{"id":365095,"date":"2024-05-21T02:30:50","date_gmt":"2024-05-21T02:30:50","guid":{"rendered":"http:\/\/savepearlharbor.com\/?p=365095"},"modified":"-0001-11-30T00:00:00","modified_gmt":"-0001-11-29T21:00:00","slug":"","status":"publish","type":"post","link":"https:\/\/savepearlharbor.com\/?p=365095","title":{"rendered":"STM32 without any trouble<\/span>"},"content":{"rendered":"
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Easy Marlin installation on STM32 debug board<\/p>\n

Confusion over bootloaders<\/strong><\/p>\n

Here\u2019s a brief historical and technical overview to help us understand what a bootloader is, why you need it, and what it has to do with Marlin and STM32.<\/p>\n

Arduino<\/strong><\/p>\n

Arduino boards use a special bootloader that allows you to update the microcontroller firmware without a programmer. This bootloader is not part of the microcontroller, but is pre-flashed into it by the board manufacturer and is never changed.<\/p>\n

In 2009, leaflabs tried to produce its own line of Arduino-like boards based on STM32. A set of libmaple libraries and a special loader were developed for Arduino compatibility. This initiative did not have any notable success, and in 2015 the libmaple project was closed.<\/p>\n

Marlin has never used or supported the bootloader from leaflabs.<\/p>\n

STM32<\/strong><\/p>\n

STM32 microcontrollers have a built-in bootloader, which allows you to upload firmware without using a programmer or debugger. The bootloader is stored in the microcontroller\u2019s non-volatile ROM and cannot be corrupted or deleted without physically damaging the chip.<\/p>\n

A special BOOT0 pin is used to activate this bootloader. Depending on the signal applied to it at power-up or reboot, control is transferred either to custom firmware (low signal level) or to the built-in bootloader (high signal level).<\/p>\n

The built-in bootloader allows one to upload the firmware using UART or USB connection. The latter option is available only on STM32F4 and newer microcontrollers.<\/p>\n

Marlin<\/strong><\/p>\n

In December 2018, Marlin introduced support for the MKS Robin board with its proprietary bootloader, which allowed firmware updates from an encrypted file on the SD card. The MKS bootloader is stored at the beginning of the flash memory and from the microcontroller\u2019s point of view is custom firmware. The firmware for MKS Robin had to be built using a non-standard location on the flash memory.<\/p>\n

The ability to update the firmware from an SD card proved to be a decisive factor, and in spring 2019, BTT SKR Mini v1.1\u2014the first commercial STM32-based 3D printer control board made specifically for Marlin 2.0\u2014appeared on the market. Naturally, it had its own loader, but the general working principle did not change.<\/p>\n

All STM32-based 3D printer control boards on the market use the manufacturer\u2019s bootloader that allows you to update the firmware from an SD card. The size of such a loader depends on its functionality as well as the developer and varies from 8 to 64 kb. When you see mentions of a damaged bootloader, it\u2019s all about this one.<\/p>\n

In case of debug boards manufacturers don\u2019t bother with a bootloader because it\u2019s completely unnecessary. Flashing through the ST-Link debugger is infinitely easier, and if the developer needs a non-standard bootloader, he can flash it himself, and with exactly the right functionality.<\/p>\n

If, for some reason, ST-Link is not available, there is always the possibility of flashing the debug board via the built-in bootloader.<\/p>\n

Thus, when the word «bootloader» is used in relation to STM32, its meaning depends on the context. On a 3D printer control board, it\u2019s a manufacturer\u2019s bootloader, stored at the beginning of the flash memory, which allows updating the firmware from the SD card. On the debug board, it\u2019s a built-in bootloader that uses its own ROM without taking up any space in flash memory.<\/p>\n

Choosing a debug board<\/strong><\/p>\n

Any debug board can be used, but it\u2019s worth considering that the availability of documentation saves you from having to manually create a pinout diagram, which is a huge time-saver.<\/p>\n

Debug boards from STMicroelectronics Nucleo and Discovery series are well documented and come with a built-in ST-Link debugger. However, they cost more than their Chinese alternatives.<\/p>\n

As a starting point for board selection, you can use the STM32-base project, which describes many popular debug boards on various STM32 microcontrollers.<\/p>\n

I have two boards from this list lying around, so I will use them:<\/p>\n