Fail to boot when booting with TTL connected.

[yaleh]

With Mecury m301 (a TL-MR3040 clone) and TL-WR740N, if TTL is connected before plugging the power, it fails to boot. There's no light, network is not up either (failed to ping 192.168.1.1). But if I power it up and then plug the TTL line, it will be OK.

I'm using a prebuilt version following the link at openwrt.org ( http://wiki.openwrt.org/toh/tp-link/tl-wr740n#u-boot.mod.for.tp-link.with.ar9331 ). Will it help if I check out the latest code and compile it?

[pepe2k]

Hello yaleh,

I don't think that this issue is related with software.
What adapter are you using and how did you connect it?

Regards

[yaleh]

A USB-TTL adapter. Actually, I tested it with the original bootloader and it works fine.

[pepe2k]

Hello yaleh,

What USB-TTL adapter, exactly?

I'm using MR3040 with my modification (first release: https://github.com/pepe2k/u-boot_mod/releases/tag/2013-08-19) and I don't have any problems with my USB-UART adapter, based on CP2102.

Regards

[yaleh]

The USB-TTL is PL-2303MX based, cheap and popular at taobao.com .

Actually, I just compiled u-boot_mod with OpenWRT Toolchain, and the issue still exists. Is it related to the version of WR740N? I'm testing with v5.2 now. When I plug the power, wait for the lights, and then plug TTL cables, it's OK. Does the code check TTL or pins and hang up on booting?

[pepe2k]

Hello yaleh,

As far I know, there isn't any checking the UART pins level. If you connect adapter and power on the device (with my modification), the power LED is active?

Regards

[yaleh]

Without TTL connected, all LEDs except the LOCK shine for about 1s and then turn off. Then I can connect the TTL and it works.

With TTL connected, only the LAN1 shows weak light (I believe it's shinning). No output at TTL.

[pepe2k]

Hello yaleh,

I don't have any idea what may be wrong. I suspect that probably your router version has different GPIOs configuration.

Regards