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back channel latency

Mark Jeffree
Prodigy 80 points
Other Parts Discussed in Thread: MSP-EXP430FR5994

Host: CCS Version 6.2.0.00050 running on Win7 64 bit

Target: MSP-EXP430FR5994 LaunchPad

There are other questions on the forum about back channel latency, but I don't think they are about the same issue.

I am using the backchannel UART to interactively poke at my program running on the MSP430 target. The backchannel is a virtual COM port provided over USB. When I look at the Driver Properties it shows me

MSP Application UART1 (COM6)

Driver Provider:   Texas Instruments

Driver Date:         27/10/2016

Driver Version:    1.6.0.0

If I look at the Driver Details from that dialog box, I see

Provider:      Microsoft Corporation

File version: 6.1.7601.18247 (win7sp1_gdr.130828-1532) 

So it's not entirely clear whether it is a TI or Microsoft driver.

My terminal program is PuTTy and I'm using very mild settings of 9600 baud. The virtual UART functions happily in both directions, BUT there is about a 1s lag in character echo. It's the same if I use the CCS terminal window. This could be latency in the USB driver on the host or it could be in the target emulator processing loop.

I can't find any latency settings in the host driver configuration. Is there anything I can do to cut this latency other than moving to an external FTDI?

- Mark

  • 0
    TI__Guru**** 216657 points
    Hi Mark,

    Try exiting the debugger session or free-run the device, the SBW communication used for debugging purposes typically causes the backchannel UART delay you've described. This disappears once the SBW can no longer hold down the device.

    Regards,
    Ryan
  • 0 in reply to Ryan Brown1
    Prodigy 80 points

    Thanks for the advice. Now I just hit RESET after the download and go from there. It's a much better experience.

    -- Mark

  • 0
    Guru 316430 points
    As for the driver information: USB CDC is a standard protocol, and the actual driver is from Microsoft and shipped with Windows; TI just provides an .inf file that points to that driver.
  • 0
    Guru 34483 points

    Mark Jeffree said:

    My terminal program is PuTTy and I'm using very mild settings of 9600 baud. The virtual UART functions happily in both directions, BUT there is about a 1s lag in character echo. It's the same if I use the CCS terminal window. This could be latency in the USB driver on the host or it could be in the target emulator processing loop.

    If the system has 1 second lag at 9600 bps (that is very low / lite rate) in character echo, than I will call it not usable during debugging. This is related to FET's firmware CDC - UART bridge implementation.

    BTW, For 5xx devices there is SBW / JTAG Mailbox system (faster than 9600 bps for sure) that can be used for logging, but it is not supported by TI FET's.

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