void myTest(String str){} -> drawing problem

[Sascha8]

My 2x 64x32 panels chained to a 128x32 working really great on an ESP32. Thank you for the great lib!

But when I declare an procedure with an arduino String parameter and call it, the display each time draws just one single line at row0 and row 15.

void myTest(String str) {}

Can somebody please explain whats the reason? chatGPT and Gemini both talking about heap fragmentation and DMA timing issues. This makes me wonder, as I can use wifi, mqtt, OTA and other stuff without any drawing probs. getFreeHeap() returns 289748 at the program below .

void setup() {
  HUB75_I2S_CFG mxconfig(PANEL_RES_X,PANEL_RES_Y,PANEL_CHAIN);
  mxconfig.clkphase = false;
  mxconfig.driver = HUB75_I2S_CFG::FM6124;

  dma_display = new MatrixPanel_I2S_DMA(mxconfig);
  dma_display->begin();
  dma_display->setBrightness8(20); //0-255
  dma_display->clearScreen();
  delay(200);
  dma_display->setTextSize(1, 1);
  dma_display->setCursor(0, 0); dma_display->println("Hello");
  myTest("");  //doesn't mater if I call it after or before panel init. (Using const char* str works fine)
}

void loop() {
  delay(20);
}

void myTest(String str) {
// do nothing
}

Debug log:
MinFreeHeap:326744
FreeHeap:332416
[ 541][I][ESP32-HUB75-MatrixPanel-I2S-DMA.h:448] begin(): [begin()] Using GPIO 25 for R1_PIN
[ 552][I][ESP32-HUB75-MatrixPanel-I2S-DMA.h:449] begin(): [begin()] Using GPIO 26 for G1_PIN
[ 561][I][ESP32-HUB75-MatrixPanel-I2S-DMA.h:450] begin(): [begin()] Using GPIO 27 for B1_PIN
[ 569][I][ESP32-HUB75-MatrixPanel-I2S-DMA.h:451] begin(): [begin()] Using GPIO 14 for R2_PIN
[ 577][I][ESP32-HUB75-MatrixPanel-I2S-DMA.h:452] begin(): [begin()] Using GPIO 12 for G2_PIN
[ 586][I][ESP32-HUB75-MatrixPanel-I2S-DMA.h:453] begin(): [begin()] Using GPIO 13 for B2_PIN
[ 594][I][ESP32-HUB75-MatrixPanel-I2S-DMA.h:454] begin(): [begin()] Using GPIO 23 for A_PIN
[ 602][I][ESP32-HUB75-MatrixPanel-I2S-DMA.h:455] begin(): [begin()] Using GPIO 19 for B_PIN
[ 611][I][ESP32-HUB75-MatrixPanel-I2S-DMA.h:456] begin(): [begin()] Using GPIO 5 for C_PIN
[ 619][I][ESP32-HUB75-MatrixPanel-I2S-DMA.h:457] begin(): [begin()] Using GPIO 17 for D_PIN
[ 627][I][ESP32-HUB75-MatrixPanel-I2S-DMA.h:458] begin(): [begin()] Using GPIO -1 for E_PIN
[ 635][I][ESP32-HUB75-MatrixPanel-I2S-DMA.h:459] begin(): [begin()] Using GPIO 4 for LAT_PIN
[ 644][I][ESP32-HUB75-MatrixPanel-I2S-DMA.h:460] begin(): [begin()] Using GPIO 15 for OE_PIN
[ 652][I][ESP32-HUB75-MatrixPanel-I2S-DMA.h:461] begin(): [begin()] Using GPIO 16 for CLK_PIN
[ 661][I][ESP32-HUB75-MatrixPanel-leddrivers.cpp:50] fm6124init(): [LEDdrivers] MatrixPanel_I2S_DMA - initializing FM6124 driver...
[ 673][I][ESP32-HUB75-MatrixPanel-I2S-DMA.h:472] begin(): [begin()] HUB75 effective display resolution of width: 128px height: 32px.
[ 685][I][ESP32-HUB75-MatrixPanel-I2S-DMA.cpp:43] setupDMA(): [I2S-DMA] Free heap: 332204
[ 693][I][ESP32-HUB75-MatrixPanel-I2S-DMA.cpp:44] setupDMA(): [I2S-DMA] Free SPIRAM: 0
[ 701][I][ESP32-HUB75-MatrixPanel-I2S-DMA.cpp:71] setupDMA(): [I2S-DMA] Allocating 32768 bytes memory for DMA BCM framebuffer(s).
[ 713][I][ESP32-HUB75-MatrixPanel-I2S-DMA.cpp:85] setupDMA(): [I2S-DMA] Minimum visual refresh rate (scan rate from panel top to bottom) requested: 60 Hz
[ 727][W][ESP32-HUB75-MatrixPanel-I2S-DMA.cpp:105] setupDMA(): [I2S-DMA] lsbMsbTransitionBit of 0 gives 28 Hz refresh rate.
[ 738][W][ESP32-HUB75-MatrixPanel-I2S-DMA.cpp:105] setupDMA(): [I2S-DMA] lsbMsbTransitionBit of 1 gives 55 Hz refresh rate.
[ 749][W][ESP32-HUB75-MatrixPanel-I2S-DMA.cpp:105] setupDMA(): [I2S-DMA] lsbMsbTransitionBit of 2 gives 100 Hz refresh rate.
[ 760][W][ESP32-HUB75-MatrixPanel-I2S-DMA.cpp:118] setupDMA(): [I2S-DMA] lsbMsbTransitionBit of 2 used to achieve refresh rate of 60 Hz. Percieved colour depth to the eye may be reduced.
[ 776][I][ESP32-HUB75-MatrixPanel-I2S-DMA.cpp:121] setupDMA(): [I2S-DMA] DMA frame buffer color depths: 8
[ 786][I][esp32_i2s_parallel_dma.cpp:456] allocate_dma_desc_memory(): [ESP32/S2] Allocating memory for 512 DMA descriptors.
[ 797][W][esp32_i2s_parallel_dma.cpp:544] create_dma_desc_link(): [ESP32/S2] Creating final DMA descriptor and linking back to 0.
[ 809][I][ESP32-HUB75-MatrixPanel-I2S-DMA.cpp:234] setupDMA(): [I2S-DMA] Created 512 DMA descriptors for buffer 0.
[ 819][I][esp32_i2s_parallel_dma.cpp:126] config(): [ESP32/S2] Performing config for ESP32 or ESP32-S2
[ 828][I][ESP32-HUB75-MatrixPanel-I2S-DMA.cpp:301] setupDMA(): [I2S-DMA] DMA setup completed
[ 840][I][esp32_i2s_parallel_dma.cpp:133] init(): [ESP32/S2] Performing DMA bus init() for ESP32 or ESP32-S2
MinFreeHeap:288616
FreeHeap:289748

[mrcodetastic]

ChatGPT and Gemini are just hallucinating some random reason.

The first thing you should probably do though, is run this example to check that each pixel is being addressed correctly. If it is, then it's not an issue with this code and something funky with the length of the text you're trying to print.

I can't see from the code you're provided what is being printed in any case to explain your issue.

Ihttps://github.com/mrcodetastic/ESP32-HUB75-MatrixPanel-DMA/tree/master/examples/Pixel_Mapping_Test

[Sascha8]

I know, AI like to talk strange stuff at strange problems. But nevertheless - the problem is there, 100% reproducible.
The simplest HelloWorld works fine, but if I outsource the print() to a simple function like:

void doPrintText(String str) {
  dp->Print(str);
}

I always get garbage on the matrix.

[board707]

dp->Print(str);

The C++ is a case-sensitive. The print() and Print() are two different methods. May be calling the print() will got you a better results?

[Sascha8]

Thanks for your replies!
I know this problem sounds really strange. I’m not a C++ expert (so I still like to use the convenient String class), but I’ve done many working IoT projects on the Arduino ESP32 in the past.

I wrote the sample code above from memory – sorry for the typo – of course I used print().
The length of the text to print doesn’t matter. Even a doPrintText("") makes the problem visible. In the meantime, I changed all my internal libraries (written over the years) to use a const char* instead of String, and now everything works fine. But the root cause is still there, and I’d really like to understand what’s happening here! I never had a similar issue with the String class before.

Apparently, no one else has this problem – or am I the only one still using the Arduino String class?

If I can provide more specific information about my issue, please let me know how. Thank you!

[board707]

If I can provide more specific information about my issue, please let me know how.

Could you provide a full test code (with setup() and loop() matrix init etc...) which others could to run to check the issue?

[Sascha8]

Sure.
Recreating this HelloWorld from scratch gives a new hint - The problem occurs only if "CoreDebugLevel" is set to anything other than NONE!
That sounds even more strange. So I didn't need to change the code - just switch the CoreDebugLevel to NONE to be able to use the Arduinos String class.

#include <SPI.h>
#include <Wire.h>
#include <gfxfont.h>
#include "GFX_Lite.h"
#include <ESP32-VirtualMatrixPanel-I2S-DMA.h>

#define PANEL_RES_X 64      // Number of pixels wide of each INDIVIDUAL panel module. 
#define PANEL_RES_Y 32     // Number of pixels tall of each INDIVIDUAL panel module.
#define PANEL_CHAIN 2      // Total number of panels chained one to another

MatrixPanel_I2S_DMA* dma_display = nullptr;


void setup() {
  Serial.begin(115200);
  delay(500);

  HUB75_I2S_CFG mxconfig(PANEL_RES_X,PANEL_RES_Y,PANEL_CHAIN);

  mxconfig.clkphase = false;  // Needed to remove "ghosting"
  mxconfig.driver = HUB75_I2S_CFG::FM6124;
  mxconfig.i2sspeed = HUB75_I2S_CFG::HZ_8M;  //Needed to avoid some flickering of some pixels in some rows in the 2nd panel
  dma_display = new MatrixPanel_I2S_DMA(mxconfig);
  bool res = dma_display->begin();
  Serial.print("begin()="); Serial.println(res);
  
  dma_display->setBrightness8(20); 
  dma_display->clearScreen();
  dma_display->setTextSize(1, 1);
  dma_display->setCursor(5, 20); 
  dma_display->print("Test1"); 
  printString("Test2");
}


void printString(String str) {
  //dma_display->print(str);   //Yes, even if it is commented out, error occurs!
}

void loop() {
  delay(20);
 }

No error:

Error:

I can provide the debug outputs from the verbose build if it is interesting.

[board707]

The problem occurs only if "CoreDebugLevel" is set to anything other than NONE!

It seems this isn't a bug in the panel's code, but some internal issues with the ESP32 package.
In that case, please forgive me, but I won't delve into it further. Perhaps @mrcodetastic might be interested.
Hope you will fix the issue.

[Sascha8]

Thank you for listening – it really helped me to find the workaround. It would be interesting if you could confirm this strange behavior on your system.
Maybe it’s related to IDF and DMA – there are many in-depth comments in esp_log.h.
For reference: I’m currently using idf-release_v5.4-858a988d-v1.