On Fri, Mar 13, 2009 at 5:11 PM, Trent Piepho <xyzzy@xxxxxxxxxxxxx> wrote: > I like 8.8 fixed point a lot better. It gives more precision. The range > is more in line with that the range of real SNRs are. Computers are > binary, so the math can end up faster. It's easier to read when printed > out in hex, since you can get the integer part of SNR just by looking at > the first byte. E.g., 25.3 would be 0x194C, 0x19 = 25 db, 0x4c = a little > more than quarter. Several drivers already use it. Wow, I know you said you like that idea alot better, but I read it and it made me feel sick to my stomach. Once we have a uniform format, we won't need to show it in hex at all. Tools like femon and scan can just show the value in decimal (they show it in hex because it's definition varies by device). Target applications can reformat the value any way you prefer. This is a kernel interface. On a separate note, do you know specifically which drivers use that format? I was putting together a table of all the various demodulators and which format they use, so if you have demods you know about I would be interested in filling out that data. >> 2. Getting everyone to agree on the definition of "Strength". Is >> this the field strength? Is this some coefficient of the SNR compared >> to an arbitrary scale? Is it a percentage? If it's a percentage, is >> it 0-100 or 0-65535? > > The problem with strength is that practically no hardware can measure true > signal strength. I'm fine being a little more flexible on the definition of "strength", as long as the resulting value is presented in a uniform format. While SNR should have a strict definition, I'm fine with having strength being something like "0-100%, scaled up to 0xffff". For drivers that only have SNR, they can just scale up the SNR based on a fixed maximum (some ATSC drivers for example, consider 35 dB to be 100%). Or drivers that have field strength measuring capabilities can return that value. In my mind, the goal isn't being able to compare different devices between each other, so much as being able to get a uniform way for users to know about what the signal quality is. I want users of Kaffeine to be able to go to the signal monitor section and see the "strength" indicator show a value from 0-100%, regardless of which device they are using. Certainly though, I want to get enough logic in there for devices to be able to indicate that the driver does not support returning the value (instead of returning zero), and be able to indicate that it cannot return the valid value right now (for example, many chips cannot return a valid value when there is no signal lock). Devin -- Devin J. Heitmueller http://www.devinheitmueller.com AIM: devinheitmueller -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
