Why is the AVR GCC compiler using a full `CALL` even though I have set the `-mshort-calls` flag?
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I have set the -mshort-calls flag which is documented to replace the 4 byte long CALL instruction with the 2 byte long RCALL instruction when possible to save flash space and and cycles...
Unfortunately the compiler is still using full CALL instructions even for a call that is only 2 bytes away...
...
35f6: 0e 94 fd 1a call 0x35fa ; 0x35fa
35fa: f8 94 cli
...
What am I doing wrong?
avr gcc rcall
asked 3 hours ago
bigjoshbigjosh
7,2801736
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add a comment |
$begingroup$
I have set the -mshort-calls flag which is documented to replace the 4 byte long CALL instruction with the 2 byte long RCALL instruction when possible to save flash space and and cycles...
Unfortunately the compiler is still using full CALL instructions even for a call that is only 2 bytes away...
...
35f6: 0e 94 fd 1a call 0x35fa ; 0x35fa
35fa: f8 94 cli
...
What am I doing wrong?
avr gcc rcall
asked 3 hours ago
bigjoshbigjosh
7,2801736
$endgroup$
add a comment |
$begingroup$
I have set the -mshort-calls flag which is documented to replace the 4 byte long CALL instruction with the 2 byte long RCALL instruction when possible to save flash space and and cycles...
Unfortunately the compiler is still using full CALL instructions even for a call that is only 2 bytes away...
...
35f6: 0e 94 fd 1a call 0x35fa ; 0x35fa
35fa: f8 94 cli
...
What am I doing wrong?
avr gcc rcall
asked 3 hours ago
bigjoshbigjosh
7,2801736
$endgroup$
I have set the -mshort-calls flag which is documented to replace the 4 byte long CALL instruction with the 2 byte long RCALL instruction when possible to save flash space and and cycles...
Unfortunately the compiler is still using full CALL instructions even for a call that is only 2 bytes away...
...
35f6: 0e 94 fd 1a call 0x35fa ; 0x35fa
35fa: f8 94 cli
...
What am I doing wrong?
avr gcc rcall
avr gcc rcall
asked 3 hours ago
bigjoshbigjosh
7,2801736
asked 3 hours ago
bigjoshbigjosh
7,2801736
edited 3 hours ago
bigjosh
asked 3 hours ago
bigjoshbigjosh
7,2801736
asked 3 hours ago
bigjoshbigjosh
7,2801736
asked 3 hours ago
bigjoshbigjosh
7,2801736
7,2801736
add a comment |
add a comment |
1 Answer
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It appears that this option changed at some point and not all the documentation was updated. Atmel Studio also still uses the obsolete flag.
The new option is called -mrelax on the compiler command line or --relax on the linker command line...
https://gcc.gnu.org/onlinedocs/gcc-4.9.2/gcc/AVR-Options.html
After adding that flag, the above code compiled to...
...
3584: 00 d0 rcall .+0 ; 0x3586
3586: f8 94 cli
...
If you happened to be using Atmel Studio, I put the flag here...
In my case, this change resulted in significant flash savings. If you are here because you also need to save flash space and/or cycles, I'd also recommend looking into enabling Link Time Optimization which also offers great savings at no cost.
answered 3 hours ago
bigjoshbigjosh
7,2801736
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1 Answer
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oldest
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1 Answer
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active
oldest
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votes
$begingroup$
It appears that this option changed at some point and not all the documentation was updated. Atmel Studio also still uses the obsolete flag.
The new option is called -mrelax on the compiler command line or --relax on the linker command line...
https://gcc.gnu.org/onlinedocs/gcc-4.9.2/gcc/AVR-Options.html
After adding that flag, the above code compiled to...
...
3584: 00 d0 rcall .+0 ; 0x3586
3586: f8 94 cli
...
If you happened to be using Atmel Studio, I put the flag here...
In my case, this change resulted in significant flash savings. If you are here because you also need to save flash space and/or cycles, I'd also recommend looking into enabling Link Time Optimization which also offers great savings at no cost.
answered 3 hours ago
bigjoshbigjosh
7,2801736
$endgroup$
add a comment |
$begingroup$
It appears that this option changed at some point and not all the documentation was updated. Atmel Studio also still uses the obsolete flag.
The new option is called -mrelax on the compiler command line or --relax on the linker command line...
https://gcc.gnu.org/onlinedocs/gcc-4.9.2/gcc/AVR-Options.html
After adding that flag, the above code compiled to...
...
3584: 00 d0 rcall .+0 ; 0x3586
3586: f8 94 cli
...
If you happened to be using Atmel Studio, I put the flag here...
In my case, this change resulted in significant flash savings. If you are here because you also need to save flash space and/or cycles, I'd also recommend looking into enabling Link Time Optimization which also offers great savings at no cost.
answered 3 hours ago
bigjoshbigjosh
7,2801736
$endgroup$
add a comment |
$begingroup$
It appears that this option changed at some point and not all the documentation was updated. Atmel Studio also still uses the obsolete flag.
The new option is called -mrelax on the compiler command line or --relax on the linker command line...
https://gcc.gnu.org/onlinedocs/gcc-4.9.2/gcc/AVR-Options.html
After adding that flag, the above code compiled to...
...
3584: 00 d0 rcall .+0 ; 0x3586
3586: f8 94 cli
...
If you happened to be using Atmel Studio, I put the flag here...
In my case, this change resulted in significant flash savings. If you are here because you also need to save flash space and/or cycles, I'd also recommend looking into enabling Link Time Optimization which also offers great savings at no cost.
answered 3 hours ago
bigjoshbigjosh
7,2801736
$endgroup$
It appears that this option changed at some point and not all the documentation was updated. Atmel Studio also still uses the obsolete flag.
The new option is called -mrelax on the compiler command line or --relax on the linker command line...
https://gcc.gnu.org/onlinedocs/gcc-4.9.2/gcc/AVR-Options.html
After adding that flag, the above code compiled to...
...
3584: 00 d0 rcall .+0 ; 0x3586
3586: f8 94 cli
...
If you happened to be using Atmel Studio, I put the flag here...
In my case, this change resulted in significant flash savings. If you are here because you also need to save flash space and/or cycles, I'd also recommend looking into enabling Link Time Optimization which also offers great savings at no cost.
answered 3 hours ago
bigjoshbigjosh
7,2801736
edited 3 hours ago
answered 3 hours ago
bigjoshbigjosh
7,2801736
answered 3 hours ago
bigjoshbigjosh
7,2801736
answered 3 hours ago
bigjoshbigjosh
7,2801736
7,2801736
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