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Thread
2005-11-21 by Gus
put the following code in a file and compile it. it takes 240 byte
of RAM!!!!!!
Can anyone explain why?
Remove any one of the cases and the RAM usage goes down to NONE!!!
int foo(int i)
{
switch (i)
{
case 0x22:
case 0x2A:
case 0x2B:
case 0x3E:
case 0x5C:
case 0x5D:
return 12;
break;
}
}2005-11-21 by Tom Walsh
Gus wrote:
>put the following code in a file and compile it. it takes 240 byte
>of RAM!!!!!!
>
>Can anyone explain why?
>Remove any one of the cases and the RAM usage goes down to NONE!!!
>
>int foo(int i)
>{
> switch (i)
> {
> case 0x22:
> case 0x2A:
> case 0x2B:
> case 0x3E:
> case 0x5C:
> case 0x5D:
> return 12;
> break;
> }
>}
>
>
>
Perhaps you can explain it to yourself, did you try taking a look at
the listing file (lss) or did you try an arm-elf-objdump -S -D
<filename.obj) to see what is "in there" ??
TomW
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--
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------------------------------------------2005-11-21 by Paul Curtis
Gus, I don't see this take any static RAM. Why do you think it does? -- Paul Curtis, Rowley Associates Ltd http://www.rowley.co.uk CrossWorks for MSP430, ARM, AVR and now MAXQ processors
> -----Original Message-----
> From: Gus [mailto:gus_is_working@...]
> Sent: 21 November 2005 01:45
> To: lpc2000@yahoogroups.com
> Subject: [lpc2000] unexplained RAM use on GCC and CrrosWorks
>
> put the following code in a file and compile it. it takes 240 byte
> of RAM!!!!!!
>
> Can anyone explain why?
> Remove any one of the cases and the RAM usage goes down to NONE!!!
>
> int foo(int i)
> {
> switch (i)
> {
> case 0x22:
> case 0x2A:
> case 0x2B:
> case 0x3E:
> case 0x5C:
> case 0x5D:
> return 12;
> break;
> }
> }
>
>
>
>
>
>
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> Yahoo! Groups Links
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>2005-11-21 by Paul Curtis
Gus, > When I look at the memory usage in CrossStudio, I see 240 bytes and > then when I remove any one of the "cases" the usage goes down to 0! *Where* do you see this and get this number from? If it's "data" then data encompasses data placed into flash, IIRC. > Even if this goes on the stack. 0 to 240 is a big change for just > one more "case" Depends upon how the case statement is codegen'd. If it's a table-based approach, I would expect a table in flash with a number of entries. If it's if-then-else'd then it will bot have a table in flash. Adding a single case element is enough to switch between the two, I would guess. -- Paul Curtis, Rowley Associates Ltd http://www.rowley.co.uk CrossWorks for MSP430, ARM, AVR and now MAXQ processors
2005-11-21 by Gus
When I look at the memory usage in CrossStudio, I see 240 bytes and then when I remove any one of the "cases" the usage goes down to 0! Even if this goes on the stack. 0 to 240 is a big change for just one more "case" Gus --- In lpc2000@yahoogroups.com, "Paul Curtis" <plc@r...> wrote: > > Gus, > > I don't see this take any static RAM. Why do you think it does? > > -- > Paul Curtis, Rowley Associates Ltd http://www.rowley.co.uk > CrossWorks for MSP430, ARM, AVR and now MAXQ processors > > > -----Original Message----- > > From: Gus [mailto:gus_is_working@y...] > > Sent: 21 November 2005 01:45 > > To: lpc2000@yahoogroups.com > > Subject: [lpc2000] unexplained RAM use on GCC and CrrosWorks > > > > put the following code in a file and compile it. it takes 240 byte > > of RAM!!!!!! > > > > Can anyone explain why? > > Remove any one of the cases and the RAM usage goes down to NONE!!!
> >
> > int foo(int i)
> > {
> > switch (i)
> > {
> > case 0x22:
> > case 0x2A:
> > case 0x2B:
> > case 0x3E:
> > case 0x5C:
> > case 0x5D:
> > return 12;
> > break;
> > }
> > }
> >
> >
> >
> >
> >
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>2005-11-21 by Gus
I think you are right! It generats a 240 byte jump table! Still seem to be overkill Gus --- In lpc2000@yahoogroups.com, "Paul Curtis" <plc@r...> wrote: > > Gus, > > > When I look at the memory usage in CrossStudio, I see 240 bytes and > > then when I remove any one of the "cases" the usage goes down to 0! > > *Where* do you see this and get this number from? If it's "data" then > data encompasses data placed into flash, IIRC. > > > Even if this goes on the stack. 0 to 240 is a big change for just > > one more "case" > > Depends upon how the case statement is codegen'd. If it's a table- based > approach, I would expect a table in flash with a number of entries. If > it's if-then-else'd then it will bot have a table in flash. Adding a > single case element is enough to switch between the two, I would guess.
> > -- > Paul Curtis, Rowley Associates Ltd http://www.rowley.co.uk > CrossWorks for MSP430, ARM, AVR and now MAXQ processors >
2005-11-21 by John Heenan
I am impressed GCC for ARM looks to use genuine jump tables. This is how the code worked in an assembly listing. A branch to a jump table was made if the value passed in was between the minimum and maximum case values. This took only three instructions: sub... ;subtract minimum from value passed in cmp... ;compare result with maximum-minimun constant value ldrls pc,... ;if result is less than maximum-minimum then use result as as an index value into a table to determine where to branch to next The size of the jump table is the difference between the maximum and minimum case values + 1. The jump table contained one of two values: a location to branch to corresponding to the action to take if any of the case values was satisfied or a location to branch to if there was no case match between the minumum and maximum case values. John Heenan --- In lpc2000@yahoogroups.com, "Gus" <gus_is_working@y...> wrote:
> > I think you are right! It generats a 240 byte jump table! Still seem > to be overkill > > Gus