Delay in SPI Transfer with STM32H7

[Roibert]

Dear Forum

Im using STM32 H755 ZI in the starter kit.

I set the Timer 4 for generate a Interrupt each 1ms.

At begin of INT:

     -I toggle a PIN,

      -and, send a SPI data (8 byte or 16..not important)

What I noted is a delay of almost 10uS beetwen pin toggle and begin of 1st bit TX from

SPI (begin of SPI transmission i means)

Some data:

FCPU=64M coming from internal 64M HSI

SPI1_CLK=4M coming from PER_CLK =64M  (with SPI prescaler=16  -->4M) 

FAPB=64M

Code inside INT Timer:

HAL_GPIO_TogglePin(PF10Test_GPIO_Port, PF10Test_Pin);

HAL_SPI_Transmit(&hspi1, p_Data16b, 1, 100);

__HAL_TIM_CLEAR_FLAG(htim4, TIM_FLAG_UPDATE);

Thanks for your help

Roberto

[Uwe Bonnes]

Probably __HAL_LOCK(hspi) inside HAL_SPI_Transmit() code takes some time...

[David Littell]

Are you sure about the core's clock rate?  How?

Is the instruction cache enabled and the Flash configured for best performance?

[AScha.3]

>What I noted is a delay of almost 10uS beetwen pin toggle and begin of 1st bit TX from

And ...?  You want it faster or what ?  at 64 MHz (with a 500MHz capable cpu ) ?

to see the speed of this cpu:

- set cpu clock (pll) to 400MHz (or so)

- set I-cache on/enable

- set optimizer to -O2 (or -Ofast, try.)

THEN check again. (and tell..) 🙂

[Roibert]

Thanks to all for reply

I removed the HAL, and write to the registers directly; now the dalay is 1us against 10us of before.

Now i will try to set cache,and will report all.

For now, my code is:

 SPI1->TXDR=(uint16_t)( 0x55AA);

SPI1->CR1 |=SPI_CR1_CSTART;

I dont need to test the .TXC because im transmitting in a INT timer of 1ms,( and sure, the transmission is already

gone before next INT of 1ms)

Thanks again

Roberto

[Roibert]

Some question again about SPI

As specified before, I configured the SPI as Master. I configurated also

the NSS as output driven by HW.

I noted that this out seem very sensitive to noise: when touch the oscilloscope input, 

the signal seem like it is float..Not very fix.   The same on MOSI out,and all this is tipical

when a HI Impedence is out. 

I think push pull is not hight impedence

Thanks very much

Roberto

[AScha.3]

Are you sure about good GND connections ?

Use a DMM and check ground from board to target - and to scope, if using it.

[Roibert]

Thanks for reply.

Im using the starter kit, NUCLEO-H755, and,as ground , I use the PIN5 of CN10.

This is digital ground .

Maybe the cable i connect to the pin are to long, but let me redo the connection

and close some device near the kit (monitor and so...maybe some noise).

I will tell you again

I ask another question about SPI.. As before, I launch a SPI data inside a INT TIMER  of 1ms

I set: 

DSIZE=16 bit  // 1 Frame=16bit

SPICLK=1US, so,  much more fast than 1ms of nexd data

Then in timer i send data:

INT_TIMER

{

//Load data

SPI1->TXDR=(uint16_t)( 0x55AA); 

//Start Tx

SPI1->CR1 |=SPI_CR1_CSTART;

...

}

When i do this, the data is shift out OK, but CLK is 32 --bit--long..Not 16

as i want.

So, i can use the the TSIZE =1,reladed by TSER .

So, in main:

main

{

set TSIZE=1

//Start SPI
SPI1->CR1 |= SPI_CR1_SPE;

}

AND in Timer:

{

    set TSER=1 ;

   //Load data

    SPI1->TXDR=(uint16_t)( 0x55AA);

   //Start Tx

    SPI1->CR1 |=SPI_CR1_CSTART;

}

In this way, I aspect that ,when FIFO empty , TSIZE will be reload with TSER=1

and the process continue forever.

What can i see is that data is ok, clk is long ok (16), CS also ok (H->L->H),but, this

work only 1 times..Then stop.

Look at register with IDE (after a breakpoint), i see TSIZE=1, TSER=1.

Why.

The HAL cen do this good because they START and STOP SPI via .SPE bit. But i think,

this will cost a lot of time to schut on/off the controller.

I would like reach is   : -Load FIFO with 16 bit, 

                                    -The SPI transmit this 16 bit delimitated by CS

                                    -..and so forever 🙂

Thanks for hel, and excure for long text

  Roberto

[David Littell]

It would probably be very helpful to review some of the examples provided with the HAL package.  Maybe get one (or more) of them built and running on your Nucleo.  Understand the principles first and only then try to make it run faster.

[Roibert]

Thanks Mr David for reply

I create a code with Hal, and code is working as i aspect...all OK

Because a big delay ,im triing to bypass HAL (hope is the correct solution.)

So, I also read all the datasheet about SPI ,register and flags, tryng to bypass

this problem. 

Looking code of the SPI HAL ,HAL_TRANSMIT(...) I understand  they modify at every 

call  the .TSIZE register,and this is possible, only if you disable SPI  (via   .SPE.)

IF we -dont- want to disable  and renable  SPI  at each TX, we can use the TSER register

that reload the TSIZE . This is what written in datasheet.

So, just for riassume all , i have 2 case: (  i report the code for sintetize all , so , dont need to scroll

previous post):

1) dont touch TSIZE:  In this case, the transmission work continue, but i get 32 bit clk

DSIZE=16 bit  // 1 Frame=16bit 

INT_TIMER

{

   //Load data

   SPI1->TXDR=(uint16_t)( 0x55AA); 

  //Start Tx

  SPI1->CR1 |=SPI_CR1_CSTART;

 .....

  }

2) Setting TSIZE and TSER:  In this casa i get Correct number of clk, but only 1 time,

then SPI stops.

INT_TIMER

{

     set TSER=1 ;

   //Load data

    SPI1->TXDR=(uint16_t)( 0x55AA);

   //Start Tx

    SPI1->CR1 |=SPI_CR1_CSTART;

}

What i would like to get, is that, i load FIFO with 1 or more frame, and SPI transmit each one,

with correct CLK and each one with his own CS movement .

Thanks for your time.

Roberto