Re: [Gumstix-users] weird PWM behaviour using Robostix timer/counter 1 vs. 3

[Dave H. <dhy...@gm...>]

Hi Mathias,

> This depends on the compiler/header files you use.  For example,
> gcc for avr has defines for all these I/O-registers.  The include files
> distinguish between registers that in I/O- and memory-space, and the
> compiler will then generate the correct code to access them.
>
> Snippets from /usr/avr/include/avr/iom128.h (ATmega128):
>
>         /* Timer/Counter 1 Control and Status Register */
>         #define TCCR1B    _SFR_IO8(0x2E)
>
> is in I/O space and can be access with IN and OUT instructions, whereas
>
>
>         /* Timer/Counter 3 Control Register B */
>         #define TCCR3B    _SFR_MEM8(0x8A)
>
> is in memory space and must be accessed with direct addressing
> (LDS/STS) or X, Y, or Z register indirect.
>
> At least in gcc, you don't need to have functions to read/write to/from
> I/O registers or ports, but can use them like any scalar variable.
>
> What development system/compiler/library are you using, Paul?

I'll interject here.

Paul's code runs on the gumstix, and not on the AVR, so including the
AVR header files isn't an option.

I had created i2c-io which also runs on the gumstix and it allows the
registers to be referred to symbolically. I'm assuming that Paul
copied the defines from that source file, but I could be wrong.

It talks to the portion of i2c-io that runs on the robostix, and it
just gets a register address and a value and it stores the value at
the address so it always uses the memory mapped address and not the
I/O address.

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/