How to enable SWD debugging on PyBoard V1.1 #16782

projectgus · 2025-02-18T23:23:37Z

projectgus
Feb 18, 2025
Collaborator

(This is partially a note-to-self for future me, but I've seen other people struggle with this as well.)

It's possible to use SWD to low-level debug the C firmware of a PyBoard V1.1 (PYBV11) and probably V1.0 as well, but it requires some fiddling.

Connections

The SWD pins are P4 (SWCLK) and P5 (SWDIO) as shown on the PyBoard Schematic. Plugged in it looks like this:

The SWCLK pin is the white pin header above X20, and the SWDIO pin is the white pin header above X21.

In this photo the RST pin is not connected from the SWD debugger, but it's recommended to connect this as well.

Custom MicroPython Build

Unfortunately P4 (GPIO PA14) and P5 (GPIO PA15) are also LED1 and LED2. These are set by the mboot bootloader on each boot to indicate the boot status. This re-muxes the SWD pins and effectively disables SWD.

It's possible to apply a temporary patch like this to re-assign LED1 and LED2, then build and flash a custom firmware:

diff --git a/ports/stm32/boards/PYBV11/mpconfigboard.h b/ports/stm32/boards/PYBV11/mpconfigboard.h
index c8f660c8fb..b0f953b140 100644
--- a/ports/stm32/boards/PYBV11/mpconfigboard.h
+++ b/ports/stm32/boards/PYBV11/mpconfigboard.h
@@ -82,12 +82,12 @@
 #define MICROPY_HW_USRSW_PRESSED    (0)
 
 // The pyboard has 4 LEDs
-#define MICROPY_HW_LED1             (pin_A13) // red
-#define MICROPY_HW_LED2             (pin_A14) // green
-#define MICROPY_HW_LED3             (pin_A15) // yellow
-#define MICROPY_HW_LED4             (pin_B4)  // blue
-#define MICROPY_HW_LED3_PWM         { TIM2, 2, TIM_CHANNEL_1, GPIO_AF1_TIM2 }
-#define MICROPY_HW_LED4_PWM         { TIM3, 3, TIM_CHANNEL_1, GPIO_AF2_TIM3 }
+// #define MICROPY_HW_LED1             (pin_A13) // red
+// #define MICROPY_HW_LED2             (pin_A14) // green
+#define MICROPY_HW_LED1             (pin_A15) // yellow
+#define MICROPY_HW_LED2             (pin_B4)  // blue
+#define MICROPY_HW_LED1_PWM         { TIM2, 2, TIM_CHANNEL_1, GPIO_AF1_TIM2 }
+#define MICROPY_HW_LED2_PWM         { TIM3, 3, TIM_CHANNEL_1, GPIO_AF2_TIM3 }
 #define MICROPY_HW_LED_ON(pin)      (mp_hal_pin_high(pin))
 #define MICROPY_HW_LED_OFF(pin)     (mp_hal_pin_low(pin))

Note: I also find the "connect-under-reset" option is generally necessary for establishing an SWD connection with MicroPython stm32 port.

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How to enable SWD debugging on PyBoard V1.1 #16782

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MicroPython

How to enable SWD debugging on PyBoard V1.1 #16782

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projectgus Feb 18, 2025 Collaborator

Connections

Custom MicroPython Build

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projectgus
Feb 18, 2025
Collaborator