linux-kernel - Re: [PATCH v3 3/9] media: adv7180: add support for NEWAVMODE

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Message-ID: <153fdfbc-a929-6584-3f06-26413498c1fa@gmail.com>
Date:	Mon, 25 Jul 2016 23:24:51 +0100
From:	Ian Arkver <ian.arkver.dev@...il.com>
To:	Steve Longerbeam <steve_longerbeam@...tor.com>,
	Steve Longerbeam <slongerbeam@...il.com>, lars@...afoo.de
Cc:	mchehab@...nel.org, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/9] media: adv7180: add support for NEWAVMODE

On 25/07/16 23:04, Steve Longerbeam wrote:
>
>
> On 07/25/2016 12:36 PM, Ian Arkver wrote:
>> On 25/07/16 18:55, Steve Longerbeam wrote:
>>> On 07/25/2016 05:04 AM, Ian Arkver wrote:
>>>> On 23/07/16 18:00, Steve Longerbeam wrote:
>>>>> <snip>
>>>>> +#define ADV7180_VSYNC_FIELD_CTL_1_NEWAVMODE 0x02
>>>> See below re this value.
>>>>
>>> Hi Ian, I double-checked the ADV7180 datasheet, this value is
>>> correct. Bit 4, when cleared, _enables_ NEWAVMODE.
>>
>> Hah, ok. I'm not familiar enough with the history of this chip and 
>> didn't
>> know what "OLDAVMODE" was. So, to enable NEWAVMODE you clear
>> the NEWAVMODE bit. That makes perfect sense.
>>
>> Anyway, I still don't see what NEWAVMODE gets you.
>
> Hi Ian,
>
> With video standard auto-detect disabled in the chip (VID_SEL > 2), 
> captured NTSC
> images by the i.mx6q SabreAuto are corrupted, best I can describe it 
> as "extremely
> fuzzy". Only when newavmode is enabled do the images look good again, 
> in manual
> mode. With auto-detect enabled, images look good with or without 
> newavmode.
>
> The strange this is, the auto-detected standard is identical to the 
> standard set
> explicitly in manual mode (NTSC-M). I did a complete i2c dump of the 
> registers
> for both auto-detect and manual mode, and found no other differences 
> besides
> the auto-detect/manual setting.
>
> Trying to track this down further would probably require a logic 
> analyzer on the
> bt.656 bus, which I don't have access to.
>
> I will not be debugging this further so NEWAVMODE it will have to remain.
>
> Steve

OK, interesting. And weird indeed.

I may be interfacing an ADV7280 to the i.MX6 in the August timeframe, 
depending on
project needs etc. I'll see if I hit this with that chip. My test app 
does use autodetect.

Incidentally, looking at the BT656-5 spec and comparing to the tvp5150, 
I see that
the spec calls for 244 and 243 lines per field for NTSC, and the tvp5150 
provides
that number of lines. However this write...

adv7180_write(state, ADV7180_REG_NTSC_V_BIT_END,
             ADV7180_NTSC_V_BIT_END_MANUAL_NVEND);

where NVEND is 0x4f, configures the adv7180 to send only 242 lines in 
each field.
Not sure if this is significant.

Regards,
IanJ.

>
>> As
>> far as I can see it just locks down the timings and removes the 
>> flexibility
>> the chip otherwise offers to move the BT656 SAV and EAV codes around
>> relative to the incoming video.
>>
>> In what circumstances would you need to set the newavmode property
>> and change this default behaviour? We're not coupling the adv7180
>> back-to-back with an ADV video encoder here, which is what
>> NEWAVMODE is for and is presumably why AD recommend it for their
>> eval boards. We're trying to get a BT656 compliant stream, which is
>> what the default mode purports to generate.
>>
>> Regards,
>> IanJ
>>
>
>