Re: How can I link the kernel with libgcc ?

Re: How can I link the kernel with libgcc ?

[Lee Revell]

(added alsa-devel to cc:)

On Thu, 2006-03-09 at 19:01 -0800, Carlos Munoz wrote:
> >Audio drivers should never have to directly manipulate the samples -
> >they just manage the DMA buffers and interrupts and wake up the process
> >at the right time.  Mixing, routing, volume control, DSP go in
> >userspace.
>
> Unfortunately, the driver needs to populate several coefficient tables 
> for the hardware to perform silence suppression and other advance 
> features. The values for these tables are calculated using log10 
> operations. I don't  see a clean way to push these operations to user 
> space without the need for custom applications that build the tables and 
> pass them to the driver.

Unless you can do it with fixed point math, or use a static table, you
might have to do just that, with a sysfs interface.  For example the
emu10k1 driver uses an ioctl interface to upload code to the built in
(floating point) DSP.  But new ioctls are frowned upon...

Lee



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Re: How can I link the kernel with libgcc ?

[Lee Revell]

On Thu, 2006-03-09 at 19:25 -0800, Carlos Munoz wrote:
> I figured out how to get the driver to use floating point operations.
> I included source code (from an open source math library) for the
> log10 function in the driver. Then I added the following lines to the
> file arch/sh/kernel/sh_ksyms.c: 

Where is the source code to your driver?

Lee

Re: How can I link the kernel with libgcc ?

[Carlos Munoz]

[-- Attachment #1: Type: text/plain, Size: 879 bytes --]

Lee Revell wrote:

>On Thu, 2006-03-09 at 19:25 -0800, Carlos Munoz wrote:
>  
>
>>I figured out how to get the driver to use floating point operations.
>>I included source code (from an open source math library) for the
>>log10 function in the driver. Then I added the following lines to the
>>file arch/sh/kernel/sh_ksyms.c: 
>>    
>>
>
>Where is the source code to your driver?
>
>Lee
>
>  
>
Hi Lee,

Be warned. This driver is in the early stages of development. There is 
still a lot of work that needs to be done (interrupt, dma, etc, etc).

You can untar it in the linux/sound directory (it will overwrite the 
Kconfig and Makefile) and it will build (you will need to modify the 
arch/....../kernel/ksyms.c to resolve the undefined symbols, see my 
previous email). It won't do anything useful yet. Please let me know if 
you have any questions.

Thanks,


Carlos Munoz

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Re: How can I link the kernel with libgcc ?

[Denis Vlasenko]

On Friday 10 March 2006 05:47, Carlos Munoz wrote:
> Lee Revell wrote:
> 
> >On Thu, 2006-03-09 at 19:25 -0800, Carlos Munoz wrote:
> >  
> >
> >>I figured out how to get the driver to use floating point operations.
> >>I included source code (from an open source math library) for the
> >>log10 function in the driver. Then I added the following lines to the
> >>file arch/sh/kernel/sh_ksyms.c: 
> >>    
> >>
> >
> >Where is the source code to your driver?
> >
> >Lee
> >
> >  
> >
> Hi Lee,
> 
> Be warned. This driver is in the early stages of development. There is 
> still a lot of work that needs to be done (interrupt, dma, etc, etc).

What? You are using log10 only twice!

        if (!(siu_obj_status & ST_OPEN)) {
		...
                /* = log2(over) */
                ydef[22] = (u_int32_t)(log10((double)(over & 0x0000003f)) /
                                       log10(2));
		...
        }
        else {
		...
                if (coef) {
                        ydef[16] = 0x03045000 | (over << 26) | (tap - 4);
                        ydef[17] = (tap * 2 + 1);
                        /* = log2(over) */
                        ydef[22] = (u_int32_t)
                                (log10((double)(over & 0x0000003f)) / log10(2));
                }

Don't you think that log10((double)(over & 0x0000003f)) / log10(2)
can have only 64 different values depending on the result of (over & 0x3f)?

Obtain them from precomputed uint32_t log10table[64].
--
vda

Re: How can I link the kernel with libgcc ?

[Bart Hartgers]

Denis Vlasenko wrote:
> On Friday 10 March 2006 05:47, Carlos Munoz wrote:
>> Lee Revell wrote:
> 
> What? You are using log10 only twice!
> 
>         if (!(siu_obj_status & ST_OPEN)) {
> 		...
>                 /* = log2(over) */
>                 ydef[22] = (u_int32_t)(log10((double)(over & 0x0000003f)) /
>                                        log10(2));
> 		...
>         }
>         else {
> 		...
>                 if (coef) {
>                         ydef[16] = 0x03045000 | (over << 26) | (tap - 4);
>                         ydef[17] = (tap * 2 + 1);
>                         /* = log2(over) */
>                         ydef[22] = (u_int32_t)
>                                 (log10((double)(over & 0x0000003f)) / log10(2));
>                 }
> 
> Don't you think that log10((double)(over & 0x0000003f)) / log10(2)
> can have only 64 different values depending on the result of (over & 0x3f)?
> 
> Obtain them from precomputed uint32_t log10table[64].

And since you're actually trying to do log2 [log10(x)/log10(2) =
log2(x)] and casting the result to an integer, aren't you really looking
for the position of the highest 1 bit or something like that? That
doesn't need FP at all.

Groeten,
Bart

> --
> vda
> -
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-- 
Bart Hartgers - TUE Eindhoven - http://plasimo.phys.tue.nl/bart/contact/


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Re: Re: How can I link the kernel with libgcc ?

[James Courtier-Dutton]

Carlos Munoz wrote:
> Lee Revell wrote:
>
>> On Thu, 2006-03-09 at 19:25 -0800, Carlos Munoz wrote:
>>  
>>
>>> I figured out how to get the driver to use floating point operations.
>>> I included source code (from an open source math library) for the
>>> log10 function in the driver. Then I added the following lines to the
>>> file arch/sh/kernel/sh_ksyms.c:   
Carlos,

Be warned. You CANNOT use floating point instructions in the kernel.
The floating point registers are not saved during a task switch for any 
kernel module.

James




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Re: How can I link the kernel with libgcc ?

[Carlos Munoz]

Denis Vlasenko wrote:

>On Friday 10 March 2006 05:47, Carlos Munoz wrote:
>  
>
>>Lee Revell wrote:
>>
>>    
>>
>>>On Thu, 2006-03-09 at 19:25 -0800, Carlos Munoz wrote:
>>> 
>>>
>>>      
>>>
>>>>I figured out how to get the driver to use floating point operations.
>>>>I included source code (from an open source math library) for the
>>>>log10 function in the driver. Then I added the following lines to the
>>>>file arch/sh/kernel/sh_ksyms.c: 
>>>>   
>>>>
>>>>        
>>>>
>>>Where is the source code to your driver?
>>>
>>>Lee
>>>
>>> 
>>>
>>>      
>>>
>>Hi Lee,
>>
>>Be warned. This driver is in the early stages of development. There is 
>>still a lot of work that needs to be done (interrupt, dma, etc, etc).
>>    
>>
>
>What? You are using log10 only twice!
>
>        if (!(siu_obj_status & ST_OPEN)) {
>		...
>                /* = log2(over) */
>                ydef[22] = (u_int32_t)(log10((double)(over & 0x0000003f)) /
>                                       log10(2));
>		...
>        }
>        else {
>		...
>                if (coef) {
>                        ydef[16] = 0x03045000 | (over << 26) | (tap - 4);
>                        ydef[17] = (tap * 2 + 1);
>                        /* = log2(over) */
>                        ydef[22] = (u_int32_t)
>                                (log10((double)(over & 0x0000003f)) / log10(2));
>                }
>
>Don't you think that log10((double)(over & 0x0000003f)) / log10(2)
>can have only 64 different values depending on the result of (over & 0x3f)?
>
>Obtain them from precomputed uint32_t log10table[64].
>--
>vda
>  
>
Hi Denis,

Yes, the driver code so far only uses log10 twice, but there will be 
more uses for it as I populate the rest of the tables. However, I think 
its use will be some what limited. I wasn't aware that the floating 
point registers are not saved. I'll investigate a way to create a table 
with pre-calculated log10 values.

Thanks,


Carlos

Re: How can I link the kernel with libgcc ?

[linux-os (Dick Johnson)]

On Fri, 10 Mar 2006, Carlos Munoz wrote:

> Denis Vlasenko wrote:
>
>> On Friday 10 March 2006 05:47, Carlos Munoz wrote:
>>
>>
>>> Lee Revell wrote:
>>>
>>>
>>>
>>>> On Thu, 2006-03-09 at 19:25 -0800, Carlos Munoz wrote:
>>>>
>>>>
>>>>
>>>>
>>>>> I figured out how to get the driver to use floating point operations.
>>>>> I included source code (from an open source math library) for the
>>>>> log10 function in the driver. Then I added the following lines to the
>>>>> file arch/sh/kernel/sh_ksyms.c:
>>>>>
>>>>>
>>>>>
>>>>>
>>>> Where is the source code to your driver?
>>>>
>>>> Lee
>>>>
>>>>
>>>>
>>>>
>>>>
>>> Hi Lee,
>>>
>>> Be warned. This driver is in the early stages of development. There is
>>> still a lot of work that needs to be done (interrupt, dma, etc, etc).
>>>
>>>
>>
>> What? You are using log10 only twice!
>>
>>        if (!(siu_obj_status & ST_OPEN)) {
>> 		...
>>                /* = log2(over) */
>>                ydef[22] = (u_int32_t)(log10((double)(over & 0x0000003f)) /
>>                                       log10(2));
>> 		...
>>        }
>>        else {
>> 		...
>>                if (coef) {
>>                        ydef[16] = 0x03045000 | (over << 26) | (tap - 4);
>>                        ydef[17] = (tap * 2 + 1);
>>                        /* = log2(over) */
>>                        ydef[22] = (u_int32_t)
>>                                (log10((double)(over & 0x0000003f)) / log10(2));
>>                }
>>
>> Don't you think that log10((double)(over & 0x0000003f)) / log10(2)
>> can have only 64 different values depending on the result of (over & 0x3f)?
>>
>> Obtain them from precomputed uint32_t log10table[64].
>> --
>> vda
>>
>>
> Hi Denis,
>
> Yes, the driver code so far only uses log10 twice, but there will be
> more uses for it as I populate the rest of the tables. However, I think
> its use will be some what limited. I wasn't aware that the floating
> point registers are not saved. I'll investigate a way to create a table
> with pre-calculated log10 values.
>
> Thanks,
>
>
> Carlos

Since the log in base n is the log in any base times a constant,
you can probably use log base 2 (binary bit position) and multiply
the result by a constant, which may simply be shifts and adds.

I assume you are using 16-bit audio. If so, the dynamic range
is only 20 * log10(2^16) = 96.3 dB. That means that attenuation
from mininum to maximum, in 1 dB steps, requires only 94 values.

Your code shows something whacked off at 0x3f = 0->0x40 = 64
20 * log10(64) = 36 dB for only 36 values. Clearly, you don't
need floating point, just some thought ahead of time.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.15.4 on an i686 machine (5589.54 BogoMips).
Warning : 98.36% of all statistics are fiction, book release in April.
_
\x1a\x04

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Re: How can I link the kernel with libgcc ?

[Ben Slusky]

On Fri, 10 Mar 2006 13:33:02 -0500, linux-os (Dick Johnson) wrote:
> 
> On Fri, 10 Mar 2006, Carlos Munoz wrote:
> 
> > Denis Vlasenko wrote:
> >
> >> On Friday 10 March 2006 05:47, Carlos Munoz wrote:
> >>
> >>
> >>> Lee Revell wrote:
> >>>
> >>>
> >>>
> >>>> On Thu, 2006-03-09 at 19:25 -0800, Carlos Munoz wrote:
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>> I figured out how to get the driver to use floating point operations.
> >>>>> I included source code (from an open source math library) for the
> >>>>> log10 function in the driver. Then I added the following lines to the
> >>>>> file arch/sh/kernel/sh_ksyms.c:
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>> Where is the source code to your driver?
> >>>>
> >>>> Lee
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>> Hi Lee,
> >>>
> >>> Be warned. This driver is in the early stages of development. There is
> >>> still a lot of work that needs to be done (interrupt, dma, etc, etc).
> >>>
> >>>
> >>
> >> What? You are using log10 only twice!
> >>
> >>        if (!(siu_obj_status & ST_OPEN)) {
> >> 		...
> >>                /* = log2(over) */
> >>                ydef[22] = (u_int32_t)(log10((double)(over & 0x0000003f)) /
> >>                                       log10(2));
> >> 		...
> >>        }
> >>        else {
> >> 		...
> >>                if (coef) {
> >>                        ydef[16] = 0x03045000 | (over << 26) | (tap - 4);
> >>                        ydef[17] = (tap * 2 + 1);
> >>                        /* = log2(over) */
> >>                        ydef[22] = (u_int32_t)
> >>                                (log10((double)(over & 0x0000003f)) / log10(2));
> >>                }
> >>
> >> Don't you think that log10((double)(over & 0x0000003f)) / log10(2)
> >> can have only 64 different values depending on the result of (over & 0x3f)?
> >>
> >> Obtain them from precomputed uint32_t log10table[64].
> >> --
> >> vda
> >>
> >>
> > Hi Denis,
> >
> > Yes, the driver code so far only uses log10 twice, but there will be
> > more uses for it as I populate the rest of the tables. However, I think
> > its use will be some what limited. I wasn't aware that the floating
> > point registers are not saved. I'll investigate a way to create a table
> > with pre-calculated log10 values.
> >
> > Thanks,
> >
> >
> > Carlos
> 
> Since the log in base n is the log in any base times a constant,
> you can probably use log base 2 (binary bit position) and multiply
> the result by a constant, which may simply be shifts and adds.
> 
> I assume you are using 16-bit audio. If so, the dynamic range
> is only 20 * log10(2^16) = 96.3 dB. That means that attenuation
> from mininum to maximum, in 1 dB steps, requires only 94 values.
> 
> Your code shows something whacked off at 0x3f = 0->0x40 = 64
> 20 * log10(64) = 36 dB for only 36 values. Clearly, you don't
> need floating point, just some thought ahead of time.
> 
> Cheers,
> Dick Johnson

As Bart pointed out earlier, what this code is really trying to do is not
log10(foo) but int(log2(foo)) for some positive integer foo. This can be
simply expressed as fls(foo)-1 for all foo < 0. No floating point
necessary.

-- 
Ben Slusky                      | Trust is your enemy.
sluskyb@paranoiacs.org          |       -Dan Farmer and
sluskyb@stwing.org              |        Wietse Venema
PGP keyID ADA44B3B      

Re: How can I link the kernel with libgcc ?

[Al Viro]

On Fri, Mar 10, 2006 at 10:03:58AM -0800, Carlos Munoz wrote:
> >               ydef[22] = (u_int32_t)(log10((double)(over & 0x0000003f)) /
> >                                      log10(2));

You've got to be kidding.  Let's take a good look at that expression:
log10(x)/log10(2) is what?  Right, base-2 logarithm of x.  Then you cast
it to unsigned, i.e. round it down.  In other words, you want to know the
highest bit in (over & 0x3f).  Which is to say, (fls(over & 0x3f) - 1).
Sigh...

Re: How can I link the kernel with libgcc ?

[Carlos Munoz]

Al Viro wrote:

>On Fri, Mar 10, 2006 at 10:03:58AM -0800, Carlos Munoz wrote:
>  
>
>>>              ydef[22] = (u_int32_t)(log10((double)(over & 0x0000003f)) /
>>>                                     log10(2));
>>>      
>>>
>
>You've got to be kidding.  Let's take a good look at that expression:
>log10(x)/log10(2) is what?  Right, base-2 logarithm of x.  Then you cast
>it to unsigned, i.e. round it down.  In other words, you want to know the
>highest bit in (over & 0x3f).  Which is to say, (fls(over & 0x3f) - 1).
>Sigh...
>  
>
Hi Al,

You are right, so easy. I will look at the data sheet and make sure the 
same approach can be applied to all places calling for log10 
calculations. I wonder why the data sheet calls for log10 calculations. 
It threw me off... should have know better though.

Thanks,


Carlos Munoz