USB adapters performance optimization

[FORScan]

Update February 2023 : The original article was created in 2015 and much outdated. Please do not spend your time trying to make the cheap adapters work. Instead of, please use recommended adapaters. Please find more information here:

What adapter should I purchase for FORScan for Windows?
Why should I use more expensive "recommended" adapter instead of regular ELM327?
What are possible problems if I use "regular" ELM327 instead of "recommended" adapter?


Main advantage of USB adapters against Bluetooth and WiFi ones is performance. But sometimes some optimization is necessary to reach the maximum of possible performance. Below we describe some tricks on how to improve USB adapter speed in FORScan.

FORScan shows some adapter parameters in the Vehicle section:

start_en.png (66.21 KiB) Viewed 122229 times

Minimum response time is most critical, as it in fact means adapter delay (time added to every request and response). In this case, it is not so bad, but this adapter may work better. Let's try to fix:

1. FTDI UBS 2 RS232 chips by default have odd 16ms delay reading data from buffer. Our luck is that It can be easilty reduced:

device_manager_en.png (134.65 KiB) Viewed 122229 times

Call Device Manager, find your USB port. (1) Call Properties; (2) Call advanced (3) Change Latency Timer from 16 to 2 or 1 ms.

PC reboot is recommended after this procedure.

This trick works only for FTDI chips. Prolific, Silicon Labs and others have no this latency timer problem.


2. If we check adapter performance now, we will see that minimal response time reduced from 16 to 10 ms:

after_ftdi_en.png (57.24 KiB) Viewed 122229 times

Well, it's better but still slow. Another improvement deal is to set the Auto-increase option is FORScan settings:

start_settings_en.png (66.71 KiB) Viewed 122229 times

Let's check it and re-connect:

end_en.png (48.25 KiB) Viewed 122229 times

We see great improvement now, FORScan has increased interface speed from 38,4 to 500 Kbps and minimal response time dropped from 10 to 2 ms. This is best reachable delay for china ELM327 USB adapters.

This way is applicable for all USB adapters. You may ask why this nice option is not enabled by default? Answer is simple: initially this option was enabled by default, but it freezes some china adapters, so we have disabled it.

[william]

Thanks tried this today and got very good improvement.

[Matt1295]

followed this guide and worked a treat 13 down to 2/3ms

[oldbob70]

were and how do you find this in the forscan program ?

[oldbob70]

were and how do you find this in the forscan program ?

[fred08155]

This has to be adjusted in Windows system settings (device manager). FORScan cannot do this for you. You have to do this by yourself.

[Airborne_Ape]

I made a 3min video to walk people through these exact steps:

https://youtu.be/8aRxgeOACEY

[d14u]

Thank you - found out this myself.

Chinese ELM327 now does 3ms and works like a charm.

[saeb]

For Windows 10

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\FTDIBUS\{Device VID, PID and serial number}\0000\Device Parameters\LatencyTimer

Change from 16 to 2.

[esqueue]

My experience with writing firmware with the OBDLink EX was a good learning experience. The connection was so slow that it would eventually outright fail, leaving me with a nonfunctional APIM.

It was after doing what's listed in this thread that it sped it up to a reasonable time and I was finally successful.