3-wireSPI for SAMD21

General Discussion
1

Basic Information:

Printer Model: Customized
MCU : SAMD21
klippy.log (14.4 KB)

I try to set SERCOM4 to 3-wireSPI (MOSI, CLK, CS, without MISO)
according document
https://www.klipper3d.org/Config_Reference.html?h=samd#samd_sercom
rx_pin is optional. but I got “Invalid SERCOM configuration” issue.
while I comment out “rx_pin” (#rx_pin: PA12)

So, How could I set printf.cng to disable MISO at SERCOM4 ?
this pin(PA12) is use for dc_pin at SSD1306.

[samd_sercom sercom4_spi]
sercom: sercom4
clk_pin: PB11
tx_pin: PB10
#rx_pin: PA12

[display]
lcd_type:ssd1306
spi_bus:sercom4
cs_pin:PA13
dc_pin:PA12
reset_pin: PA27

2

Unfortunately, the Klipper code today does not support 3 wire spi mode. The rx_pin is documented as “optional” only because it is not needed when using i2c mode - it is required in spi mode.

-Kevin

3

I just modify sercom_spi_pins(uint32_t sercom_id)
at /src/atsamd/sercom.c
now, the SAMD21 could support Output Only SPI.
CS, CLK and MOSI. without MISO
For your reference,

#define VALID 0x0f // Dummy for Check Data
struct sercom_pin {
    uint8_t pins[3];
    uint8_t isvalid[3];
};

uint32_t
sercom_spi_pins(uint32_t sercom_id)
{
    if (sercom_id >= ARRAY_SIZE(sercom_pins))
        shutdown("Invalid SERCOM bus");

		const struct sercom_pad *tx_sp = NULL;
		const struct sercom_pad *rx_sp = NULL;
		const struct sercom_pad *clk_sp = NULL;
		uint8_t tx_pin = 0;
		uint8_t clk_pin = 0;
		uint8_t rx_pin = 0;
      
    tx_pin = sercom_pins[sercom_id].pins[TX_PIN];
    tx_sp = sercom_lookup_pad(sercom_id, tx_pin);
		gpio_peripheral(tx_pin, tx_sp->ptype, 0);
		
    clk_pin = sercom_pins[sercom_id].pins[CLK_PIN];
    clk_sp = sercom_lookup_pad(sercom_id, clk_pin);
		gpio_peripheral(clk_pin, clk_sp->ptype, 0);

		if (sercom_pins[sercom_id].isvalid[RX_PIN] == VALID) 
		{
			rx_pin = sercom_pins[sercom_id].pins[RX_PIN];
    	rx_sp = sercom_lookup_pad(sercom_id, rx_pin);
    	gpio_peripheral(rx_pin, rx_sp->ptype, 0);
		}			

    uint8_t dopo = sercom_lookup_spi_dopo(tx_sp->pad, clk_sp->pad);
    
    if (sercom_pins[sercom_id].isvalid[RX_PIN] != VALID) 
		{
    	if (rx_sp->pad == tx_sp->pad || rx_sp->pad == clk_sp->pad)
    		shutdown("Sercom RX pad collides with TX or CLK pad");
    		return SERCOM_SPI_CTRLA_DOPO(dopo);
		}	
		
		else
		{
				return SERCOM_SPI_CTRLA_DIPO(rx_sp->pad) | SERCOM_SPI_CTRLA_DOPO(dopo);
		}
}