文件列表:

example-payload-flash/
example-payload-ram/
LICENSE
Makefile
bootloader.c
linker.lds
startup.S

# WCH RISC-V UF2 Bootloader This code implements a [uf2](https://github.com/microsoft/uf2) bootloader for RISC-V microcontrollers from [WCH](https://www.wch-ic.com). This allows user-friendly uploading of code by dragging files onto a virtual USB Mass Storage device (i.e. a pretend thumb drive). This means that, unlike the vendor ISP bootloader, no special software is required. ## Usage notes - Triggered by a double reset within 0.5 seconds (like Adafruit bootloaders) - Needs usage of `R16_BKP_DATAR10` - Write 0x4170 ('Ap') to boot into the application immediately without delay - Write 0x624c ('bL') to unconditionally enter the bootloader - Fits in $\leq$ 4096 bytes - Tested and built with MounRiver GCC V1.91 - Code size is improved through use of "XW" instructions, which are not upstream - Supports USBD peripheral *only* (i.e. not USBFS) - USBD and USBFS are completely different, and the QFN28 package (which is available in largest quantities on LCSC) only bonds out USBD - Note that USBD requires a USB A-A cable if using the official devkit - Runs off of internal 8 MHz oscillator (despite stability concerns) - The HSI oscillator's tolerance (-1.0% to +1.6%) is well outside of the range specified for USB full speed ($\pm$ 0.25%), but it seems to work in practice n=1 \\\_(ツ)\_/ - The vendor's ISP ROM bootloader also does this - Should work across most of the CH32V2xx and CH32V3xx family with appropriate changes to hardcoded constants. - Allows both download to flash and to SRAM with the "not main flash" flag (this is how the RP2040 bootrom works) - Flash download address must be 08xxxxxx (i.e. not starting at 0) - SRAM download address must be 20xxxxxx - The entire size of the SRAM can be used, as USBD contains its own buffer memory independent of the main SRAM - Auto-reboot on complete download, _but_ **only** works if the download is sufficiently small. Larger downloads will of course still flash, but they will not trigger auto-reboot and a manual reboot will be required. - Lots of nasty code golfing tricks -- see comments in [bootloader.c](https://github.com/ArcaneNibble/wch-uf2/blob/main/bootloader.c) ## Examples There are two included examples which build "blinky" applications (that blink pin PA0). The "RAM" example blinks at a different speed than the "flash" example so that you can tell that you've successfully loaded it. The examples do *not* use a verbatim copy of the vendor startup bits -- some elements which we (IANAL) consider to be purely functional have been borrowed, but other things have been changed substantially: - Vector table isn't hardcoded in the startup assembly file (as it doesn't need to be located at the beginning of flash, this isn't necessary) - Preinit, init, and fini functions (`.init_array`, e.g. `__attribute__((constructor))` and (untested) C++ static constructors) are properly called - Legacy `.init` is *not* called - Various initialization for CSRs, interrupt handling, etc. are not hardcoded in the startup assembly code. The intention is that this can be done with `__attribute__((constructor))`. The example Makefiles contain a horrible hardcoded path to `uf2conv.py`. This needs to be fixed before they will work on your computer.

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