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A general SWD interface based upon K20

Question asked by Kai Liu on Dec 27, 2013
Latest reply on Jan 18, 2014 by Kai Liu

PS: If anyone thinks this discussion is against interests of FSL, please let me know, I will remove the thread, anyway.


FRDM offers a unique approach to reuse its USB interface with different appliation firmware as programmer, debugger and UART bridge. Although FRDM's K20 is close source, it is not very difficult to reuse the off-the-shelf firmware to make FRDM as a general SWD interface based upon K20D50.


After reading blogs from, I found it is possible to design a standalone SWD interface based upon K20 micro. The hardware design comes from FRDM boards, the application firmware is ready. We just need a USB MSD bootloader, which has been offered by Freescale. I have checked the firmware, most of them starts from 32KB, which means the first 32KB is reserved for bootloader.


I know PEmicro, JLINK lite are protected to support same micro with target one. But CMSIS-DAP is almost designed for open source.


I have not evalueted all the firmware packages from PEmicro, Keil, mBed, Freescale, OSBDM, OSjtag. However I have successfully programmed off-chip microcontrollers (including FSL and non-FSL micro) with CMSIS-DAP firmware in Keil.


But I do find error reports why I try to debug micro with CMSIS-DAP firmware.


I would like to ask questions to whom have FRDM-K20D50M at hand.

Has anyone ever tried to download these firmware to use K20D50M as a SWD programmer? Since OpenSDA K20 and target K20 are using different package. I would like to use QFP48 packge, instead of QFN and QFP80 to support easy soldering.


I would like to open the design and when I finish evaluting all these questions.




Currently I am trying to evalue all kinds of bootloaders for this projects, since there is no off-the-shelf solution from FSL. McHack's DFU bootloader may work, and I am going to port AN4379 to K20 as well.



Allan K Liu