SPI Speed delay nucleo H755

[Igneous]

Good day,

I've been working on getting an external adc on the nucleo H755ziq to work at max speed. The adc can reach up to 1 million samples a second with a clock cycle time of 10ns. Problem is that it's only seeming to go at a speed of 60ns per clock cycle. Spi is set at 200mhz with a /2 prescaler on an external 48mhz crystal. Any idea why it's getting this 60ns speed instead of 10ns? Ive set the GPIO for spi to very high speed as well encase that was the issue.

[AScha.3]

Hi,

not clear : you have an  external adc at 1 Msps . Why ( internal 16b ADC can do this also ) ?

+

SPI at 100Mbit set (bit high...for 1 Ms conversion rate - or not ?) - but runs 6x slower - right ?

 

Did you check with MCO , the internal clock is what you expect ?

[Igneous]

It's an external ADC bc of a project Im working on that I can't specify more about. It's a custom ADC is as much as I can say. The important part is that, when checking the speed in the code, it shows the correct speeds of 100mhz for the spi (simply checked with HAL_RCC_GetPCLK2Freq()). meanwhile the logic analyser shows the speed of 60ns per clock cycle which suggests a 16.667mhz speed instead. It's like a 6x prescaler is added on or something. 

[AScha.3]

Ok,

so what is set as prescaler for this spi ?

see in your main: (example on spi4)

static void MX_SPI4_Init(void)
{

 /* USER CODE BEGIN SPI4_Init 0 */

 /* USER CODE END SPI4_Init 0 */

 /* USER CODE BEGIN SPI4_Init 1 */

 /* USER CODE END SPI4_Init 1 */
 /* SPI4 parameter configuration*/
 hspi4.Instance = SPI4;
 hspi4.Init.Mode = SPI_MODE_MASTER;
 hspi4.Init.Direction = SPI_DIRECTION_2LINES;
 hspi4.Init.DataSize = SPI_DATASIZE_8BIT;
 hspi4.Init.CLKPolarity = SPI_POLARITY_LOW;
 hspi4.Init.CLKPhase = SPI_PHASE_1EDGE;
 hspi4.Init.NSS = SPI_NSS_SOFT;
 hspi4.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_2;
 hspi4.Init.FirstBit = SPI_FIRSTBIT_MSB;
 hspi4.Init.TIMode = SPI_TIMODE_DISABLE;

...here prescaler /2 , so look, whats in your xx.init .

+

If this looks good, check with a scope on MCO , the internal clock is really what you expect !

[Saket_Om]

Hello @Igneous 

Could you share with us your system clock config please?

[Igneous]

this should do for that