next »

[sloe]

i'm thinking we should look for a spare gpio, and create a new domain.  i think sharing the USB domain would be the next most preferable, depending on how often it already gets turned off/on.

paul

OK, I did some closer looking at one of the pics I got.  That SW11 pad seems to be controlled by pin 30 of the EC.  I wonder what voltage is sitting on it - all I'd have to do is add a component to that pad and we (theoretically) could have switched power controlled by the EC.

hmmmm.....I'm starting to think I need to "borrow" an o-scope from work and take it home.  This could be fun

[sloe]

Sloe & pgf,

I love what y'al are doing - GPS on the XO, and I'd love to have this whole idea highlighted on OLPC News through a Guest Post from y'all.  Please look for PM's from em ont he details.

Well, paul kinda needs an XO before he can do anything useful  , but I think this can be a fun collaborative project.

[pgf]

OK, I did some closer looking at one of the pics I got.  That SW11 pad seems to be controlled by pin 30 of the EC.

from a s/w point of view, a gpio hooked up to anything _but_ the EC would be preferable.  the code running in the EC a) isn't open, and b) is probably risky to update, if it can be done at all without jtag.  actually, it probably can be, but the lack of code makes it a non-starter.  maybe there's an unused i/o on one of the other small controllers -- SD, USB, etc.

[sloe]

I didn't think of that.  From this wiki entry, it appears that pins 31 and 32 would be the ones to use from the EC.  I'll see if I can't dig up something on the CaFe chip.

Looking at the tinderbox pdf you linked, it doesn't appear that we can piggyback on the SD or USB at all since they are controlled by the EC and southbridge.  Let me see what the options are on the CaFe.


edit:
ok, looks like all the GPIOs are used up on the CaFe.



taken from this data sheet.

[pgf]

i guess i was thinking of seeing whether either the USB or SD controller had an unused gpio we could get at.  (but maybe you understood that already.)  for instance -- could we repurpose the SD write-protect line?  it depends on who controls it and where.

does the geode itself have any gpio?  unfortunately, if they're unused, they're probabaly also inaccessible.

ironically, i notice there's a gpio on the GS405 you pointed out earlier.  guess that's not helpful, eh?  :-)

(i was looking because i was curious as to whether any of the gps modules had power-down inputs.)

paul

[pgf]

i had another thought on the way home.  you're thinking of a FET, or something similar (i don't actually know how much current a FET can handle) to control the power, i assume?  what if we added an 8-bit/8-pin micro to the solution -- something like one of the ATtiny series from Atmel (or a PIC, but i have a programmer for the AVR parts).  the micro could monitor the serial lines, and keep power applied to the GPS (via the FET, or whatever it is) as long as there were periodic transitions on the TX data line.  i have to believe that there's some sort of null command (even just a "break" character) that could be sent to the GPS every 30 seconds or so to keep it alive.  effectively we'd be reusing the TX line as the "spare gpio" we were looking for.

of course, if there were a tiny micro that had the ability to switch that much current, then that would be a win in terms of ease of hookup, turning it into just one component.
paul

[sloe]

I did some more research last night and think I've figured out what the SW11 pad is for.  According to this pic over at the wiki, there is a pushbutton switch mounted there.  I'm assuming those pics are from one of the pre-release systems, and with it connected to pin 30, that is a hard switch to reset the EC.  It won't give us switched power.

Now, as for the Atmel stuff you mentioned,  I'm looking at it.  The one thing I am having trouble finding is the instruction sets for the GPS chips.  I found the Open Source GPS Project, but it didn't tell me what I was looking for.  Heck, I'm not sure what I'm looking for which is probably why I can't find it.  It's been a while since I've done component level design - like 15 years    The cobwebs are pretty thick up there in the noggin, but I'm workin' on it.

sloe, how hard is it to get in the handle area? I think in the strap holes or handle would be a perfect spot for the GPS antenna. And if you could find a white one.....

I actually thought of that.  I need to measure the hole and see if the one miniature antenna I've located would fit there.  Getting a white housing for it shouldn't be that hard, but I've been wrong before.  Although, the helical antennas can be mounted inside the handle, no problem.  They're not that big.

[mattd]

i'm supposed to hear about "attention to detail" from somone that can't get my initials right?  :-)

How embarassing. I was going to say paul, but we just met. Maybe after the hardware mod.

what if we added an 8-bit/8-pin micro to the solution -- something like one of the ATtiny series from Atmel (or a PIC, but i have a programmer for the AVR parts).

YES! I've been waiting for (or trying to think of) a reason to buy Peatman's QuikFlash board for a year or two.

We could essentially monitor anything that would change states during a 'suspend'. Not to mention we could do some brainstorming and find other uses for the micro.

I haven't been this excited since Christmas. Now I need to actually start looking at all that documentation sloe has be posting links to.

[pgf]

Now, as for the Atmel stuff you mentioned,  I'm looking at it.  The one thing I am having trouble finding is the instruction sets for the GPS chips.

they're all the same.  they spit out  a variety of lines of text, known as the NMEA protocol.  i forget what it stands for -- i think the M is for "marine", because the standard began as a way for stuff in the cockpit of boats to talk to one another.  it's all just 4800 baud serial.

[sloe]

Yeah, its the NMEA, National Marine Electronics Association.  The specific output code protocol the GPS chips talk on is the NMEA 0183 ASCII Specification.  They want $270 to explain it to you.

What I'm trying to figure out is whether this is the input protocol to the chips, also, since it is defined as a broadcast language.  Specifically, what I'm hoping to find is the capability on one of these GPS modules to place it in standby (warm) or off (cold) mode (and bring it back) via an instruction from the serial bus.  If I find it, then the extra component will not be needed.

Now, as for the extra component - is it possible to drive the TX line high, and leave it high, on an RS232 or LVTTL bus?  Using this would prevent any instructions to the GPS like current position and almanac data, so I'm not sure I want to go that route.  The direction you were going with it, to jsut monitor the line, might be a better idea, but I haven't located a single component that will switch that much power as well as handle instructions.  We may have to use an instruction chip (the ATtiny) and a FET relay of some sort to manage power.  I'm still looking, though...

[strollin]

Very interesting discussion but I personally don't see what purpose is served by mounting the GPSr in the XO?

What is the intended application of the GPS enabled XO?  It's too large and bulky to be used as a handheld GPS while hiking so the only application I see for it is for auto navigation.  If you mount the receiver in the XO, won't that mean the XO will need to ride on the dash in an auto?  Many autos don't have enough room on the dash for an XO.

Seems to me instead of spinning wheels trying to come up with a hardware solution, it would make more sense to spend a few $$ (about $42 on Ebay, including shipping) to get a USB hockeypuck GPSr, plug it into one of the available USB ports and be done with it.  Only the GPSr needs to be on the dash or on the windshield, the XO can ride elsewhere.  All we need then is software for the XO that can take advantage of the GPSr. 

[pgf]

What I'm trying to figure out is whether this is the input protocol to the chips, also, since it is defined as a broadcast language.  Specifically, what I'm hoping to find is the capability on one of these GPS modules to place it in standby (warm) or off (cold) mode (and bring it back) via an instruction from the serial bus.  If I find it, then the extra component will not be needed.

good point.  that would have to be in the module-specific docs -- it's certainly outside the bounds of normal GPS operation.

Now, as for the extra component - is it possible to drive the TX line high, and leave it high, on an RS232 or LVTTL bus?  Using this would prevent any instructions to the GPS like current position and almanac data, so I'm not sure I want to go that route.

i'm not sure i'm following you in any case.  almost all data from a GPS module flows out of the module. there are possibly some control commands going the other way, but in general, unless it's a sophisticated device that can do track logging, there's not much reason to send it commands.  it just talks to you when it has something to say (about once a second).

The direction you were going with it, to jsut monitor the line, might be a better idea, but I haven't located a single component that will switch that much power as well as handle instructions.  We may have to use an instruction chip (the ATtiny) and a FET relay of some sort to manage power.  I'm still looking, though...

displaying my ignorance here -- can several gpio ports be wired in parallel to drive the module?  the AVR i/o ports can supply 30mA.  4 of them together would power a module.  is that a totally unreasonable idea?

[pgf]

Very interesting discussion but I personally don't see what purpose is served by mounting the GPSr in the XO?

very good question.  :-)

i'm not sure what sloe's motivation is, but mine is this:  i've been using a similar linux-based handheld device on the tankbag of my motorcycle for years while touring.  the thing that really attracted me to the XO laptop is the display -- mine, even with its 20 watts of backlight, is unreadable in direct sunlight.  while i could certainly get a small USB gps device, it's a little awkward, especially with having to keep the wireless antenna up to give access to the port.  it's really just a matter of convenience, for me, to have it built-in.  and a good project, besides.

paul

[sloe]

Very interesting discussion but I personally don't see what purpose is served by mounting the GPSr in the XO?

Two tongue-in-cheek answers immediately come to mind:
     1.  Why not?
     2.  Because I can.

I'm looking at this as a project to teach myself a few things.  I would probably get more benefit out of adding a Bluetooth interface to the XO, but I want to play with GPS, so that's where I'm going.  My finance committee (the missus) might put a damper on any experimentation, and the usage committee (the 3 year old owner of our XO) might get upset if I break it, so I don't know how far I can take this beyond the theoretical stage.  I'll probably end up using this experience to add GPS to a very old laptop sitting in my cabinet and make it my new automotive navigation/entertainment device.

I agree that buying a hockey-puck receiver and plugging it in is the easiest route, but I don't like taking the easy way out of things.  I'm having fun - aren't I allowed to?

[mattd]

Very interesting discussion but I personally don't see what purpose is served by mounting the GPSr in the XO?

It gives me an outlet for my dorkdom. And like sloe said, for other applications. Lots of other applications if we go with the microcontroller. Say and LCD below the screen to give detailed battery info, storage info, RAM usage info, CPU monitor, etc. Or moving LEDs behind the big XO logo. Or more inputs for the measure activity.

displaying my ignorance here -- can several gpio ports be wired in parallel to drive the module?  the AVR i/o ports can supply 30mA.  4 of them together would power a module.  is that a totally unreasonable idea?

I think it's possible. I looked up the specs for a PIC18FXX2 and it does 25mA per I/O pin and 200mA per bank so it's another option. It also has a UART so we could use the internal serial bus to control it (we do have s/w access to it don't we?).