I was really wondering how much memory does a few lines of command take up? I just ordered some 144 kb tags because I can't use mifare classic cause I have a nexus 4. I was just wondering if that would be enough for a few toggles.
cfmusicman said:
I was really wondering how much memory does a few lines of command take up? I just ordered some 144 kb tags because I can't use mifare classic cause I have a nexus 4. I was just wondering if that would be enough for a few toggles.
Click to expand...
Click to collapse
144Kb tags!?? Are you going to store a whole library in it?
Assuming you ordered some 144 Bytes tags, the memory you need is just a few bytes more than the commands you are actually writing on it.
Also, some bytes are used internally, based on the tag technology.
Example (using MiFare UltraLight, which has only 64 bytes):
NDEF Command: Open site "http://www.google.com/"
--> 16 Bytes were used for MiFare UltraLight (UID, Access Conditions, etc.)
--> 8 Bytes were used for NDEF structure
--> 22 Bytes were used for your data (the link itself).
TOTAL: 46 Bytes used.
I'm using some apps on my Galaxy Nexus phone, that are really useful:
- NFC TagInfo --> Useful to show the raw data and some more technical information;
- Tagstand Writer --> Easiest app I found to write NDEF tags;
Hope I could help you.
cfmusicman said:
I was really wondering how much memory does a few lines of command take up? I just ordered some 144 kb tags because I can't use mifare classic cause I have a nexus 4. I was just wondering if that would be enough for a few toggles.
Click to expand...
Click to collapse
I think you mean 144byte tags right?
As for how much memory a few commands take up, I've attached a couple of images that should help you. These toggles were programmed onto 144byte NTAG203 tags.
Related
Hi,
I'd like to create a App which I want to unlock with a NFC based smart card like a Mifare SmartMX or DESfire. So the user needs the card to do certain stuff within the application.
After the smart card is programmed with "java card" for example, is it possible to communicate with android? Is android even possible to deal with the cryptosystems?
Has anybody tried that before or knows something about it?
Thanks very much for ur help..
At the moment I'm using a galaxy nexus with android 4.0.4
cheers
-eiMer
I know NFC TagInfo ( play.google.com/store/apps/details?id=at.mroland.android.apps.nfctaginfo&hl=en ) is able to communicate with Desfire card (among with a lot of other kinds).
It can even read the secured data if it is given the correct keys.
The android SDK provides classes to handle Mifare Classic card but not Desfire AFAIK. I don't know if the used an external Desfire library or if they implemented the whole protocol by themselves (it seems to be a very big research group - founded by NXP - so they might have) but it is definitely possible to use Desfire cards with Android.
Thanks for your help.
Ill try to find out how they managed the communication.
If I get some results Ill post them here.
eiMer said:
After the smart card is programmed with "java card" for example, is it possible to communicate with android?
Click to expand...
Click to collapse
Smartcards and also DESFire communicate using the ISO14443-4 transmission protocol (also known as ISO-DEP). Android provides the class IsoDep to communicate with these cards. Depending on the card, you would then exchange either ISO7816-4 APDU commands (e.g. with your JavaCard applet or with the DESFire card in ISO 7816-4 framing mode) or proprietary commands (e.g. with DESFire native command set).
eiMer said:
Is android even possible to deal with the cryptosystems?
Click to expand...
Click to collapse
The Android API already provides support for a wide range of cipher suites, hash functions ... If that's not sufficient for your type of card, you could also implement your own algorithms.
Gildas35 said:
I know NFC TagInfo is able to communicate with Desfire card (among with a lot of other kinds).
Click to expand...
Click to collapse
Correct. I've implemented support for DESFire. For the moment, however, only authentication with the default key (DES, all zeros) is supported.
Gildas35 said:
The android SDK provides classes to handle Mifare Classic card but not Desfire AFAIK. I don't know if the used an external Desfire library or if they implemented the whole protocol by themselves (it seems to be a very big research group - founded by NXP - so they might have) but it is definitely possible to use Desfire cards with Android.
Click to expand...
Click to collapse
I've implemented the protocol myself (on top of the IsoDep class). The original DESFire protocol is pretty straight forward and there's lots of help on the web. When it comes to the EV1 extensions (improved cryptography) things get a bit more difficult.
br
Michael
I realize there's a ton of different sites that sell NFC stickers and they all have various storage sizes ranging from 512 bytes to 2 Kb. So what's the general rule of thumb when it comes to actions vs storage space?
Obviously the higher the storage space, the more that can be automated with 1 tag. But say you just want to toggle a few system settings (volume, Bluetooth, brightness) and open one or two apps. Would a 512 byte tag suffice?
Maybe someone with more knowledge on the subject should create a guide generalizing this sort of stuff (broadly of course). I know it would certainly help me and any others wondering the same thing.
squiddy20 said:
I realize there's a ton of different sites that sell NFC stickers and they all have various storage sizes ranging from 512 bytes to 2 Kb. So what's the general rule of thumb when it comes to actions vs storage space?
Obviously the higher the storage space, the more that can be automated with 1 tag. But say you just want to toggle a few system settings (volume, Bluetooth, brightness) and open one or two apps. Would a 512 K tag suffice?
Maybe someone with more knowledge on the subject should create a guide generalizing this sort of stuff (broadly of course). I know it would certainly help me and any others wondering the same thing.
Click to expand...
Click to collapse
512k is a lot of space (where are 512k tags?).
Generally speaking 144 bytes (Ultralight C, NTAG203) is quite a bit and suitable for most applications.
If you need more space Classic 1K tags work (but these technically aren't NFC forum tags). 2K and 4K tags are generally overkill but are available.
If you are planning on using NFCTL most actions take 4-5 bytes (with the header being about 25 bytes). Actions that must store text (launching an App or URL for example) will store more space as they must store the string on the tag (generally 1 byte per string character plus 2 bytes instruction set).
Oh, oops. Meant to put 512 bytes. Correcting OP. Thanks for catching that.
Ok. So what about making a tag a toggle? Since (I imagine) you have to have a command for on and a command for off, does using it that way essentially double the space used?
squiddy20 said:
Oh, oops. Meant to put 512 bytes. Correcting OP. Thanks for catching that.
Ok. So what about making a tag a toggle? Since (I imagine) you have to have a command for on and a command for off, does using it that way essentially double the space used?
Click to expand...
Click to collapse
Unsure exactly what you're referencing. For a single Toggle command in a Task tag it takes no more space than enable,disable - the command merely indicates toggle instead of enable or disable. If you're referencing a switch tag then it writes essentially two Task tags to the physical tag (so that requires more space).
krohnjw said:
Unsure exactly what you're referencing. For a single Toggle command in a Task tag it takes no more space than enable,disable - the command merely indicates toggle instead of enable or disable. If you're referencing a switch tag then it writes essentially two Task tags to the physical tag (so that requires more space).
Click to expand...
Click to collapse
Haha my bad. I'm a total noob with this stuff (obviously) as I only got my Galaxy Nexus 2 weeks ago and only just started looking into this stuff. What I mean is 1 tag that when tapped once, turns volume up, screen brightness up, and opens an application, and a second tap will essentially revert the settings and maybe close the aforementioned app. Correct me if I'm wrong, but from the sound of my own description, it sounds like a combination of a toggle command (tap1: volume up, tap2: volume down) and a switch tag (opening and closing an app).
alicechong89 said:
512 bytes should be plenty.
On NFC Task Launcher, if I set these actions: enable wifi, set alarm, launch calculator, and set ringer volume, the total required is about 65 bytes.
Click to expand...
Click to collapse
Thanks for that bit of info, that clarifies things quite simply as I imagine that's pretty much all I'll be using the tech for.
curious why you wouldn't just make a profile using tasker to do the command combinations, then program the smallest tag to execute that one profile/script/macro ?
/first post!
danfinger said:
curious why you wouldn't just make a profile using tasker to do the command combinations, then program the tag to execute that one profile/script/macro ?
/first post!
Click to expand...
Click to collapse
Don't have Tasker and I'm not sure if I want to delve into its complexities, even though it would probably be easier (in some ways) to go that route.
Congrats on your first post, btw!
Hi,
I'm looking for a way to read & write on a Mifare Ultralight. I know a couple of applications available on the Play Store allow the possibility to read them, but I didn't find any application allowing me to write back (for example, change the data and save it back).
Is there a way to do so?
Also, is it possible to plug in the Android to my computer to use the NFC capabilities and to code in another language than Java? (some kind of bridge)
Thanks a lot for your support!
jpmonette said:
Hi,
I'm looking for a way to read & write on a Mifare Ultralight. I know a couple of applications available on the Play Store allow the possibility to read them, but I didn't find any application allowing me to write back (for example, change the data and save it back).
Is there a way to do so?
Also, is it possible to plug in the Android to my computer to use the NFC capabilities and to code in another language than Java? (some kind of bridge)
Thanks a lot for your support!
Click to expand...
Click to collapse
Have you tried NXP NFC Writer app? As of now there is no way to use your phone as a USB NFC reader.
Well I have both TagWriter and TagInfo. I can read the content of my NFC chip with TagInfo, but I can't with TagWriter. That's why I'm looking for something else to do the job, but can't find much on the Play Store.
jpmonette said:
Well I have both TagWriter and TagInfo. I can read the content of my NFC chip with TagInfo, but I can't with TagWriter. That's why I'm looking for something else to do the job, but can't find much on the Play Store.
Click to expand...
Click to collapse
Is the tag write locked? Formatting Classic 1K tags to NDEF is part of the standard NFC/NDEF libraries on Android. This allows full write access.
If you're trying to do it without NDEF then you have a different set of issues you'll need to deal with.
Nfc task launcher
Sent from my Nocturnal HOX
krohnjw said:
Is the tag write locked? Formatting Classic 1K tags to NDEF is part of the standard NFC/NDEF libraries on Android. This allows full write access.
If you're trying to do it without NDEF then you have a different set of issues you'll need to deal with.
Click to expand...
Click to collapse
Well, some pages are writable, some others aren't. Still, I can't get it to work with any apps I found (also the one people suggested in here).
i have a galaxy s3, and today i got an infineon myd nfc (SLE 66R32P), but i can't store anything on it. i tried to use the programs nfc retag, nfc task launcher and the nxp tag writer, but none work. i've attached some screenshots.
(the text on the first says: "tag not supported. it's no NDEF-tag or NDEF-formatable tag.)
i know that it is not write-protected. the documentation of the tag says:
documentation
NFC Tag Operation
• Support of NFC Forum™ - Type 2 Tag Operation Specification
• Up to 2048 bytes NFC memory available
– organized in static or dynamic memory structure
– pre-defined memory size for NFC Forum™ Type 2 Tag Operation (up to two 1 kByte sectors)
• Pre-configured NFC memory with empty NDEF message (INITIALIZED state)
Click to expand...
Click to collapse
wergor said:
i have a galaxy s3, and today i got an infineon myd nfc (SLE 66R32P), but i can't store anything on it. i tried to use the programs nfc retag, nfc task launcher and the nxp tag writer, but none work. i've attached some screenshots.
(the text on the first says: "tag not supported. it's no NDEF-tag or NDEF-formatable tag.)
i know that it is not write-protected. the documentation of the tag says:
Click to expand...
Click to collapse
Ok, can only speak for NFC ReTag
the tag specification says : "Pre-configured NFC memory with empty NDEF message (INITIALIZED state)" ---> so it should be already NDEF pre-formated and the NFC ReTag error message "already NDEF-formated" should be correct .... Have you tried to write a special NFC ReTag tag ?
btw. you can pm me in german for further support , if you want ....
ascsa said:
Ok, can only speak for NFC ReTag
the tag specification says : "Pre-configured NFC memory with empty NDEF message (INITIALIZED state)" ---> so it should be already pre-formated and the NFC ReTag error message "already NDEF-formated" should be correct .... Have you tried to write a special NFC ReTag tag ?
btw. you can pm me in german for further support , if you want ....
Click to expand...
Click to collapse
i tried that too, it says "Tag is write protected, blocked or not formated! nothing done! you can try to format the tag if the error persists!"
wergor said:
i tried that too, it says "Tag is write protected, blocked or not formated! nothing done! you can try to format the tag if the error persists!"
Click to expand...
Click to collapse
Hmmm Ok,
unfortunately this is the NFC ReTag message, if the app could not write your tag .... Normally it occurs when the tag is not NDEF formated or you write-protected the tag ... I assume this is a new tag, and you never write-protected it .... ?
Strange, according to the tag specs this tag should work ... unless i missed something obviously ....
EDIT: had a look at the tag documentation, found this on page 7:
Infineon's my-d™ NFC family convinces with fast communication speed and high robustness. Furthermore, the
SLE 66RxxP family can be operated as NFC Forum™ Type 2 Tag.
and this on page 11:
The my-d™ NFC are delivered with pre-configured NFC memory; the Capability Container bytes are programmed
and the data area holds an empty NDEF message; this represents the NFC Forum™ Type 2 Tag INITIALIZED
state within the tag life cycle. With this pre-configuration the my-d™ NFC can be immediately used in NFC
infrastructures.
For further details regarding the NFC initialization of my-d™ NFC please refer to the Data Book and the Application
Note “How to operate my-d™ devices in NFC Forum™ Type 2 Tag infrastructures” available at Chip Card &
Security " Attention: This pre-configuration can be over-written to any value. Initial shipments of the my-d™ NFC
devices have been delivered without this configuration."
So, perhaps you got one of these initial shipment tags .....
ascsa said:
Hmmm Ok,
unfortunately this is the NFC ReTag message, if the app could not write your tag .... Normally it occurs when the tag is not NDEF formated or you write-protected the tag ... I assume this is a new tag, and you never write-protected it .... ?
Strange, according to the tag specs this tag should work ... unless i missed something obviously ....
EDIT: had a look at the tag documentation, found this on page 7:
Infineon's my-d™ NFC family convinces with fast communication speed and high robustness. Furthermore, the
SLE 66RxxP family can be operated as NFC Forum™ Type 2 Tag.
and this on page 11:
The my-d™ NFC are delivered with pre-configured NFC memory; the Capability Container bytes are programmed
and the data area holds an empty NDEF message; this represents the NFC Forum™ Type 2 Tag INITIALIZED
state within the tag life cycle. With this pre-configuration the my-d™ NFC can be immediately used in NFC
infrastructures.
For further details regarding the NFC initialization of my-d™ NFC please refer to the Data Book and the Application
Note “How to operate my-d™ devices in NFC Forum™ Type 2 Tag infrastructures” available at Chip Card &
Security " Attention: This pre-configuration can be over-written to any value. Initial shipments of the my-d™ NFC
devices have been delivered without this configuration."
So, perhaps you got one of these initial shipment tags .....
Click to expand...
Click to collapse
Yes, i think it is one of those... guess i need a nfc reader for pc to initialize the tag...
wergor said:
Yes, i think it is one of those... guess i need a nfc reader for pc to initialize the tag...
Click to expand...
Click to collapse
yep, but I´m not sure if anybody other than the manufacturer can initialize these tags ...
Anyway ,you should be able to use this tag (without initializing) with NFC ReTag ... writing a special NFC ReTag tag is not possible, but you only need that for better dispatching process and everything else should work without writing something to the tag
ascsa said:
yep, but I´m not sure if anybody other than the manufacturer can initialize these tags ...
Anyway ,you should be able to use this tag (without initializing) with NFC ReTag ... writing a special NFC ReTag tag is not possible, but you only need that for better dispatching process and everything else should work without writing something to the tag
Click to expand...
Click to collapse
well, the tag IS initialized, but only with zeros (see screenshots) and not with a NDEF message.
documentation said:
The my-d™ NFC are delivered with pre-configured NFC memory; the Capability Container bytes are programmed
and the data area holds an empty NDEF message; this represents the NFC Forum™ Type 2 Tag INITIALIZED
state within the tag life cycle
Click to expand...
Click to collapse
as i understand it, "initializing" (what i want to do) just means writing any ndef message to the tag (and set those "capability container bytes").
if i had an nfc reader i could test this, i already found a program (for pc) can write NDEF messages to tags. but i somehow doubt that works. it's never that easy maybe android just doesn't support that particular tag...
I've been seeing posts on Google+ of people having trouble to use Android Beam and some tags. The antenna is under the X of Nexus on this device, which is different from the previous Nexus 7 (which was more towards the top). Still, I'm curious if more people have trouble with Beam/NFC tags.
haven't had any trouble yet. only sent a few pictures back and forth from my galaxy nexus, but everything has transferred just fine. haven't tried web pages, videos, or apps though.
Yeah, I've seen mentions of beam issues, too. No problems here, though.
Sent from my Galaxy Nexus
Worked normal using super beam( I recommend that over android beam anyways)
Sent from my Nexus 7 using Tapatalk 4 Beta
Fine for beam
Yeah, same here. No problems. I don't use NFC much, but tested it a little with my new N7 HD (or whatever we're calling it) and my SGS III and it they both made a sound (phone buzzed too) no problem. I'd just as soon use the QR part of super beam anyway since my good batteries (zero lemon!) don't have NFC.
It does not work with me I tried under X and every where but still wont work
I tested with Nexus 4, Galaxy s4, and Nexus 4 Wireless Charger
I tried it with my old Nexus 7, and I had to hold them together and wiggle them around for several seconds before it beeped. This is probably because I had no idea the antenna was down in the middle. I'll have to try the middle of the new one against the top of the old one and see if it is more immediate.
I returned my Nexus 7 due to the qi not working on it, prior to doing that though I had checked out the nfc with both a Razr Maxx HD and a DNA... worked fine. After exchanging the Nexus7 with a new one, my qi charge now works but the NFC doesn't. I table and/or phone makes a beep and the "Touch to send" screen pops up but no files or images send. Not too worried since I don't think it's an option I would use much and I don't want to exchange the tablet again for a different one (again).
I've had no problems sending or receiving. In addition wireless charging works great, too. It's the only way I charge the N7 since I got it.
This is what I have been able to determin.
Works:
- Device to device (Nexus 7 v2 & GAlaxy Note II)
- Generic NFC tags from ebay (They also work with my NOTE II and TecTiles app)
- NFC Task Launcher app
- UPDATE: Samsung TecTiles just worked after being written with NFC Task Launcher.
Does not work:
- UPDATE: Samsung TecTiles just worked after being written with NFC Task Launcher.
- Samsung TecTiles app
Don't have and have not tried with the new TecTiles 2
This may shed some light into the TecTiles issue:
http://www.anandtech.com/show/6919/...le-with-original-tectiles-tectile-2-announced
RojasTKD said:
This is what I have been able to determin.
Works:
- Device to device (Nexus 7 v2 & GAlaxy Note II)
- Generic NFC tags from ebay (They also work with my NOTE II and TecTiles app)
- NFC Task Launcher app
- UPDATE: Samsung TecTiles just worked after being written with NFC Task Launcher.
Does not work:
- UPDATE: Samsung TecTiles just worked after being written with NFC Task Launcher.
- Samsung TecTiles app
Don't have and have not tried with the new TecTiles 2
This may shed some light into the TecTiles issue:
http://www.anandtech.com/show/6919/...le-with-original-tectiles-tectile-2-announced
Click to expand...
Click to collapse
I can also confirm that Kamor NFC Tags are not working with the Nexus 7 (2013) Wifi or LTE models. Here is information from the NXP TagInfo app regarding the non-supported tags from a Nexus 7 (2012) where the tag tiles work.
* TagInfo scan (version 2.00) 2013-10-08 09:15:09 **
-- INFO ------------------------------
# IC manufacturer:
NXP Semiconductors
# IC type:
MIFARE Classic (MF1S50)
-- NDEF ------------------------------
# NFC data set storage not present:
Maximum NDEF storage size after format: 716 bytes
-- EXTRA ------------------------------
# Memory size:
1 kB
* 16 sectors, with 4 blocks per sector
* 64 blocks, with 16 bytes per block
-- TECH ------------------------------
# Technologies supported:
MIFARE Classic compatible
ISO/IEC 14443-3 (Type A) compatible
ISO/IEC 14443-2 (Type A) compatible
# Android technology information:
Tag description:
* TAG: Tech [android.nfc.tech.MifareClassic, android.nfc.tech.NfcA, android.nfc.tech.NdefFormatable]
android.nfc.tech.NdefFormatable
android.nfc.tech.MifareClassic
android.nfc.tech.NfcA
* Maximum transceive length: 253 bytes
* Default maximum transceive time-out: 618 ms
After some Googling, I have found that Android supports a few NFC tag technologies (and that some of them are RFID standards also).
Android supports the following NFC tag technologies:
TagTechnology - The interface that all tag technology classes must implement.
NfcA - Provides access to NFC-A (ISO 14443-3A) properties and I/O operations.
NfcB - Provides access to NFC-B (ISO 14443-3B) properties and I/O operations.
NfcF - Provides access to NFC-F (JIS 6319-4) properties and I/O operations.
NfcV - Provides access to NFC-V (ISO 15693) properties and I/O operations.
IsoDep - Provides access to ISO-DEP (ISO 14443-4) properties and I/O operations.
Ndef - Provides access to NDEF data and operations on NFC tags that have been formatted as NDEF.
NdefFormatable - Provides a format operations for tags that may be NDEF formattable.
Can anyone else who is having problems with specific NFC tags or tiles verify with TagInfo the type of tag used? I suspect there may be a problem with NfcA compatibility on the NFC stack used with the 2013 models.
buckofive said:
I can also confirm that Kamor NFC Tags are not working with the Nexus 7 (2013) Wifi or LTE models. Here is information from the NXP TagInfo app regarding the non-supported tags from a Nexus 7 (2012) where the tag tiles work.
* TagInfo scan (version 2.00) 2013-10-08 09:15:09 **
-- INFO ------------------------------
# IC manufacturer:
NXP Semiconductors
# IC type:
MIFARE Classic (MF1S50)
-- NDEF ------------------------------
# NFC data set storage not present:
Maximum NDEF storage size after format: 716 bytes
-- EXTRA ------------------------------
# Memory size:
1 kB
* 16 sectors, with 4 blocks per sector
* 64 blocks, with 16 bytes per block
-- TECH ------------------------------
# Technologies supported:
MIFARE Classic compatible
ISO/IEC 14443-3 (Type A) compatible
ISO/IEC 14443-2 (Type A) compatible
# Android technology information:
Tag description:
* TAG: Tech [android.nfc.tech.MifareClassic, android.nfc.tech.NfcA, android.nfc.tech.NdefFormatable]
android.nfc.tech.NdefFormatable
android.nfc.tech.MifareClassic
android.nfc.tech.NfcA
* Maximum transceive length: 253 bytes
* Default maximum transceive time-out: 618 ms
After some Googling, I have found that Android supports a few NFC tag technologies (and that some of them are RFID standards also).
Android supports the following NFC tag technologies:
TagTechnology - The interface that all tag technology classes must implement.
NfcA - Provides access to NFC-A (ISO 14443-3A) properties and I/O operations.
NfcB - Provides access to NFC-B (ISO 14443-3B) properties and I/O operations.
NfcF - Provides access to NFC-F (JIS 6319-4) properties and I/O operations.
NfcV - Provides access to NFC-V (ISO 15693) properties and I/O operations.
IsoDep - Provides access to ISO-DEP (ISO 14443-4) properties and I/O operations.
Ndef - Provides access to NDEF data and operations on NFC tags that have been formatted as NDEF.
NdefFormatable - Provides a format operations for tags that may be NDEF formattable.
Can anyone else who is having problems with specific NFC tags or tiles verify with TagInfo the type of tag used? I suspect there may be a problem with NfcA compatibility on the NFC stack used with the 2013 models.
Click to expand...
Click to collapse
The article I posted clearly states the issue. Here is an excerpt of the pertinent part:
" When I saw the presence of BCM2079x, I remembered that this reader doesn’t read MIFARE tags, which the NXP solution does, since it is an NXP tag format. Instead Broadcom only reads tags which adhere to the standard NFC Forum tag types. Ordinarily this isn’t much of a problem, as long as users are aware of the limitation and to stay away from MIFARE classic tags on an incompatible reader."
Sent from my Nexus 7 using Tapatalk 4
I can't my NFC to work at all. I have the ntag203 tags so I know their compliant. I get nothing at all. Guess I'm going to take this tablet back and exchange. I've used several apps. If any one knows a fix or how to check and see if the hardware is at fault please pm me If I knew how to check I would.
asdf1nit said:
I can't my NFC to work at all. I have the ntag203 tags so I know their compliant. I get nothing at all. Guess I'm going to take this tablet back and exchange. I've used several apps. If any one knows a fix or how to check and see if the hardware is at fault please pm me If I knew how to check I would.
Click to expand...
Click to collapse
neither do I, it can't find a nexus 4/nexus 5 nor compatible tags
If someone find a fix, post your solution please
it worked only ONCE with a tag, then I tried to read it again and since then nothing...I tried changing roms, full wipe
I found this:
http://www.andytags.com/nfc-tags-compatibility-issues.html
...not sure if it's helpful, but there you go.