TMS320F28069M: Printf() takes 20ms to print a NewLine character with CCS debugger

Jakub Klein

Part Number: TMS320F28069M
Other Parts Discussed in Thread: DRV8301

Hi,

I am using DRV8301 kit with PICCOLO MCU and I'm testing the "printf()" function that sends data to the console view in my CCS.

I have done a few tests to see how much it takes to print the letters. Printf() was executed once per second from the main loop and CPU_TIME module was used to get the amount of cycles passed.

What I noticed is that printing a newline character ("/n") takes about 2 000 000 ticks, what equals to roughly 20ms at 90 MHz CPU frequency! This is unacceptable amount of time. For comparison, a carriageReturn ("\r") character takes only 400 ticks.

I have confirmed the result by looping the printf("\n") 50 times and toggling the LED afterwards - indeed, the LED blinked about once per second.

What's interesting, the timing seems to be OK after finishing the debugger.

So, the question arises - is it normal and is there any way to walk around this? I thought about using "\r" instead, but I still need at least one "\n" somewhere in the code (otherwise the function will not print at all).

over 8 years ago

0 Brett Larimore over 8 years ago

TI__Guru 57255 points

Hi Jakub,

Please see the following thread. Using SCI/UART instead, as Richard mentions, is a relatively common alternative method.
https://e2e.ti.com/support/microcontrollers/c2000/f/171/t/601591

Note that if your goal is really just to see the value of variables in real-time, as code is running, you can use real-time mode along with the expressions (or watch) window within CCS.
http://processors.wiki.ti.com/index.php/Real-Time_Mode
https://www.youtube.com/watch?v=gVDRo9m-4ng (specifically the area around 8:30)

Hopefully this helps!

Thank you,
Brett

0 Jakub Klein over 8 years ago in reply to Brett Larimore

Intellectual 630 points

Thank you, that's a great dose of helpful information.

I know I can view the variables in CCS, but I need some human interface for displaying information during the program run-time (preferably in absence of CCS). I can't use additional UART port as I have all of them used in the design...

Will the problem remain if I use "printf" to display information on some external terminal (Ex. Tera-Term) with no CCS debugger connected? What I thought about is: http://processors.wiki.ti.com/index.php/Using_the_serial_adapter_of_XDS100

0 Brett Larimore over 8 years ago in reply to Jakub Klein

TI__Guru 57255 points

Hi Jakub,

I don't know enough about Tera-Term's various options, but I don't think you'll be able to get it to utilize the JTAG interface. Most terminal programs utilize a UART connection. Even if you did, my understanding is that the use of printf will always cause issues.

I'd instead highly recommend utilizing some unused peripheral to make the human connection you need. If you're not using the native USB peripheral on the F28069M device, that may be a good option. Another option could be CAN.

Thank you,
Brett

0 Jakub Klein over 8 years ago in reply to Brett Larimore

Intellectual 630 points

Hi,

By using XDS100 I thought about port B of the adaptor that is available to use as an UART. Although now I am afraid that it might be simply redirecting one of the two SCI ports anyways (that I don't have left)...

Maybe I'll use i2c bus with some i2c-to-usb converter. Is there any risk I will notice similar issues (or other delays)?

0 Brett Larimore over 8 years ago in reply to Jakub Klein

TI__Guru 57255 points

Hi Jakub,

Your conclusions that Port B of the FTDI chip will use up an SCI port is correct.

I2C is a relatively slow interface, and so I'd recommend measuring it against your desired data rate to the human interface. However, utilizing any peripheral, will not stall the C28x (like printf). For I2C & many of the peripherals, your driver is likely to be relatively light - this means you save your cycles for controlling a motor or whatever you're controlling.

Thank you,
Brett

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TMS320F28069M: Printf() takes 20ms to print a NewLine character with CCS debugger