The signal result becomes a straight line on the DAC

[macam1]

 

"I am using your program and made some changes, but when I use it in the function

 

 

HAL_DAC_Start_DMA(&hdac, DAC_CHANNEL_1, (uint32_t*)value, 89, DAC_ALIGN_12B_R); 
HAL_TIM_Base_Start(&htim4);

 

the signal result on the oscilloscope is not continuous. What I mean is, when I use a very long array, the result does not match what I expected. To help you understand, I am attaching two photos comparing the result I want and the result from the program.

 

I have a signal result like the one on the left, but I want it to be like the one on the right. After investigating, it turns out that the length value in HAL_DAC_Start_DMA was manually changed. If it can be done automatically, please give suggestions so I don't have to set it manually.

program to check

 

uint16_t hold_samples = 50;
uint16_t firstHalf[64] =
{
2100, 2149, 2250, 2350, 2450, 2549, 2646, 2742, 2837, 2929, 3020, 3108, 3193, 3275, 3355,
3431, 3504, 3574, 3639, 3701, 3759, 3812, 3861, 3906, 3946, 3982, 4013, 4039, 4060, 4076,
4087, 4094, 4095, 4091, 4082, 4069, 4050, 4026, 3998, 3965, 3927, 3884, 3837, 3786, 3730,
3671, 3607, 3539, 3468, 3394, 3316, 3235, 3151, 3064, 2975, 2883, 2790, 2695, 2598, 2500,
2400, 2300, 2199, 2098

}; // Nilai pada bagian pertama
uint16_t secondHalf[71] =
{
1997, 1896, 1795, 1695, 1595, 1497,1305, 1212, 1120, 1031, 944, 860, 779, 701, 627,
556, 488, 424, 365, 309, 258, 211, 168, 130, 97, 69, 45, 26, 13,4, 0, 1, 8, 19, 35, 56, 82,
113, 149, 200, 283, 336, 394, 456, 521, 591, 664, 740, 820, 902, 987, 1075, 1166, 1258,
1353, 1449, 1546, 1645, 1745, 1845, 1947, 1965, 1990, 2010, 2022, 2047
}; // Nilai pada bagian kedua
uint16_t totalSize = (sizeof(firstHalf) / sizeof(uint16_t)) + hold_samples + (sizeof(secondHalf) / sizeof(uint16_t));
 uint16_t index = 0;
 uint16_t n_firstHalf = (sizeof(firstHalf) / sizeof(uint16_t));

 for (int i = 0; i < n_firstHalf; i++) {
 value[index] = firstHalf[i];
 index++;
 }

 for (int i = 0; i < hold_samples; i++) {
 value[index] = 2048;
 index++;
 }

 int n_secondHalf = (sizeof(secondHalf) / sizeof(uint16_t));
 for (int i = 0; i < n_secondHalf; i++) {
 value[index] = secondHalf[i];
 index++;
 }

HAL_DAC_Start_DMA(&hdac, DAC_CHANNEL_1, (uint32_t*)value, 89, DAC_ALIGN_12B_R);
HAL_TIM_Base_Start(&htim4);

 

[LCE]

1) Is the DMA in CIRCULAR mode?

2) you probably need to add the hold value to the end of the array

 

And please post source code with the "</>" button to make it more readable. And you can still edit your original post.

 

PS / edit: and the DAC can't draw stuff, so it's not "a straight line", it's a DC voltage. ;) 

[macam1]

@LCE 

 

1. yes, DMA in circular mode

2. Can you give an example of what you mean? I'm a beginner and can't quite picture it. I just want to learn. Thank you for your feedback, I have already changed the output display.

[TDK]

> HAL_DAC_Start_DMA(&hdac, DAC_CHANNEL_1, (uint32_t*)value, 89, DAC_ALIGN_12B_R);

You're sending more than 89 values. Shouldn't this be

HAL_DAC_Start_DMA(&hdac, DAC_CHANNEL_1, (uint32_t*)value, index, DAC_ALIGN_12B_R);

 

Is the value array of sufficient size? Needs to be 64 + 50 + 71 samples long, of type uint16_t. Your code does not include its definition.

[macam1]

Yes, I have tried using

HAL_DAC_Start_DMA(&hdac, DAC_CHANNEL_1, (uint32_t*)value, index, DAC_ALIGN_12B_R);

but there is no result. That's why I tried using a fixed number. Is there something wrong with my code? Because when I add a watch for index, it shows 'not evaluated'. I'm a bit confused, please help.

@TDK 

[TDK]

Show the full code. Attach it as a 7zip file if needed. No reason why index should not work. Make sure you're using circular DMA.

[LCE]

The way you fill the array right now is:

firstHalf, hold_samples, secondHalf

From what you have shown what you want you might want to add hold_samples to the end.

But first you have to make the DMA run continously.