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76 lines
2.5 KiB
Markdown
76 lines
2.5 KiB
Markdown
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| Supported Targets | ESP32-S2 | ESP32-S3 |
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| ----------------- | -------- | -------- |
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# ULP-RISC-V bitbanged UART transmit:
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This example demonstrates how to program the ULP-RISC-V coprocessor to bitbang an UART TX line. This can be used to log output directly from the ULP, even when the main CPU is in deep sleep.
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## How to use example
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### Hardware Required
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The example can be run on any ESP32-S2 or ESP32-S3 based development board connected to a computer with a single USB cable for flashing and monitoring. The external interface should have 3.3V outputs. You may use e.g. 3.3V compatible USB-to-Serial dongle.
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### Setup the Hardware
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Connect the external serial interface to the board as follows.
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```
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-----------------------------------------------------------------------------------------
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| Target chip Interface | Kconfig Option | Default ESP Pin | External UART Pin |
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| ----------------------|--------------------|----------------------|--------------------
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| Transmit Data (TxD) | EXAMPLE_UART_TXD | GPIO4 | RxD |
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| Ground | n/a | GND | GND |
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-----------------------------------------------------------------------------------------
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```
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Note: Some GPIOs can not be used with certain chips because they are reserved for internal use. Please refer to UART documentation for selected target.
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### Configure the project
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Use the command below to configure project using Kconfig menu as showed in the table above. The baudrate can be changed with by configuring `ULP_RISCV_UART_BAUDRATE` under `components` -> `ULP`, but it is recommended to keep the baudrate low, as driver will not be able to accurately output higher rates.
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```
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idf.py menuconfig
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```
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### Build and Flash
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Build the project and flash it to the board, then run monitor tool to view serial output:
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```
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idf.py -p PORT flash monitor
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```
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(To exit the serial monitor, type ``Ctrl-]``.)
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See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.
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## Example Output
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Output from main CPU:
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```
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Not a ULP wakeup, initializing it!
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Entering in deep sleep
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```
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Output from ULP-RISCV:
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``
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Hello World from ULP-RISCV!
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Cnt: 0x00000000
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Hello World from ULP-RISCV!
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Cnt: 0x00000001
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Hello World from ULP-RISCV!
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Cnt: 0x00000002
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Hello World from ULP-RISCV!
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Cnt: 0x00000003
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Hello World from ULP-RISCV!
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Cnt: 0x00000004
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``
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## Troubleshoot
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If the received output contains garbled characters then try to lower the baudrate (ULP_RISCV_UART_BAUDRATE) using `menuconfig`.
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