Re: [Sdcc-user] Using idata for the stack on C8051

[Philipp K. K. <pk...@sp...>]

Am 08.02.2018 um 14:05 schrieb Maarten Brock:
>> According to the datasheet, the C8051F120 has 256 B __idata memory that
>> can be used for the stack. By default, SDCC uses the the 128B __data
>> memory (the lower part half of __idata) for the stack. And indeed, when
>> compiling a program using --model-large --stack-auto, it only uses
>> __data and runs out of stack space soon.
>> SDCC has the --xstack option to place the stack in the 256 B __pdata.
>>
>> But is using the 256 B __idata for the stack possible in SDCC?
>>
>> Philipp
> 
> SDCC already uses the full 256 bytes of __idata (minus registers, bits,
> and allocated variables and spills in __data/__idata). I don't understand
> why you believe it doesn't.
> 
> Using --xstack is less efficient than without. But it places return
> addresses on normal stack and data on xstack. Further xstack can use the
> full 256 bytes of __pdata. So it provides more stack space.
> 
> Maarten

I had a recursive test program that seemed to crash after using about
what I thought was about 128 B of stack space. But apparently that
program used even more stack space (I hadn't accounted for the stack
usage from a printf() call and there is probably more to be found).
Sorry for the noise.

Philipp