odroid hc1: connection uart to uart external device pb

[r2d2r01]

Hi armbian staff and users, i must/try to connect through uart (HC1 /Dev/ttySAC2) to an external uart device.
1. As uart /dev/ttySAC2 is used by boot/kernel, /sbin/agetty has been renamed to stop its launching / lock rather than rebuild uboot/...
2. So as powers supply of 2 uart are differents, 2 converters UART/USB are installed on 2 sides
HC1 <-> UART/USB(CP2102N) <=======> USB/UART(XR21V14xy) <-> device. External PS 5v is connected on USB(vcc:gnd), red light on CP2102N is up.
I precise 2 points :
HC1 <-> UART/USB(CP2102N) <=======> laptop=OK
DEVICE <-> UART/USB(XR21V14xy) <=======> laptop=OK
Nothing TX/RX, where is the mistake ?
Any clue are welcome
Best regards
Frederic

ps: armbian buster 4.14

[r2d2r01]

Hi, i have verified all power supply etc...., the 5v is present at all stages but always no result, only when i connect to my laptop that runs fine.
The only conclusion is that HC1(kernel) has not ability to be usb host / initiator through UART ttySAC*, it's en device mode only.

[Igor]

On 9/1/2020 at 8:48 AM, r2d2r01 said:

As uart /dev/ttySAC2 is used by boot/kernel, /sbin/agetty has been renamed to stop its launching

With this you achieved nothing in your direction. You only disable getty on that connection. You need to tell u-boot and kernel to not use it for console. I am not sure you can make use of this UART without poking with u-boot and kernel DT.

 

And there is more to this - logic levels on this UART are not standard
https://forum.odroid.com/viewtopic.php?t=23181

[r2d2r01]

Thank's for answer, i aggree with u / uboot/kernel , I readen your answer on a other post to skip serial output during boot to use it.
In fact when i connect directly EXTDEV/XR21V14 to HC1/USB (rather through HC1/UART/CP2102N), kernel detect it and load driver/initiate communication, HC1 becomes the host with device and data transits fine.

On odroid site, it says voltage depends board (1.8v for XU*, 3,3v for C*), i measure 3;3 for HC1 wich is almost a XU4 (boot.ini)

 

[r2d2r01]

Other point, you can plug a usb switch with external power supply (5V/1A(*)) to HC1/USB and plug differents devices that's runs fine.

(*) depending consumption of devices (display=80ma..400mA (depending resolution/technology)), (wifi=0..250ma if active) / mouse/keyboard=~nothing / ...