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DK-TM4C129X: Flashing TFT display in raster mode

user1208537
Prodigy 30 points
Part Number: DK-TM4C129X


The raster mode is set. DMA is on. Ping-Pong is not used.
If we change the picture pixel by pixel, then everything is fine, but if we update it with a block, for example, symbol 44 font, the display blinks. There is an interrupt DMA FIFO Underflow. Apparently interrupted LCD DMA
At what point can we write to the buffer to avoid interrupting the DMA?

  • 0
    TI__Guru**** 191906 points
    Hi,

    Please use ping-pong DMA mode as using two frame buffers enables the simultaneous operation of outputting the current raster data to the display and updating the next frame of data. Please try and see if it makes a difference. I believe the ping-pong approach is preferred in most applications.
  • 0 in reply to Charles Tsai
    Prodigy 30 points
    Hi Charles,

    Forgot to write that I use SDRAM. The Frame0 and the Frame1 will be in the SDRAM. Writing in the Frame1 causes an interrupt DMA FIFO Underflow. The problem is possible in the simultaneous access of LCD DMA and CPU to the SDRAM

    regards,
    Denis
  • 0
    Guru 117855 points

    Firm/I "know little" of this vendor's '129.     (yet have designed - and sold - many thousands of such displays & graphic controllers)

    It is usual that:

    • there exist,  "Marked Safe Periods" - in which you may perform Screen Writes - MINUS   "Display Contention"
    • often those "Safe Periods" prove  "Duration Limited" - you must insure that your Screen Writes do not persist beyond that limit.    

    Should this (the latter, above) prove YOUR CASE - you must:

    • attack immediately upon the arrival of the "Safe Period's MARK"
    • experimentally determine  - or note from the spec - the maximum duration of such "Safe Period" - and then,  "Limit your Screen Writes" - so as to meet that specification

    As your issue arrives (only) when a "data block"  ("symbol 44 font") - which appears (beyond the capacity) of  your device/system - is passed - it is clear that your "Safe Write Duration" has been exceeded!    In such case - you must "Reduce the Size of the Transfer" and/or "Attack Immediately" - when your system signals,  "Ready."   (ideally - do both!)

    Serious Display Controllers - and more advanced ARM MCUs - well provide for such needs -  (even)  avoiding the requirements for "Safe Periods."

    Should it NOT be noted - that thread's title,  "Flashing  TFT in Raster Mode" - strays far (very far) OFF MARK?

  • 0 in reply to cb1_mobile
    Prodigy 30 points

    We have experience with LCD

    In which register there is a flag that signals the possibility of writing?

    There are no flags signaling "Ready"

    The documentation does not describe the simultaneous operation of EPI and LCD DMA

  • 0 in reply to user1208537
    Guru 117855 points

    If those "normal/customary"  "High Speed - Write to the Display w/out CONTENTION" Signals are ABSENT - might that signal the inability of such device to,  "Meet your Performance Objectives?"

    Should you "re-read" my writing - I provided the "general strategy" employed by  "Display Controllers"  (and Advanced MCUs) which take "Special Efforts" to AVOID Display Contention.     I noted my lack of "interest or usage" in vendor's MCU -  (3 words in) - to my response.

    If those "Contention-Avoiding" signals are absent - then your best bet is to employ a "Reduced Pixel & Color Display" - OR - in your case - (as I earlier described) - you must break your "Symbol 44  Font" down into a,  "Series of multiple, smaller portions - sending ONLY those" -  in the "hope" of  avoiding - or at least minimizing - the unwelcome artifacts caused by Display Contention!      (again - there ARE ARM Cortex M4 MCUs - which  "Anticipate & AVOID" Display Contention ...)

    May it be noted that the (continued) usage of  "FLASHING TFT" w/in your Subject Line - appears (pardon) meaningless.     (or requires good clarification...)