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EKK-LM3S811 game example scrolling code

Posted by mthomas

on Oct 15 2006 10:14 AM

It's not that important since it's just about a "game example"-code but there seems to be a mistake in the code gs_ev-lm3s811.c which comes with the Keil MDK evaluation-version on the "Stallaris CD" V1.01 and is also present in the Driver-Library Version 852 which I have just downloaded from the web-site. The code seems to be a wrong here:

Code:



 
[...]
if(ulIdx <>96)
{
   for(ulLoop = 0; ulLoop <>ulIdx; ulLoop++)
   {
      g_pucFrame[ulLoop + 95 - ulIdx] =  
         pucImage[ulLoop];
[...]

When ulIdx reaches 96 and ulLoop is 0 the array-index is 0+95-96=-1. I found this when I compiled the example with the GNU-Toolchain (Codesourcery 2006-gq/gcc 4.1.0): the scrolling of the contest URL "freezes" when reaching the left side of the display (when ulIDX is 96). With a binary compiled with the RV-toolchain (from Keil MDK V3.03beta) the text scrolls completly. I wonder how the RV-toolchain could handle the "-1". Anyway: I have hopefully fixed this (starting with if (ulIDX<96)). at="" least="" the="" binary="" created="" with="" the="" gnu-toolchain="" now="" works="" as="" expected="" on="" the="">

http://www.siwawi.arubi.uni-kl.de/avr_projects/arm_projects/index_cortex.html

Martin Thomas

Post edited by: mthomas, at: 2006/10/15 10:14

Posted by englere

on Oct 16 2006 08:06 AM

Intellectual470 points

Thanks for this fix!

1) Do you have any idea when Cortex support will be rolled into the official WinArm chain?

2) Have you tried to compile the gcc sources from CodeSourcery? I looked at their code once but they didn't seem to have makefiles and it looked like a lot of work.

Posted by mthomas

on Oct 16 2006 09:11 AM

Prodigy180 points

englere wrote:

Thanks for this fix!
1) Do you have any idea when Cortex support will be rolled into the official WinArm chain?

I hope the Codesourcery-people will modify the
code-base for the "official" gcc soon but I do not have any information when this will happen. Will send an e-mail to codesourcery and ask about this.

2) Have you tried to compile the gcc sources from CodeSourcery? I looked at their code once but they didn't seem to have makefiles and it looked like a lot of work.

No, so far I have not tried to build gcc from the Codesourcery-sources since Codesourcery already provides precompiled binaries for Win32 hosts. The Codesourcery package and the GNU-toolchain that comes with WinARM can co-exist on the same machine (I have used the build-utils (make, sh) from WinARM (taken from the MinGW-project) and the GNU-Toolchain from Codesourcery to build the LMI driver-library and examples).

Martin Thomas

Posted by mthomas

on Oct 16 2006 09:11 AM

Prodigy180 points

Posted by Stellaris Brian

on Oct 26 2006 10:55 AM

Expert5380 points

Martin,

You are correct that this code is in error; thanks for reporting it. Interestingly, it works just fine with the version of CodeSourcery that we have in-house (well, it doesn't crash!). Wonder what has changed?

The actual fix to the code is the following:

Code:



 
        if(ulIdx <>96)
        {
            for(ulLoop = 0; ulLoop <>ulIdx; ulLoop++)
            {
                g_pucFrame[ulLoop + 96 - ulIdx] = pucImage[ulLoop];
                g_pucFrame[ulLoop + 96 - ulIdx + 96] =
                    pucImage[ulLoop + ulWidth];
            }
        }

I.e. the "ulLoop + 95" inside the loop is changed to "ulLoop + 96".

It is a subtle difference, one that you're very unlikely to actually notice when watching the display (especially since it is so small!). But, if you watch closely (or single step through the screen updates with a debugger) with the original code, you'll see that when it enters this section of code (i.e. when the scrolled image first appears from the right side of the display), the image does not utilize the far right column of the display. Once the image reaches the left side of the display, it will pause for one update (1/30th of a second) and then start utilizing the far right column of the display for the remainder of the scrolling.

The fix above corrects the scrolling behavior; the initial phase utilizes the far right column and there is no pause. This fix was incorporated into the latest release of the driver library, which was posted to the web site yesterday.

--Brian

Posted by mthomas

on Oct 26 2006 13:39 PM

Prodigy180 points

Thanks for the information and the "official" bug-fix.

Martin Thomas