Re: [hatari-devel] Dynamic Bus Sizing and I/O Register Access

[Andreas Grabher <andreas_g86@xxxxxxxxxx>]

> Am 12.01.2024 um 20:14 schrieb Thomas Huth <th.huth@xxxxxxxxx>:
> 
> Am Fri, 12 Jan 2024 19:58:00 +0100
> schrieb Andreas Grabher <andreas_g86@xxxxxxxxxx>:
> 
>>> Am 12.01.2024 um 19:41 schrieb Thomas Huth <th.huth@xxxxxxxxx>:
>>> 
>>> Yes, right. This basically depends on what your I/O hardware (like the
>>> "glue" on the ST) is doing with the accesses on the bus.
>>> 
>>> Do you know what's supposed to happen if the bootloader write a 32-bit word
>>> to 0x02010000 ? For example, if it wrote 0x12345678 to that address, which
>>> byte is supposed to end up in the brightness register?
>>> 
>>> Thomas  
>> 
>> In this example on real hardware (68030) it would write 0x78.
> 
> Ok, that's quite different compared to the I/O registers on the Atari (but
> perfectly possible if the NeXT hardware has been designed that way). I think
> in that case you have to read the value from 
> 
> IoMem[(IoAccessCurrentAddress + nIoMemAccessSize - 1) & IO_SEG_MASK]
> 
> instead.
> 
> HTH,
>  Thomas
> 

I’not sure this is specific to NeXT. There is a chapter about dynamic bus sizing in the user manual of the 68030 and this does not seem to be implemented in Hatari.

Regards,
Andreas