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Richard Earnshaw writes: > > > scott@CS.Princeton.EDU said: > > There are no link errors. However, I know that my UART code is not in > > the executable. When I run the code, I get a "software interrupt". My > > guess is that the library is making some incorrect assumptions about > > the underlying environment. (This software interrupt sounds > > suspiciously like a system call.) > > > How can I use my simple little polling UART routines for stdio? > > > Newlib's libc is written using the "user+OS" mode, where accessing IO > devices is considered a privileged operation that has to be performed by > the operating system. The normal method for communicating with the > operating system in these circumstances is to call a software interrupt > (SWI) that asks the OS to perform the required action. To make newlib > tickle your UART routines you will either have to map the underlying SWI > handler to call your code, or you will have to rewrite the OS bits of > newlib to call your routines directly. Take a look in new/libc/sys/arm > for details. Thank you again for another helpful response. The board I am using has a loader pulls a coff image into memory and runs it. The code I will write will completely take control of the processor. To make a clean interface with newlib, it sounds like I should write my own SWI handler. This way I won't need to make changes to newlib. The files in newlib/libc/sys/arm seem to implement the "user" side of the interface. Before I write my own, is there source available which implements the "OS" side? Is there a published interface document for this? Thanks, Scott ------ Want more information? See the CrossGCC FAQ, http://www.objsw.com/CrossGCC/ Want to unsubscribe? Send a note to crossgcc-unsubscribe@sourceware.cygnus.com
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