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Merged
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Sep 19, 2025
Merged

Allow SPI to disable RX or TX pins #3141

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3 changes: 3 additions & 0 deletions cores/rp2040/Arduino.h
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Original file line number Diff line number Diff line change
Expand Up @@ -170,6 +170,9 @@ constexpr uint64_t __bitset(const int (&a)[N], size_t i = 0U) {
#define __FIRSTANALOGGPIO 26
#endif

// For peripherals where a pin may be not used
#define NOPIN ((pin_size_t) 0xff)

#ifdef __cplusplus
using namespace arduino;
#endif
1 change: 0 additions & 1 deletion cores/rp2040/SerialPIO.h
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Expand Up @@ -29,7 +29,6 @@ extern "C" typedef struct uart_inst uart_inst_t;

class SerialPIO : public arduino::HardwareSerial {
public:
static const pin_size_t NOPIN = 0xff; // Use in constructor to disable RX or TX unit
SerialPIO(pin_size_t tx, pin_size_t rx, size_t fifoSize = 32);
~SerialPIO();

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4 changes: 2 additions & 2 deletions docs/piouart.rst
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Expand Up @@ -12,13 +12,13 @@ are supported, as well as data sizes from 5- to 8-bits. Fifosize, if not
specified, defaults to 32 bytes.

To instantiate only a serial transmit or receive unit, pass in
``SerialPIO::NOPIN`` as the ``txpin`` or ``rxpin``.
``NOPIN`` as the ``txpin`` or ``rxpin``.

For example, to make a transmit-only port on GP16

.. code:: cpp

SerialPIO transmitter( 16, SerialPIO::NOPIN );
SerialPIO transmitter( 16, NOPIN );

For detailed information about the Serial ports, see the
Arduino `Serial Reference <https://www.arduino.cc/reference/en/language/functions/communication/serial/>`_ .
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3 changes: 3 additions & 0 deletions docs/spi.rst
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Expand Up @@ -16,6 +16,9 @@ SPI pinouts can be set **before SPI.begin()** using the following calls:
Note that the ``CS`` pin can be hardware or software controlled by the sketch.
When software controlled, the ``setCS()`` call is ignored.

Passing in ``NOPIN`` to either ``setRX`` or ``setTX`` will disable SPI on that
interface, making it behave as a unidirectional (output- or input-only SPI interface.

The Arduino `SPI documentation <https://docs.arduino.cc/language-reference/en/functions/communication/SPI/>`_ gives
a detailed overview of the library, except for the following RP2040-specific
changes:
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31 changes: 27 additions & 4 deletions libraries/SPI/src/SPI.cpp
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Expand Up @@ -281,6 +281,11 @@ bool SPIClassRP2040::setRX(pin_size_t pin) {
return true;
}

if (!_running && (pin == NOPIN)) {
_RX = pin;
return true;
}

if (_running) {
panic("FATAL: Attempting to set SPI%s.RX while running", spi_get_index(_spi) ? "1" : "");
} else {
Expand Down Expand Up @@ -362,6 +367,11 @@ bool SPIClassRP2040::setTX(pin_size_t pin) {
return true;
}

if (!_running && (pin == NOPIN)) {
_TX = pin;
return true;
}

if (_running) {
panic("FATAL: Attempting to set SPI%s.TX while running", spi_get_index(_spi) ? "1" : "");
} else {
Expand All @@ -372,13 +382,22 @@ bool SPIClassRP2040::setTX(pin_size_t pin) {

void SPIClassRP2040::begin(bool hwCS) {
DEBUGSPI("SPI::begin(%d), rx=%d, cs=%d, sck=%d, tx=%d\n", hwCS, _RX, _CS, _SCK, _TX);
gpio_set_function(_RX, GPIO_FUNC_SPI);

if ((_RX == NOPIN) && (_TX == NOPIN)) {
panic("SPI%s: TX and RX assigned to NOPIN", spi_get_index(_spi) ? "1" : "");
}

if (_RX != NOPIN) {
gpio_set_function(_RX, GPIO_FUNC_SPI);
}
_hwCS = hwCS;
if (hwCS) {
gpio_set_function(_CS, GPIO_FUNC_SPI);
}
gpio_set_function(_SCK, GPIO_FUNC_SPI);
gpio_set_function(_TX, GPIO_FUNC_SPI);
if (_TX != NOPIN) {
gpio_set_function(_TX, GPIO_FUNC_SPI);
}
// Give a default config in case user doesn't use beginTransaction
beginTransaction(_spis);
endTransaction();
Expand All @@ -391,12 +410,16 @@ void SPIClassRP2040::end() {
_initted = false;
spi_deinit(_spi);
}
gpio_set_function(_RX, GPIO_FUNC_SIO);
if (_RX != NOPIN) {
gpio_set_function(_RX, GPIO_FUNC_SIO);
}
if (_hwCS) {
gpio_set_function(_CS, GPIO_FUNC_SIO);
}
gpio_set_function(_SCK, GPIO_FUNC_SIO);
gpio_set_function(_TX, GPIO_FUNC_SIO);
if (_TX != NOPIN) {
gpio_set_function(_TX, GPIO_FUNC_SIO);
}
_spis = SPISettings(0, LSBFIRST, SPI_MODE0);
}

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100 changes: 50 additions & 50 deletions libraries/SPI/src/SPI.h
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Original file line number Diff line number Diff line change
Expand Up @@ -31,21 +31,21 @@
class SPIClassRP2040 : public arduino::HardwareSPI {
public:
/**
@brief Create a PIO-based SPI instance, pins can be changed before begin() call
@brief Create a PIO-based SPI instance, pins can be changed before begin() call

@param [in] spi SPI hardware instance (spi0/spi1)
@param [in] rx MISO GPIO
@param [in] cs CS GPIO
@param [in] sck SCK GPIO
@param [in] tx MOSI GPIO
@param [in] spi SPI hardware instance (spi0/spi1)
@param [in] rx MISO GPIO
@param [in] cs CS GPIO
@param [in] sck SCK GPIO
@param [in] tx MOSI GPIO
*/
SPIClassRP2040(spi_inst_t *spi, pin_size_t rx, pin_size_t cs, pin_size_t sck, pin_size_t tx);

/**
@brief Send an 8-bit byte of data and return read-back 8-bit value
@brief Send an 8-bit byte of data and return read-back 8-bit value

@param [in] data Data to send
@returns Read back byte from SPI interface
@param [in] data Data to send
@returns Read back byte from SPI interface
*/
byte transfer(uint8_t data) override;

Expand All @@ -67,11 +67,11 @@ class SPIClassRP2040 : public arduino::HardwareSPI {
void transfer(void *buf, size_t count) override;

/**
@brief Sends one buffer and receives into another under a single CS. Can set rx or txbuf to nullptr
@brief Sends one buffer and receives into another under a single CS. Can set rx or txbuf to nullptr

@param [in] txbuf Buffer to transmit or nullptr to send 0s
@param [out] rxbuf Buffer to read back into or nullptr to ignore returned data
@param [in] count Numbner of bytes to transmit/receive
@param [in] txbuf Buffer to transmit or nullptr to send 0s
@param [out] rxbuf Buffer to read back into or nullptr to ignore returned data
@param [in] count Numbner of bytes to transmit/receive
*/
void transfer(const void *txbuf, void *rxbuf, size_t count) override;

Expand Down Expand Up @@ -108,134 +108,134 @@ class SPIClassRP2040 : public arduino::HardwareSPI {


/**
@brief Begin an SPI transaction, sets SPI speed and masks necessary interrupts
@brief Begin an SPI transaction, sets SPI speed and masks necessary interrupts

@param [in] SPISettings SPI configuration parameters, including the clock speed
@param [in] SPISettings SPI configuration parameters, including the clock speed
*/
void beginTransaction(SPISettings settings) override;

/**
@brief Ends an SPI transaction, unmasks and masked GPIO interrupts
@brief Ends an SPI transaction, unmasks and masked GPIO interrupts
*/
void endTransaction(void) override;

/**
@brief Sets the MISO(RX) pin. Call before begin()
@brief Sets the MISO(RX) pin. Call before begin()

@param [in] pin The GPIO number to assign to
@returns True on success
@param [in] pin The GPIO number to assign to or NOPIN
@returns True on success
*/
bool setRX(pin_size_t pin);

/**
@brief Sets the MISO(RX) pin. Call before begin()
@brief Sets the MISO(RX) pin. Call before begin()

@param [in] pin The GPIO number to assign to
@returns True on success
@param [in] pin The GPIO number to assign to
@returns True on success
*/
inline bool setMISO(pin_size_t pin) {
return setRX(pin);
}

/**
@brief Sets the CS pin. Call before begin()
@brief Sets the CS pin. Call before begin()

@param [in] pin The GPIO number to assign to
@returns True on success
@param [in] pin The GPIO number to assign to
@returns True on success
*/
bool setCS(pin_size_t pin);

/**
@brief Sets the SCK pin. Call before begin()
@brief Sets the SCK pin. Call before begin()

@param [in] pin The GPIO number to assign to
@returns True on success
@param [in] pin The GPIO number to assign to
@returns True on success
*/
bool setSCK(pin_size_t pin);

/**
@brief Sets the MOSI(TX) pin. Call before begin()
@brief Sets the MOSI(TX) pin. Call before begin()

@param [in] pin The GPIO number to assign to
@returns True on success
@param [in] pin The GPIO number to assign to
@returns True on success
*/
bool setTX(pin_size_t pin);

/**
@brief Sets the MOSI(TX) pin. Call before begin()
@brief Sets the MOSI(TX) pin. Call before begin()

@param [in] pin The GPIO number to assign to
@returns True on success
@param [in] pin The GPIO number to assign to or NOPIN
@returns True on success
*/
inline bool setMOSI(pin_size_t pin) {
return setTX(pin);
}

/**
@brief Call once to init/deinit SPI class, select pins, etc.
@brief Call once to init/deinit SPI class, select pins, etc.
*/
virtual void begin() override {
begin(false);
}

/**
@brief Call once to init/deinit SPI class, select pins, etc.
@brief Call once to init/deinit SPI class, select pins, etc.

@param [in] hwCS Pass in true to enable HW-controlled CS. Otherwise application needs to assert/deassert CS.
@param [in] hwCS Pass in true to enable HW-controlled CS. Otherwise application needs to assert/deassert CS.
*/
void begin(bool hwCS);

/**
@brief Call to deinit and disable the SPI interface.
@brief Call to deinit and disable the SPI interface.
*/
void end() override;

/**
@brief Deprecated, do not use
@brief Deprecated, do not use

@param [in] order Deprecated
@param [in] order Deprecated
*/
void setBitOrder(BitOrder order) __attribute__((deprecated));

/**
@brief Deprecated, do not use
@brief Deprecated, do not use

@param [in] order Deprecated
@param [in] order Deprecated
*/
void setDataMode(uint8_t uc_mode) __attribute__((deprecated));

/**
@brief Deprecated, do not use
@brief Deprecated, do not use

@param [in] order Deprecated
@param [in] order Deprecated
*/
void setClockDivider(uint8_t uc_div) __attribute__((deprecated));

/**
@brief Ensure specific GPIO interrupt is disabled during and SPI transaction to protect against re-entrancy. Multiple GPIOs supported by multiple calls.
@brief Ensure specific GPIO interrupt is disabled during and SPI transaction to protect against re-entrancy. Multiple GPIOs supported by multiple calls.

@param [in] interruptNumber GPIO pin to mask
@param [in] interruptNumber GPIO pin to mask
*/
virtual void usingInterrupt(int interruptNumber) override {
_helper.usingInterrupt(interruptNumber);
}

/**
@brief Remove a GPIO from the masked-during-transaction list.
@brief Remove a GPIO from the masked-during-transaction list.

@param [in] interruptNumber GPIO pin to unmask
@param [in] interruptNumber GPIO pin to unmask
*/
virtual void notUsingInterrupt(int interruptNumber) override {
_helper.notUsingInterrupt(interruptNumber);
}

/**
@brief Deprecated, do not use
@brief Deprecated, do not use
*/
virtual void attachInterrupt() override __attribute__((deprecated)) { /* noop */ }

/**
@brief Deprecated, do not use
@brief Deprecated, do not use
*/
virtual void detachInterrupt() override __attribute__((deprecated)) { /* noop */ }

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