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42 lines
2.0 KiB
Markdown
42 lines
2.0 KiB
Markdown
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---
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title: Debugging steps for CDC USB on STM32 and Platformio
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author: peter
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date: 2024-03-02 21:58:54 +0800
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categories: [Electronics] # Blogging | Electronics | Programming | Mechanical
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tags: [electronics, STM32, platformio] # systems | embedded | rf | microwave | electronics | solidworks | automation
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# image: assets/img/2024-03-02-Debugging-steps-for-/preview.png
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---
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Progress to the next step if it still isn't working
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## Step 1: Have you put the required defines in your build flags?
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The build flags enable the USB CDC functionality. Make sure to also set the CPU frequency, on my board I've used a 16 MHz crystal.
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```ini
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[env:genericSTM32F103C8]
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platform = ststm32
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board = genericSTM32F103C8
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framework = arduino
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upload_protocol = stlink
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debug_tool = stlink
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board_build.f_cpu = 16000000L ; This should match your crystal oscillator frequency (On my board I've used a 16 MHz crystal)
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monitor_dtr = 1
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build_flags =
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-D PIO_FRAMEWORK_ARDUINO_ENABLE_CDC
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-D USBCON
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```
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## Step 2: Does your MCU require a 1.5kR pullup resistor?
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Consult ST application note [AN4879](https://www.st.com/resource/en/application_note/dm00296349-usb-hardware-and-pcb-guidelines-using-stm32-mcus-stmicroelectronics.pdf), Table 3. Find your MCU series and check the "Embedded pull-up resistor on USB_DP line" column. In my case, unfortunately, I forgot to put the 1.5kR pullup resistor and I am using an STM32F103, which has a `-` in that column. The note (2) states:
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> To be compliant with the USB 2.0 full-speed electrical specification, the USB_DP (D+) pin must be pulled up to a voltage in the 3.0 to 3.6 V range with a 1.5 kΩ resistor.
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Try putting a resistor on `USB_DP`, then reset and re-connect the MCU to your host device. It should work with any low-value resistor, in my case I used a 10kR through hole resistor since I was not at my lab. This worked and I received characters as long as the resistor was held there.
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## Step 3: ???
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I've solved my issue with my custom board, but if you took more debugging steps feel free to leave your solutions in the comments below and I'll add them here.
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