages, the only way I can stop messages is to use make menuconfig to set bootloader output to None.

A couple of annoying things here when you are trying to debug what is happening.

First:
It states "users can apply the external pull-down/pull-up resistances", how about specifying the values to use for these external pull up / pull down or provide an example circuit if you need an open collector or such. I have searched high and low and no document or forum post mentions what value resistor, or indeed what circuit is needed to successfully strap MTDO to achieve a 0.

Second:
All through the manual ESP32 continuously refers to week pull up or weak pull down but no where does it specify the range of these resistors so you can work out what you need to use to externally strap. Surely its not too hard to add to the ESP32 manual the values for these resistors.

Can someone please point me to a circuit that shows how MTDO should be strapped, or is it best that I just disable the boot messages in the make menuconfig and not worry about MTDO.




1

[WiFive]

There are 2 bootloaders, strapping pin controls 1st, menuconfig controls 2nd. Internal pull is 30-40k I believe.