Hello Maarten, Ahaa..., many thanks for this explanation of 'spilled location'. As I still often use assembler on the 51 I know that working with external memory is an expensive task to do for the processor. If it would just be a question of speed then there would be no problem (silabs running at 100Mhz today) but I know that the problem mainly consist of moving data from one location to another. Just one final question: would you then agree to the somewhat generic statement that sdcc would do much better in allocating memory if it is told how to do so, i.e. if I put some variables deliberately into DATA instead of telling sdcc by the model large to allocate everything in XDATA?
thanks again, Felix ------------------------- Felix Maarten Brock wrote: > Felix, > It's a bit more complicated than what's written in the > manual but the basics are correct. When using large > memory model and no reentrancy all automatics are placed > in xdata by default. But xdata is expensive to use, > because everything must be done through the accumulator > and data pointer. Consider a simple addition: > x = y + z; > SDCC must get y from xdata into ACC and temporarily > store it somewhere because it needs ACC again to get z > from xdata. SDCC tries to store it in a register, but > when it needs to remember a lot of those, the registers > are used up and it reverts to using spill locations in > DATA. When it has taken z into ACC it can add y to it > and finally store ACC to x. > Now what if y which was spilled to data never really > gets used without the spill location? Then there no > longer is any reason to allocate memory for it in XDATA! > So SDCC ends up renaming the spill location sloc to the > real name y. > When using large memory model SDCC might need alot of > those spill locations and they can fill up all data > memory without having one single variable put there by > the user. The fact that SDCC is not good at overlaying > only makes this worse. > Maarten ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Sdcc-user mailing list Sdcc-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/sdcc-user
