Can anyone provide a link to a currently available and confirmed working USB to 3.3V TTL converter that works at 1500000 bps? The PL2303 I have technically supports up to 3 Mbps but only in certain discrete steps, and 1500000 is not one of those steps. The MCP2221A only supports up to 460800 bps. The FTDI FT232 data sheet claims support up to 3 Mbps but is unclear about whether arbitrary baud rates are supported, or only discrete steps like the PL2303. Searching for a compatible USB-TTL cable to work with the RK3399 has been futile so far. A link to a confirmed working cable would be much appreciated. Confirmed working cables only. No theoretical devices, please.

1 hour ago, drice said:

Searching for a compatible USB-TTL cable to work with the RK3399 has been futile so far.

I am using a few of those. I am sure some cheap from Ebay must work as well (in specs its written Baud rates: 300 bps to 1.5 Mbps).

 

... and two from Radxa. Confirmed operational with RK3399.

lsusb

0403:6001 Future Technology Devices International, Ltd FT232 USB-Serial (UART) IC

 

Thanks, I'll get one of those.

1 hour ago, drice said:

Searching for a compatible USB-TTL cable to work with the RK3399 has been futile so far.

I've almost all my boards hooked up with either FDTI, PL2x0x but mostly CH340 and work well with all my boards, including RockPro64, RockPi, OPi-RK3399.

The only one that bother me is the NanoPCT4, where USB-TTL RX works Ok but not TX, so I can't stop U-boot for example.

This NanoPCT4 issue is probably due to a protective resistor R252 which is a 2K2, I will probably try one day to short that one to see if is it the cause ...

According to the FT232R documentation (https://ftdichip.com/wp-content/uploads/2020/08/DS_FT232R.pdf), the chip is capable of 1500000 baud.  Maybe it's just a buggy driver or OS that prevents you from activating that speed.  (It failed for me on macOS 11.1, but worked in Linux.)