I'm a windows user for context so I can't comment on what to use in linux
but if you are looping back it sounds ok
only if you have local echo you will get 2x show up. The outgoing & the returning data
yes better not to connect +3v just gnd tx & rx for most usb adapters
if you just get routers tx & your rx & gnd then you should see the data just after power on
you need the other rx-tx connecting to interact tho
I just use putty for serial data
Check the voltages on the Rx and tx pins on the router, see if there’s anything there at all.
If not, follow the traces back and see what’s missing. Some vendors kill the uart with resistors or jumpers.
I tried putty and also only have my inputs show up 1:1 (e.g. HELLO, not HHEELLLLOO) with the same USB serial adapter when I bridge the RX and TX pins. Is this expected behaviour?
Throughout the bootup process the voltage between the TX and GND pins of the router is 0V (+/-0.003V). There is no continuity between these pins (no beep in continuity mode, resistance too high for my meter to measure).
The only other devices I have that could read are Arduino Nano clones, but I don't have a sketch for that handy.
Thank you
Edit: I've decrypted and extracted the stock firmware for a DIR-1935 and DIR-882 A1. I'm poking around to see if I can figure out the flash layout there. Any pointers?
Still no luck on serial but fortunately, the exploit detailed here is unpatched on the firmware version on my DIR-1935, and the python3 script worked for me. I now have access via telnet.
The flash layout appears to match the DIR-882 A1 OEM layout. I base this on the output of cat /proc/mtd, where the "name" of each partition matches, and the "size" matches when you convert the size values in /proc/mtd to decimal then convert to kB.
I copied each of the mtd partitions (/dev/mtdX, X=0..6) with dd onto a usb stick. Are their contents of interest?
What's next?
Thank you
I believe with putty you will only see what's being receive "no local echo" off the top of my head
you do really want the flash backup and it be correct
the factory calibration data is custom to your device you want to back this up just in case
also it the easiest way to get decrypted firmware that will upload via the recover interface
but really you still need serial access to debug the loading process
would be good to test with the initramfs to find out what works & not
but you can with more risk just flash to the device
anyway you could try the dir-882 firmware it depend on if it requires the header
some do some don't
but then duplicate the DIR-882-A1 in openwrt with new correct model number
and by changing the model number will generate the header with the new model number
that I think will be required for flashing
and from then it just checking & finding what need changing
are there 2x MT7615Nx4 radios or do you have a DCDB setup where it's split x2 for 2.4G & 2x for 5G ?
How do I back up the flash and verify that the backup is correct? I'll do another dd backup of /dev/mtd0..6 on a different USB stick and compare the results to the first.
I'm out of ideas with the serial connection, I don't think I can get it going:
- Based on a video doing the same test, putty with default settings gives you 1:1 when you do a loopback test. This indicates that my USB adapter works.
- When I measure TX - GND voltage on the USB adapter, I get ~3.3V and it drops when I transmit. When I do the same on the router's TX - GND, I get ~0V.
- I don't see any unpopulated pads or anything on the PCB like on some TP-Link boards. The TX trace seems to go straight into the SOC's EMI shield and none of the caps on the other side have continuity to the TX pin.
How do I check the radios?
To ensure the header thing isn't an issue, should I build a new OpenWRT image (using the DIR-882 A1 as a starting point)? Could you link me to directions on how to do that?
How do you suggest I flash it? As far as I can tell I can flash OpenWRT with:
- D-Link Recovery GUI
- mtd_write -r -w write /tmp/firmware.img Kernel #(where /tmp/firmware.img is the firmware image)
Thanks again, I appreciate your patience
as I don't use the method you used to backup the mtd's "do get all of them"
you should be able to look at the firmware one in a hex editor & see the same type of header
that the Openwrt factory image has
while here look for the model number in the header and see it's it matches the real one
you do get a lot of information from the boot logs radios would be one of the things to look for
tho it's labelled as AC1900 so I'm thinking the same as the DIR-878's tho it's really ac2300
you can check your voltage range input of your serial but it seems like v3.3 but if it's only 5v it may not see the data at a lower level
anyway find your self a 10K resister & pull up the serial adapters RX worth a try & 10K won't break anything
you can look at the factory partition the 1st few bytes are the radio's model eg 15,76 for 7615 at 0 & 8000 HEX
as for flashing I would try the current DIR-882-A1 V23 factory image it has luci in it
you will find out quickly if it requires the correct model number in the header or not
tho this would be backed up by watching the serial port & looking for errors as it tries
found this old thread as well
here is the DIR-882-A1 factory file with the header manually changed to 1935
http://luckys.onmypc.net/openwrt/DIR-1935/openwrt-22.03.2-ramips-mt7621-dlink_dir-882-a1-squashfs-factory.bin
My dump of mtd5 has "DIR-1935" in the first 80 characters, and when viewed in a hex editor the model starts at the same place as the latest openwrt factory image for the DIR-882.
I tried a 9k pullup resistor and the TX pin on the router does pull up to ~3.3V, but it doesn't vary and I don't get any data in putty. I removed the USB adapter and changed the jumper to 5V mode and the TX-GND voltage went from ~3.3V to ~5V, so I think the jumper was set correctly in 3.3V mode.
My dump of mtd3 has 15,76,a0 at address 0 and 8000.
I couldn't access your link, but I tried flashing the DIR-882 A1's factory image (same filename as yours) after changing the DIR-882 to DIR-1935 and the D-link recovery gui rejected it (Update failed!). However, the unmodified DIR-882 worked and now it's running openwrt.
Both 2.4Ghz and 5Ghz networks work (used different SSIDs to confirm), however the range on the 5GHz one is really bad (about 50ft, up a staircase). At a location immediately before it drops, ping is still <10 ms and iperf3 speed is >150 Mbit/s on my laptop (intel dual-band wifi card). Any suggestions to improve range? I will try another power adapter for the router (the one I have for it is sketch), different channels, and different antenna orientations.
Now that it's running openwrt more or less correctly, what can I do to improve the state of documentation and build availability for the DIR-1935?
ok sounds like the recovery interface is not requiring the matching model number 
I think there was something about then not putting the MAC addresses in the radio calibration data
& it was showing bad mac addresses not sure it changes anything radio tho
but it did need fixing for later DIR-878's
but really entry's need to be made for the DIR-1935 same as for the DIR-878/882 etc
and a pull request genarated
not sure much can change for the radio's
I can't imagine the radio config have been swapped compared to the other ones
ether there is something wrong with you adapter or you have broken you serial interface
as in the other thread someone was able to use it find on the same model
other then changing channels I'm not sure what you can do for the radio's
just getting away from other interfering devices
not sure if you know how to build it your self but can start at the link below
I tried troubleshooting the wireless range again and after leaving the DIR-1935 running with the channel on auto for awhile the 5GHz band range improved and throughput was good. My guess is that the issue was interference with my nearby wifi AP. I haven't done thorough testing but will start using it instead of my regular AP for awhile and see if it behaves. Edit: Both the DIR-1935 and my regular AP are on the same 5GHz channel. Could just be interference and not a radio issue.
I reviewed the PR that added support for the D-Link DIR-867 A1 and DIR-882 A1. I added equivalent files/sections for the DIR-1935 A1 based on this PR. Following the high-level directions here, I made squashfs files for the DIR-882 A1 and DIR-1935 A1.
The checksums of the DIR-882 A1 squashfs-factory and squashfs-sysupgrade bin files do not match the latest equivalents linked here. Does that indicate a problem? If not, what's the next step? If it's firmware flashing, is it safer to use the D-Link Recovery GUI to flash the squashfs-factory file, or using LuCi to flash the squashfs-sysupgrade file? I never got serial access working so I don't want to brick a seemingly working device.
Thank you
Hi kewiha
even the change in the model number will change checksums
you should have a copy of the factory firmware
you should prune some of the blank ff's off the end tho
if you look in with a hex editor you will see where
I usually round it off & cut it XX000 address
after this you will be able to recover back to that version via the
recovery console
this is also the same place I recommend you flash the factory openwrt file
so in the end was there any changes from the DIR-882-A1 ?
are the leds still green ?
are the WIFI MAC address correct ?
The only difference I noticed from the DIR-882 A1 were related to LEDs. DIR-882 A1 has two USB activity LEDs that are not present on the DIR-1935 (visually identical to this picture of the DIR-867 A1). How I addressed this is below:
- For the dts file I started with target/linux/ramips/dts/mt7621_dlink_dir-882-a1.dts but removed the &leds section, consistent with target/linux/ramips/dts/mt7621_dlink_dir-867-a1.dts
- In target/linux/ramips/image/mt7621.mk I removed "kmod-usb-ledtrig-usbport" in DEVICE_PACKAGES
I'll try flashing the squashfs-factory file I made using the D-Link Recovery GUI. The squashfs-factory file I made does not appear to need the FF's at the end of the file trimmed, just like the squashfs-factory file for the DIR-882 A1 from the openwrt website. Hopefully this will work as expected and I won't have to try to reflash the OEM firmware to recover. I'll report back on the LEDs and MAC address afterwards.
it's the old factory firmware "D-Link OEM" that needs the extra padding removed
the kernel partition you saved
you need this to go back to D-Links OEM firmware
the picture shows the LED's as green are they still green ?
green is what's listed in the 8xx include file
if you can just use that it saves a lot of work
it seems weird that there is no usb led tho oh well
I built and flashed a build of v22.03.2 for the DIR-1935 A1 via DLink recovery gui and at first glance it seems to be behaving the same as when it had the DIR-882 A1 file on it.
LEDs are still green and behave as expected.
MAC addresses seem unchanged from the DIR-882 A1 firmware, and a MAC address lookup tool say they correspond to D-Link.
What testing should I do to confirm that everything is working properly?
all seems good
the green led labels match the firmware
check the the wan led works by default this will check you got the "01_leds" file correct
mac addresses should match the oem firmware
now it just to finish off the pull request
you may git it into the v23
I imagine the dts and image entry is the same as the dir-878-a1
I confirm that the WAN LED flashes when there is activity on the WAN port.
Created a PR: https://github.com/openwrt/openwrt/pull/11696
What's the process for adding the DIR-1935 to the TOH? Does that come after the PR is accepted?
Looks good as I would have imagined
I think the TOH will be add automatic same as the DIR-1960-A1
but people need to make the support page if wanted.
eg DIR-1960-A1 vs DIR-882-A1
some of the newer 878/882's don't have the correct MAC address
included in the radio data I think they are the same as the DIR-1960
and need to be offset form the lan mac
but your device seems not to need this
your device like the DIR-878 may also be a 4x4 radio so AC2600 not the listed AC1900
the 867 tho have parts removed
this will tell you
iw phy1 info
Available Antennas: TX 0xf RX 0xf
Configured Antennas: TX 0xf RX 0xf
You need to have a wiki account and then create a dataentry.