highaltitude.log.20090202

[00:49] <SpeedEvil> http://dealextreme.com/details.dx/sku.17873 Balloons!
[00:49] <SpeedEvil> :)
[00:56] <Laurenceb> http://uk.youtube.com/watch?v=qqXi8WmQ_WM
[01:17] <SpeedEvil> Okaaay.
[01:21] <Laurenceb> I like his everyday normal guy one better
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[02:21] <Laurenceb> MFSK is complicated :-/
[02:21] <Laurenceb> it looks to be considerably better than dominoex
[02:21] <shellevil> OFDM!
[02:21] <Laurenceb> not possible
[02:21] <Laurenceb> with our hardware unfortunately
[02:22] <Laurenceb> I would if I could
[02:22] <shellevil> It's just FM?
[02:22] <Laurenceb> yes
[02:22] <shellevil> I mean - the transmitter
[02:22] <Laurenceb> radiometrix fm modules
[02:22] <Laurenceb> with pwm input
[02:22] <Laurenceb> so you can generate one frequency at a time
[02:23] <Laurenceb> in other words
[02:23] <Laurenceb> I'm working on MFSK but its tricky - interleaving and FEC
[02:23] <Laurenceb> also it uses varicode
[02:24] <shellevil> Why do you need the last amount of bitrate?
[02:25] <shellevil> What're you transmitting down?
[02:25] <Laurenceb> position, heading ect
[02:25] <Laurenceb> but it has to be compatible with the mfsk protocol
[02:26] <Laurenceb> which uses concatenated interleavers and FEC
[02:29] <shellevil> do you actually react to this data in realtime, or is it simply for logging?
[02:29] <Laurenceb> just for logging
[02:29] <Laurenceb> there will be a few seconds latency
[02:32] <shellevil> http://en.wikipedia.org/wiki/Olivia_MFSK ?
[02:34] <Laurenceb> I'm not going to those lenghts
[02:37] <shellevil> Hmm.
[02:37] <shellevil> The above actually seems like something that might get through GSM codecs
[02:43] <Laurenceb> with olivia I'm limited to about 5cps
[02:44] <Laurenceb> not high enough
[02:44] <Laurenceb> I can get about 15 with MFSK
[02:46] <shellevil> mfsk is a general term - what implementation?
[02:46] <shellevil> why isn't 5 high enough - or do you want text?
[02:47] <shellevil> Annoyingly many of the olivia links are broken
[02:47] <shellevil> including the source link :/
[02:49] <Laurenceb> MFSK64
[02:49] <Laurenceb> 16FSK, 64baud
[02:55] <Laurenceb> http://www.qsl.net/zl1bpu/MFSK/tx.htm
[02:55] <Laurenceb> I'll do the first 3 stages in the Rx ISR
[02:55] <Laurenceb> then shove into a buffer
[02:56] <Laurenceb> then a time ISR does the interleaving and tx frequency control
[02:56] <Laurenceb> so it interleaves from the buffer
[02:59] <shellevil> sounds interesting
[03:01] <Laurenceb> everything operates at the bit level, so it means lots of bit shifting operators required
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[04:20] <Laurenceb> http://pastebin.com/d692cdc76
[04:20] <Laurenceb> thats what I've got so far
[04:20] <Laurenceb> problem is it needs to support the idle mode properly
[04:21] <Laurenceb> so I may be better having the buffer hold incoming ascii, then the main code is free to set/unset idle mode according to the state of the buffer
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[09:22] <rjharrison> Morning all
[09:22] <rjharrison> Anyone got some of the white stuff
[09:25] <gordonjcp> a wee bit
[09:42] <rjharrison> Need to prey to the weather gods for a launch this w/e
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[09:51] <jcoxon> lots of snow here
[09:51] <jcoxon> nothing is working
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[11:02] Action: shellevil had 3" or so last he looked at 9.
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[11:09] <rjharrison> Quick call to CUSF members is BADGER keeping the same sentence structure as last launch?
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[11:15] <rjharrison> M0TEK: is BADGER keeping the same sentence structure as last launch?
[11:16] <rjharrison> jcoxon: Enforced day off for you in London?
[11:16] <jcoxon> sort of
[11:16] <jcoxon> lack of buses make it impossible to get to hospital
[11:16] <jcoxon> well i could walk but that would take ages
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[11:16] <jcoxon> luckily i'm all kitted out for snow after norway
[11:16] <rjharrison> So a bit of habing then instead
[11:16] <jcoxon> so am ruling the snowball fights
[11:16] <rjharrison> hehe
[11:17] <jcoxon> the only one with snow boots in bermondsey
[11:21] <M0TEK> rjharrison: don't know yet
[11:21] <M0TEK> probably
[11:21] <M0TEK> unless we decide to add stuff
[11:21] <M0TEK> infact no, of course not
[11:21] <M0TEK> won't need 5 tempertures
[11:27] <rjharrison> Great
[11:28] <rjharrison> It would be really helpfull to get a few sentances off badger just before the next launch to set the listener up correctly
[11:28] <M0TEK> not a prob
[11:29] <rjharrison> If the weather is good I'm hoping to launch next w/e
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[12:32] <rjharrison> Yippee
[12:32] <rjharrison> Schools been closed
[12:32] <rjharrison> Have to go and get the kids and build snowmen
[12:33] <rjharrison> Uni should be fun for you guys tonight. We had some mental snowball fights betweeen the houses when it snowed in Leeds
[12:35] <rjharrison> Just when you think you're too old to throw snowballs, some bugger lanches one at you and all hell breaks lose. In fact I remember some idiot warden coming out at 3 in the morning telling us to go to bed or else and he got or else in about 600 snowballs
[12:37] <rjharrison> BTW I got 16th on the world balloon records
[12:40] <jcoxon> oh nice, you submitted it
[12:41] <rjharrison> yep they were cool
[12:42] <rjharrison> just wanted proof of log and that i had licence ham
[12:46] <rjharrison> ttfn
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[18:02] <Laurenceb> hello
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[18:14] <Laurenceb> hi rob
[18:18] Action: Laurenceb has been in A&E all day :-(
[18:20] <shellevil> :/
[18:20] <Laurenceb> I got attacked by chavs
[18:20] <shellevil> Ballooning accident?
[18:20] <shellevil> eww.
[18:21] <Laurenceb> was walking over a motorway bridge and there were 4 of them dropping rocks onto cars
[18:21] <Laurenceb> obviously I tried to stop them but there were 4 of them
[18:21] <shellevil> need done for attempted murder - for that. :/
[18:22] <Laurenceb> well I've reported it to the police
[18:22] <Laurenceb> but they hardly seemed interested
[18:22] <shellevil> badly wounded?
[18:22] <Laurenceb> I've got some nasty cuts to the face
[18:22] <Laurenceb> had to have an x ray
[18:23] <Laurenceb> my vision went really bad but its ok now
[18:23] <shellevil> damn.
[18:23] <Laurenceb> yeah
[18:23] <shellevil> At least something to be thankfull for - in a shitty mess.
[18:24] <Laurenceb> maybe I should have ignored them but what can you do
[18:25] <shellevil> Bring back national service! Or something. I have absolutely no idea of a proper solution. If only everything were solvable with maths.
[18:25] <Laurenceb> at least they ran off after smacking me in the face several times, so no drivers got injured
[18:26] <Laurenceb> hopefully they were caught on cctv
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[18:28] <Laurenceb> they have some groovy kit in A&E these days
[18:28] <Laurenceb> luckyl its a while since I last visited :P
[18:29] <shellevil> If more people diddn't ignore them, it'd probably get better. But - positive feedback :/
[18:30] <shellevil> ages?
[18:30] <shellevil> (of the chavs)
[18:30] <natrium42> :/
[18:30] <Laurenceb> ~16
[18:30] <natrium42> seriously, too many bystanders not willing to do anything :/
[18:31] <natrium42> major props, Laurenceb
[18:32] <Laurenceb> thanks
[18:33] <shellevil> Indeed.
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[18:43] <natrium42> shellevil: was it you who ordered one of those spy pens from DX?
[18:43] <Laurenceb> you pervert you
[18:43] <natrium42> XD
[18:43] <natrium42> i ordered two also
[18:43] <natrium42> Laurenceb: they got 4GB and can do continuous video recording
[18:44] <natrium42> very useful to monitor systems for a launch
[18:44] <natrium42> i.e. balloon burst, drop mechanism
[18:45] <Laurenceb> neat
[18:45] <natrium42> http://www.dealextreme.com/details.dx/sku.18088
[18:45] <Laurenceb> might get one for the rogallo
[18:45] <natrium42> yeah
[18:45] <natrium42> i forgot to order a fisheye lens for it :S
[18:46] <natrium42> they have a neat one which gives 160 degrees
[18:53] <Laurenceb> wow thats nice
[18:53] <Laurenceb> 2 hours life
[18:54] <Laurenceb> looks perfect for sticking on the front of the mini rogallo
[18:56] <natrium42> don't have to use internal battery -- i am more interested on how much video would fit onto 4GB flash
[18:57] <Laurenceb> yeah just right it up to the rail on the payload
[18:57] <Laurenceb> http://uk.youtube.com/watch?v=15S0g8pG6HU <-- to go with your pervert cam
[18:58] <natrium42> LOL
[18:58] <natrium42> eww
[18:59] <Laurenceb> just need to add that camera
[19:00] <shellevil> nat: yes
[19:00] <shellevil> not here yet
[19:01] <Laurenceb> guess theres a single pcb in there
[19:01] <Laurenceb> maybe with a lipo down the side
[19:06] <shellevil> a comment alluded to a cylindrical cell
[19:07] <Laurenceb> odd
[19:08] <Laurenceb> you'd expect lipo
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[19:17] <Laurenceb> fergusnoble: ping
[19:17] <natrium42> shellevil: did they ship yours yet?
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[19:17] <shellevil> not yet
[19:18] <shellevil> lipo doesn't work so well with minimum dimension at 12mm or so
[19:18] <Laurenceb> maybe nimh
[19:18] <shellevil> the case seals take up a lot of space
[19:18] <shellevil> I've got some 10180 cells
[19:19] <Laurenceb> what are those?
[19:19] <shellevil> 10mm dia*18mm
[19:19] <shellevil> 1/3AAA Li-ion
[19:19] <Laurenceb> interesting
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[19:22] Action: Laurenceb is still trying to work out how MFSK interleavng works
[19:23] <jcoxon> evening all
[19:23] <Laurenceb> hi jcoxon
[19:24] <jcoxon> hey Laurenceb
[19:25] <jcoxon> just read about the chavs - hope you are okay
[19:26] <Laurenceb> yeah not too bad thanks
[19:29] <jcoxon> hmmm my gps module interferes with my radio
[19:29] Bluenarf (n=Paul@apollo.paulsnet.org) got netsplit.
[19:29] <jcoxon> at about a 1Hz
[19:30] <jcoxon> so guess its the serial
[19:40] Bluenarf (n=Paul@apollo.paulsnet.org) got lost in the net-split.
[19:40] <Laurenceb> http://sharon.esrac.ele.tue.nl/mirrors/zl1bpu/MFSK/Interleaver.html
[19:41] <Laurenceb> can anyone help me understand?
[19:41] <Laurenceb> I just dont get it
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[19:44] <Laurenceb> what do they mean by 10 interleavers?
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[19:59] <jcoxon> Laurenceb, not sure sorry
[19:59] <jcoxon> any idea how i can reduce the interference on the radio from the gps module?
[20:00] <Laurenceb> what sort of interference?
[20:02] <Laurenceb> maybe th epower line?
[20:02] <jcoxon> there is a sort of buzz at 1hz
[20:02] <jcoxon> when the gps is powered on
[20:03] <Laurenceb> maybe something to do with the processor
[20:03] <Laurenceb> wht sort of modu;e?
[20:03] <jcoxon> ublox tim-lf
[20:04] <Laurenceb> you wouldnt expect the serial to interfere
[20:04] <Laurenceb> but I dont think it has external ram
[20:04] <Laurenceb> maybe it somehow puts noise onto the power rails
[20:04] <Laurenceb> try some cpa
[20:04] <Laurenceb> s*caps
[20:07] <jcoxon> good plan
[20:07] <natrium42> hi jcoxon
[20:09] <jcoxon> hey natrium42
[20:09] <jcoxon> we have snow!
[20:09] <jcoxon> and the infrastructure has collapsed :-p
[20:16] <Laurenceb> theres about 18" here
[20:25] <natrium42> jcoxon: haha
[20:25] <natrium42> you have no infrastructure to deal with snow apparently :P
[20:26] <Laurenceb> http://homepage.mac.com/chen/Technical/cocoaModem/Implementation/MFSK16/Interleaver/index.html
[20:27] <Laurenceb> ok... I think I get it
[20:27] <Laurenceb> so you have a 164 element buffer ... ?
[20:35] <Laurenceb> latency? must be that damn interleaving again
[20:41] <rjharrison> evening all
[20:41] <rjharrison> Kid duties done
[20:41] <Laurenceb> can you bit shift by a negative number in c ?
[20:41] <Laurenceb> :P
[20:41] <rjharrison> Humm
[20:41] <rjharrison> What do you want to achive
[20:42] <rjharrison> You can shift left an right
[20:42] <jcoxon> evening rjharrison
[20:42] <rjharrison> hi jcoxon
[20:42] <rjharrison> London still frozen
[20:42] <rjharrison> It's out turn tonight
[20:42] <jcoxon> indeed
[20:43] <Laurenceb> antifreeze carpetbombing
[20:43] <jcoxon> oh it'll be fine tomorrow
[20:44] <fergusnoble> Laurenceb: hello
[20:44] <Laurenceb> hi fergus
[20:44] <Laurenceb> I was goig to ask you about this board
[20:45] <Laurenceb> what are you aiming to do?
[20:45] <Laurenceb> - SE4120 board
[20:45] <fergusnoble> which board?
[20:45] <fergusnoble> oh right, was planning on putting the output in parallel to both the blackfin and an lpc2368
[20:46] <fergusnoble> the lpc writes it raw to the sd card
[20:46] <fergusnoble> the blackfin does the decode and pics and also tells the lpc to write that to the sd card
[20:46] <fergusnoble> maybe some accelerometers too, dont know
[20:46] <fergusnoble> certainly not a full imu or anything though
[20:47] <Laurenceb> neat
[20:47] <fergusnoble> the lpc has a proper sd interface that can write 5MB/s
[20:47] <Laurenceb> sounds good
[20:47] <Laurenceb> we're working on something similar for atmospheric work
[20:47] <fergusnoble> how were you planning to do it?
[20:48] <Laurenceb> using DDR3
[20:49] <Laurenceb> and a maxim DVBT receiver as the front end
[20:49] <fergusnoble> oh cool
[20:50] <fergusnoble> with an fpga or something?
[20:50] <Laurenceb> yeah
[20:50] <Laurenceb> proasic 3
[20:51] <Laurenceb> fergusnoble: do you understand that interleaving explanation?
[20:51] <Laurenceb> I'm still a bit confused
[20:51] <Laurenceb> you have 164 locations in the buffer?
[20:51] <Laurenceb> http://homepage.mac.com/chen/Technical/cocoaModem/Implementation/MFSK16/Interleaver/index.html
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[21:19] <rjharrison> Hi steve
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[21:25] <Laurenceb> http://pastebin.com/m1b5bc982
[21:25] <Laurenceb> I think thats does the job...
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[21:40] <RocketBoy> fergusnoble: I said lattice coding yesterday - i meant trellis coding (re dominoex coding)
[21:41] <fergusnoble> RocketBoy: ok, isnt that only used in the FEC version though?
[21:42] <Laurenceb> ooh god
[21:42] <Laurenceb> mfsk16 is enoug for me atm
[21:42] <Laurenceb> although most of the problem is the poor documentation
[21:43] <fergusnoble> Laurenceb: use the fldigi code :) thats what open source is for
[21:43] <Laurenceb> i cant follow it
[21:44] <Laurenceb> the fec is rather convoluted
[21:44] <Laurenceb> no pun intended
[21:45] <fergusnoble> RocketBoy: i guess the varicode and tone mapping could be written out as a trellis code but at least in fldigi they do it just cusing modulo artihmetic
[21:46] <Laurenceb> mfsk appears to have higher noise teleranc than dominoex
[21:46] <Laurenceb> hence why I'm working on it
[21:46] <RocketBoy> fergusnoble: yes probably the trellis coding idea added parity bit(s)
[21:46] <Laurenceb> hi jatkins
[21:47] <RocketBoy> not sure if that was to ensure space between symbols or just error correction or both.
[21:49] <jatkins> hi
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[22:07] <jatkins> g2g. bb2moz
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[22:23] <natrium42> ?
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[22:24] <hallam> hi all
[22:24] <hallam> fergusnoble: GPS code runs on the blackfin
[22:24] <natrium42> hey hallam
[22:25] <fergusnoble> hallam: sweet
[22:25] <fergusnoble> you still coming over?
[22:25] <hallam> not sure, maybe
[22:25] <hallam> haven't implemented the hand-coded assembler inner loop yet, but it's giving 40MHz/channel with plain C
[22:25] <fergusnoble> dont worry if your already stuck into work
[22:25] <fergusnoble> awesome :)
[22:25] <hallam> how is your work going?
[22:26] <fergusnoble> its going ok
[22:26] <fergusnoble> slowly getting to grips with variational ethods
[22:26] <fergusnoble> they are cool
[22:26] <Laurenceb> omg
[22:26] <Laurenceb> hallam you are god
[22:27] <Laurenceb> :P
[22:27] <Laurenceb> hallam: how ar eyou tsting it?
[22:27] <fergusnoble> hallam: so thats just running off random data, whatevers in ram?
[22:27] <fergusnoble> or are you loading in some test data?
[22:27] <hallam> just running it with random data
[22:28] <hallam> but the speed should be deterministic
[22:28] <Laurenceb> nice
[22:28] <hallam> I might see if I can load 4MB of data onto the flash and not have to reload it every time I reprogram
[22:28] <Laurenceb> over serial?
[22:29] <Laurenceb> JTAG?
[22:29] <hallam> wifi, then 2.3Mbaud serial
[22:29] <Laurenceb> oh yeah is there a wifi module?
[22:29] <hallam> off the main board
[22:29] <Laurenceb> neat
[22:29] <hallam> won't be on the rocket
[22:29] <Laurenceb> hehe
[22:30] <hallam> useful for robots and for testing
[22:30] <Laurenceb> yeah
[22:30] <Laurenceb> I was thinking of adding an interface socket in my sampler
[22:31] <Laurenceb> - no it neatly
[22:31] <Laurenceb> *do
[22:31] <Laurenceb> hallam: you could still go for the alternative approach of an FPGA and arm
[22:32] <hallam> I'm enjoying the blackfin
[22:32] <Laurenceb> yeah
[22:32] <fergusnoble> Laurenceb: we need the blackfin for the camera anyway
[22:32] <hallam> let me know if you figure out a nice way to do an interface socket
[22:32] <hallam> it shouldn't be too hard
[22:32] <Laurenceb> good point
[22:32] <fergusnoble> so might as well do the gps too
[22:32] <Laurenceb> yeah
[22:32] <Laurenceb> I was just thinking power
[22:32] <Laurenceb> but the blackfin is quite nice
[22:32] <Laurenceb> power wise
[22:33] <hallam> I'll be surprised if the whole of the GPS ends up using more than about 30% cpu
[22:33] <hallam> and most of that will be acquisition
[22:33] <Laurenceb> hallam: I'll use a 0.1" socket from toby.co.uk
[22:33] <hallam> Laurenceb: do you have wire wrap wire?
[22:33] <Laurenceb> no
[22:34] <hallam> you'll want some
[22:34] <Laurenceb> was going to use ribbon cable
[22:34] <hallam> ugh
[22:34] <Laurenceb> hehe
[22:34] <hallam> so much easier with wire wrap / kynar
[22:34] <hallam> just order a small roll of it, it'll last ages
[22:34] <Laurenceb> ok, rapid?
[22:34] <hallam> it really is wonderful stuff
[22:34] <hallam> worth a try
[22:34] <Laurenceb> I'll have to put together an order
[22:35] <hallam> last time I bought some I just googled for kynar wire and there were a couple of places in the UK that sold it
[22:35] <Laurenceb> ok
[22:35] <hallam> rapid might have some though
[22:35] <Laurenceb> yeah
[22:36] <Laurenceb> I'm working on some MFSK16 Tx code atm
[22:37] <Laurenceb> hopefully will improve on rtty
[22:37] <Laurenceb> are you just going to save jpegs from the camera?
[22:38] <hallam> not sure yet
[22:38] <hallam> if I can get the code from Analog, I'll use their MJPEG encoder
[22:38] <hallam> the JPEG encoder I have is really slow
[22:39] <Laurenceb> cool
[22:39] <Laurenceb> they have opensource code?
[22:41] <hallam> don't know yet
[22:42] <hallam> they give it away with VisualDSP I think, I don't know what the license is
[22:42] <Laurenceb> oh is it one of those weird built into the compiler jobs?
[22:43] <Laurenceb> just thinking of fpga tools
[22:43] <Laurenceb> I hate things like that
[22:45] <Laurenceb> ISE has loads of "black box" functions you can just add in
[22:49] <fergusnoble> hallam: it looks like you can use the barrel shifter in parallel to the two alus!
[22:49] <fergusnoble> ie. 3 instructions/cycle for some parts!
[22:50] <Laurenceb> remind me what a barrel shifter does
[22:50] Action: Laurenceb fails
[22:51] <Laurenceb> doh ok
[22:52] <fergusnoble> hallam: if we go for an rtos it should be this one
[22:52] <fergusnoble> http://en.wikipedia.org/wiki/RTEMS
[22:52] <fergusnoble> "Real-Time Executive for Missile Systems" :)
[22:52] <Laurenceb> haha
[22:53] <hallam> heh, nice
[22:53] <hallam> fergusnoble: interesting, where did you read about that? (the barrel)
[22:54] <fergusnoble> the best of all sources
[22:54] <Laurenceb> lol its open source as well
[22:54] <hallam> PRM?
[22:54] <fergusnoble> wikipedia
[22:54] <Laurenceb> wonder what stallman has to say
[22:54] <fergusnoble> :)
[22:54] <Laurenceb> not suite what he had in mind
[22:54] <Laurenceb> *quite
[22:54] <hallam> I managed to extract the files from the jpeg encoder archive but it's just a binary library, and an evaluation version at that (limited picture size, prints a watermark)
[22:55] <Laurenceb> that would suck
[22:56] <hallam> yeah it's a pity
[22:56] <hallam> I guess I can try to get the existing encoder running a bit faster
[22:57] <fergusnoble> or we could just take still frames?
[22:57] <Laurenceb> you have to run 2D FFTs for jpeg
[22:57] <fergusnoble> video would be nice though
[22:57] <Laurenceb> or are there faster ways?
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[23:00] <fergusnoble> you use a DCT not an FFT which saves you half
[23:01] <fergusnoble> and also has the effect you loose data at the high end of the spectrum first
[23:01] <hallam> we can probably capture about 5fps continuously with the existing encoder unmodified
[23:02] <hallam> or full rate at 320x240
[23:02] <fergusnoble> how large is a frame when compressed?
[23:02] <hallam> adjustable, but around 40kB IIRC for 640x480
[23:02] <fergusnoble> hallam: maybe try enabling write-back cacheing and see if that helo
[23:02] <fergusnoble> *helps
[23:02] <hallam> already did, little difference
[23:02] <fergusnoble> ok
[23:03] <fergusnoble> could you try and make it so all its variables will fit in the cache?
[23:03] <hallam> after all it's reading half a megabyte, and writing less than 1/10 that
[23:03] <fergusnoble> yeah, sure, makes sense
[23:03] <hallam> I think they do, not sure though
[23:03] <hallam> I think it's all in L1 at the moment apart from the input and output buffers
[23:03] <fergusnoble> ok, cool
[23:04] <hallam> maybe rewrite the tightest part in asm
[23:04] <hallam> although I think the DCT already is
[23:04] <Laurenceb> how does the cache work? do you see it from the code?
[23:04] <fergusnoble> maybe profile it and then look at those areas first
[23:04] <hallam> yeah
[23:04] <fergusnoble> you can profile it on the pc i guess
[23:04] <hallam> Laurenceb: not really
[23:04] <Laurenceb> as in if you use more ram, do you just move up out of the cache?
[23:04] <hallam> er
[23:04] <hallam> well there's L1 memory
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[23:04] <hallam> and external SDRAM
[23:04] <Laurenceb> yeah
[23:05] <hallam> you can put stuff straight in L1 or SDRAM
[23:05] <hallam> you can also assign part of the L1 to automatically cache the SDRAM
[23:05] <Laurenceb> jright
[23:05] <hallam> if it's assigned as cache, you can't directly address it
[23:05] <Laurenceb> so you can have L1 and SDRAM as one address space or L1 as cache?
[23:06] <Laurenceb> or some combination of those two
[23:06] <fergusnoble> Laurenceb: its all one address space
[23:06] <Laurenceb> even with cache?
[23:06] <fergusnoble> but you can just set the cpu to pull things into the cache as you read them from sdram
[23:06] <Laurenceb> right
[23:07] <Laurenceb> and how is the cache managed?
[23:07] <fergusnoble> yeah, but you'd never access the cache directly, in fact that may just cause an exception
[23:07] <Laurenceb> so its handled by the processor?
[23:07] <hallam> CPLBs
[23:07] <hallam> yeah
[23:07] <fergusnoble> its built into the memory manager
[23:07] <hallam> you set it up but after that it's pretty transparent
[23:07] <Laurenceb> you just acess your data - end of ?
[23:07] <hallam> right
[23:07] <fergusnoble> you just tell it which areas of memory you want to be cacheable
[23:07] <Laurenceb> ok
[23:07] <Laurenceb> cool
[23:08] <Laurenceb> if you have an os like say linux running, do you use the mmu to create a seperate address space for each task?
[23:10] <fergusnoble> Laurenceb: no you cant change the memory mapping
[23:10] <fergusnoble> but there is some limited memory protection
[23:10] <fergusnoble> there is a user and supervisor mode
[23:10] <Laurenceb> say I have my ngw100/gumstix running, I can just copy over some binary and run it
[23:10] <Laurenceb> how does that work?
[23:10] <fergusnoble> what do you mean?
[23:11] <Laurenceb> well it was compiled with no knowledge of the memory structure
[23:11] <Laurenceb> it was compiled seperately from the os
[23:11] <hallam> yeah the blackfin doesn't have virtual memory
[23:11] <Laurenceb> oh thats virtual memory
[23:11] <Laurenceb> ok
[23:11] <hallam> I think so
[23:11] <hallam> I've only learned about this stuff pretty recently
[23:12] <Laurenceb> I think i understand now
[23:12] <Laurenceb> this has always confused me :P
[23:12] <fergusnoble> thats not specifically virtual memory, but is an example of
[23:12] <hallam> I think the kernel could do something equivalent in software
[23:12] <Laurenceb> that would surely lead to loads of overheads
[23:12] <fergusnoble> on a cpu with a better mmu you can change the memory mapping on a per process basis
[23:13] <Laurenceb> oh hence uClinux ?
[23:13] <hallam> right, I think so
[23:13] <Laurenceb> ok i get it
[23:13] <hallam> not necessarily crazy overheads, definitely some
[23:13] <fergusnoble> so what the os does is make each application run in its own address space starting from zero
[23:13] <Laurenceb> yeah sure
[23:14] <fergusnoble> also the ELF binary format has a lot of tricks up its sleeve
[23:14] <fergusnoble> like relocatable binaries which will run anywhere in memory
[23:14] <Laurenceb> neat
[23:14] <fergusnoble> which is maybe what it does when you dont have a proper mmu
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[23:15] <Laurenceb> yeah I've played about with avr32 but that has a proper mmu
[23:15] <Laurenceb> you can just stick an elf on the sd card and run it
[23:16] <fergusnoble> thats cool
[23:17] <Laurenceb> it was interesting installing linux on the board - there a 4MB spi flash IC that it automatically boots from
[23:18] <Laurenceb> so theres two partitions on there, one with a uboot binary at 0 then a ext3 filesystem
[23:18] <Laurenceb> with gzipped kernel
[23:19] <Laurenceb> its a can of seting the right gpio pin to force spi flash boot, then uboot fires up and loads linux
[23:19] <Laurenceb> *case
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