SPI support to other libraries using TRANSMIT ONLY or RECEIVE ONLY

[AndreoBotelho]

Describe the bug
stm hang when trying to send data to SPI bus

To Reproduce

#include <SPI.h>

#define TFT_MOSI PE14
#define TFT_SCLK PE12
#define TFT_CS   PE4  // Chip select control pin
#define TFT_DC   PE13  // Data Command control pin
#define TFT_RST  PE11  // Reset pin (could connect to RST pin)
#define TFT_BL   PC7  // bl pin (could connect to bl pin)


void setup() {
  Serial.begin(115200);
  pinMode(TFT_CS, OUTPUT);
  pinMode(TFT_DC, OUTPUT);
  pinMode(TFT_BL, OUTPUT);
  digitalWrite(TFT_BL, LOW);  
  digitalWrite(TFT_CS, LOW);  
  digitalWrite(TFT_DC, LOW);  
  SPI.setMOSI(TFT_MOSI);
  //SPI.setMISO(PE5);
  SPI.setSCLK(TFT_SCLK);
  SPI.setClockDivider(2);
  SPI.begin();
  Serial.println("Inited");
}

// the loop function runs over and over again forever
void loop() {

  Serial.println("Loop");
  digitalWrite(TFT_BL, HIGH);  // turn the LED on (HIGH is the voltage level)
  digitalWrite(TFT_CS, LOW);  
  SPI.transfer(0x21, true);
  digitalWrite(TFT_CS, HIGH);  
  delay(1000);                      // wait for a second
  digitalWrite(TFT_CS, LOW);  
  digitalWrite(TFT_BL, LOW);   // turn the LED off by making the voltage LOW
  SPI.transfer(0x28, true);
  digitalWrite(TFT_CS, HIGH);  
  delay(1000);  // wait for a second
}

Steps to reproduce the behavior:

1. power on

Expected behavior
send bytes to display

Screenshots
N/A

Desktop (please complete the following information):

• OS: Windows
• Arduino IDE version: 2.3.2
• STM32 core version: latest
• Tools menu settings if not the default: default
• Upload method: DFU

Board (please complete the following information):

• Name: STM32H743 custom board
• Hardware Revision: none
• Extra hardware used if any: SPI ST7789 display

Additional context
SPI.setClockDivider(int); is not working, I can get only 256 divider, manually coding 2 divider works fine
uncommenting //SPI.setMISO(PE5); make it works but I don't have this MISO pin connected and loses a GPIO on PE5

are there any plans to support DMA transfer? the current code is slow and eats a lot of cpu power.

[fpistm]

Hi @AndreoBotelho
about setClockDivider it should not be used, you have to use SPISettings:
https://www.arduino.cc/reference/en/language/functions/communication/spi/setclockdivider/

[fpistm]

About your issue with clock divider did you check the clock config?
About the need of miso, yes it is required to properly init the SPI:

Arduino_Core_STM32/libraries/SPI/src/utility/spi_com.c

Lines 222 to 226 in 3a3ff84

	/* Pins MOSI/MISO/SCLK must not be NP. ssel can be NP. */
	if (spi_mosi == NP || spi_miso == NP || spi_sclk == NP) {
	core_debug("ERROR: at least one SPI pin has no peripheral\n");
	return;
	}

About DMA, it is not planned. Anyway, feel free to contribute 😉

I see no specific issue (except maybe the clock divider) so what did you expect?