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Discussion Groups | Analog Devices DSPs | ADSP 2191-Alu overflow latch mode
Technical discussions related to Analog Devices DSPs (including Blackfin, TigerSHARC, SHARC and ADSP-21xx DSPs).
ADSP 2191-Alu overflow latch mode - tio tio - Nov 2 9:30:00 2003
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Dear members, I am newbie and this mode is blurred for me. I know that one of the ways to process overflows is the saturation and adsp 2191 supports this mode, but I read from adsp219x/2192 dsp hardware reference that these processors support ALU overflow latch mode yet. This issue is not clear explained in the book and I would like someone to point me references which explain this mode or explains me briefly. Thanks in advance, Tio
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Re: ADSP 2191-Alu overflow latch mode - Mike Rosing - Nov 3 3:09:00 2003
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On Sun, 2 Nov 2003, tio tio wrote: > Dear members, > I am newbie and this mode is blurred for me. I know that one of the ways to process overflows is the saturation and adsp 2191 supports this mode, but I read from adsp219x/2192 dsp hardware reference that these processors support ALU overflow latch mode yet. This issue is not clear explained in the book and I would like someone to point me references which explain this mode or explains me briefly. The basic idea is that overflow "sticks" on. So when you get a value that would normally wrap around in two's complement form, it instead saturates and stays at the most positive or most negative value (depending on overflow direction). You can check the overflow bits to see if it happened at the end of a block of arithmetic rather than every operation. I don't know if the 2192 has a "sticky bit", but check the alu status registers for them. The advantage in signal processing is that you can still output the value, you just get clipping rather than noise. It gives you a chance to change the gain without the human noticing too much. Patience, persistence, truth, Dr. mike |
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Re: ADSP 2191-Alu overflow latch mode - tio tio - Nov 4 15:38:00 2003
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Hello Dr. Mike
and thanks for your response. I understood that AV_Latch defines if the state of flag AV to stick
(to remain constantly, and we can change it by direct writting from DMD bus). But it is not very cleared for me what is the advantage of this mode. Can you give me some examples show the advantage of latch mode. Best Regards,
Tio Mike Rosing <e...@eskimo.com> wrote: On Sun, 2 Nov 2003, tio tio wrote:
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Re: ADSP 2191-Alu overflow latch mode - Mike Rosing - Nov 4 17:57:00 2003
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On Tue, 4 Nov 2003, tio tio wrote: > I understood that AV_Latch defines if the state of flag AV to stick > (to remain constantly, and we can change it by direct writting from > DMD bus). But it is not very cleared for me what is the advantage of > this mode. Can you give me some examples show the advantage of latch > mode. The advantage is that you can go faster. Suppose you have 5 additions in a series. You can check for overflow on every addition, and then you take 10 cycles. Or you can check the "sticky" bit after 5 additons to see if an error occured. That's only 6 cycles. You have saved 40% of your MIPS for something else, and still know there's a problem. And you have time to fix it too! Patience, persistence, truth, Dr. mike |
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