Oh, seems like it is from the 16-bit pointer limitation http://lists.nongnu.org/archive/html/avr-gcc-list/2008-07/msg00050.html
avr-libc's puts_P uses pgm_read_byte(), which gives no warning and is not documented in the stdio portion of the manual. Maybe we can use pgm_read_byte_far()? That would make the functions work on a larger range of devices, with a small(?) performance penalty. On Tue, Aug 16, 2016 at 2:56 PM, Tavish Naruka <tavishnar...@gmail.com> wrote: > Hi > > I'm linking a program as a bootloader with --section-start, everything is > working fine, except that stdio functions with _P do not work as expected, > once I link the same program with --section-start=0x00, it works just fine. > I am not sure but it seems to me that only 16-bit addresses are working > since only registers r24 and r25 are being used for the function calls. > Here is the difference in the generated assembly: > > Function call is puts_P(NOT_PRESSED_STR). > > Linked at 0x00-: > > 000000e4 <NOT_PRESSED_STR>: > e4: 4e 6f 74 20 50 72 65 73 73 65 64 0a 00 Not Pressed.. > > > 1d6: 00 00 nop > 1d8: 84 ee ldi r24, 0xE4 ; 228 > 1da: 90 e0 ldi r25, 0x00 ; 0 > 1dc: 0e 94 f2 00 call 0x1e4 ; 0x1e4 <puts_P> > > > Linked at 0x1E000-: > > 0001e0e4 <NOT_PRESSED_STR>: > 1e0e4: 4e 6f 74 20 50 72 65 73 73 65 64 0a 00 Not > Pressed.. > > 1e1d6: 00 00 nop > 1e1d8: 84 ee ldi r24, 0xE4 ; 228 > 1e1da: 90 ee ldi r25, 0xE0 ; 224 > 1e1dc: 0e 94 f2 f0 call 0x1e1e4 ; 0x1e1e4 <puts_P> > > I haven't been able to find a workaround yet, so I'll use strings in > initialized data section for now. > > -- > Regards > Tavish Naruka > -- Regards Tavish Naruka
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