Re: [Qemu-devel] [RFC][PATCH 4/4] Add support for Marvell 88w8618 / MusicPal

[andrzej zaborowski]

On 17/04/2008, andrzej zaborowski <address@hidden> wrote:
>  On 13/04/2008, Jan Kiszka <address@hidden> wrote:
>  > This is the board emulation for Freecom's MusicPal, featuring
>  >   - rudimentary PIT and PIC
>  >   - up to 2 UARTs
>  >   - 88W8xx8 Ethernet controller
>  >   - 88W8618 audio controller
>  >   - Wolfson WM8750 mixer chip (volume control and mute only)
>
> Are you sure that hw/wm8750.c is not reusable?  It's probably better
>  to extend it with volume control, and audio data transmission through
>  i2c, instead of having two implementations in QEMU.
>
>  Regarding volume control, since there are only 0x7f possible values
>  it's nicer to use a const table than pull in math.h.  Actually I
>  wouldn't worry about that at all because the layout of volume levels
>  on the host is not guaranteed to be linear (I think?), it may very
>  well be already exponential.  For example the Linux WM8750 driver
>  doesn't do the reverse transformation which would mean that on a host
>  whose ALSA output device is a WM8750, the Qemu vm would have a wrong
>  volume scale.

Ah, we're multiplying the samples, rather than setting volume on host.
 Please ignore the above comment, but it would still be good to avoid
pow() (especially if return value is invariant across the loop and
perhaps across many buffer fills).
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