Re: [hatari-devel] view the DSP stack?

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

On 17/02/2013 21:22, Laurent Sallafranque wrote:
> Hi Doug,
>
> Thanks a lot. I've uploaded a patch, if you can verify it.
>
> I've also patched another instruction that I think was wrong timing :
>
> P:ext  JSR ext_addr
>
> Maybe you can test it too with my newpatch to verify if it's OK now ?
>
> Eero, The way I've done this patch is probably not the most optimized :
>
> I use one variable (access_to_ext_memory) as a 3 FLAG bits variable :
>   - 1st bit for access to X external memory
>   - 2nd bit for access to Y external memory
>   - 3rd bit for access to P external memory
>
> Then I have to slide the bits to count how many access I did to external
> memory.
>
>
> 	/* Add the waitstate due to external memory access */
>   +	/* (2 extra cycles per extra access to the external memory after the first one */
>   +	if (access_to_ext_memory != 0) {
>   +		value = access_to_ext_memory & 1;
>   +		value += (access_to_ext_memory & 2) >> 1;
>   +		value += (access_to_ext_memory & 4) >> 2;
>   +		
>   +		if (value > 1)
>   +			dsp_core.instr_cycle += (value - 1) * 2;
>   +	}
>   +
>
>
> If you think there's a more optimized way to do it, just don't hesitate
> to change it.

Hello

given there're only 3 bits, this makes 8 cases, so you can store the 
number of 1 bits in a small array and avoid any if/and/shift :

eg :

count_bit[8] = { 0,1,1,2,1,2,2,3 };

value = count_bit[ access_to_ext_memory ];
if (value > 1)
	dsp_core.instr_cycle += (value - 1) * 2;

Or you could even store (value-1)*2 in the array and do directly

dsp_core.instr_cycles += access_to_ext_memory_penalty[access_to_ext_memory]

6 lines packed into 1, with maximum speed ;)

Nicolas