spi(3)

📦

version 1.75 · 5 versions

1.75 · debian trixie, ubuntu noble, ubuntu questing (latest)
26.03 · nixos 26.05, nixpkgs unstable
1.71 · ubuntu jammy
1.71 · debian bookworm
1.75 · ubuntu resolute, ubuntu stonking

, in debian trixie, ubuntu noble, ubuntu questing

💖 spi — SPI access 💖

okay bestie, so this is the spi(3) page from the Library Functions Manual ✨ and it's literally all about making your Raspberry Pi talk to external SPI devices. it's giving hardware-girlie energy, no cap 🦋

🌸 NAME 🌸

spi — SPI access 💅

✨ SYNOPSIS ✨

🎀 Functions 🎀

int bcm2835_spi_begin (void)
void bcm2835_spi_end (void)
void bcm2835_spi_setBitOrder (uint8_t order)
void bcm2835_spi_setClockDivider (uint16_t divider)
void bcm2835_spi_set_speed_hz (uint32_t speed_hz)
void bcm2835_spi_setDataMode (uint8_t mode)
void bcm2835_spi_chipSelect (uint8_t cs)
void bcm2835_spi_setChipSelectPolarity (uint8_t cs, uint8_t active)
uint8_t bcm2835_spi_transfer (uint8_t value)
void bcm2835_spi_transfernb (char *tbuf, char *rbuf, uint32_t len)
void bcm2835_spi_transfern (char *buf, uint32_t len)
void bcm2835_spi_writenb (const char *buf, uint32_t len)
void bcm2835_spi_write (uint16_t data)
int bcm2835_aux_spi_begin (void)
void bcm2835_aux_spi_end (void)
void bcm2835_aux_spi_setClockDivider (uint16_t divider)
uint16_t bcm2835_aux_spi_CalcClockDivider (uint32_t speed_hz)
void bcm2835_aux_spi_write (uint16_t data)
void bcm2835_aux_spi_writenb (const char *buf, uint32_t len)
void bcm2835_aux_spi_transfern (char *buf, uint32_t len)
void bcm2835_aux_spi_transfernb (const char *tbuf, char *rbuf, uint32_t
    len)
uint8_t bcm2835_aux_spi_transfer (uint8_t value)

🦋 Detailed Description 🦋

ok so these functions let you use SPI0 (Serial Peripheral Interface) to interface with an external SPI device. that's the whole vibe. that's the whole point. ✨

💜 Function Documentation 💜

`int bcm2835_aux_spi_begin (void)` [extern]

Starts AUX SPI operations, bestie 💫 it forces the RPi AUX SPI pins P1-38 (MOSI), P1-38 (MISO), P1-40 (CLK) and P1-36 (CE2) to alternate function ALT4, which is what actually enables those pins for the SPI interface.

(yes, the original really does say P1-38 twice up there, i'm just the messenger 🙈)

Returns

1 if successful, 0 otherwise — perhaps because you are not running as root 💀

`uint16_t bcm2835_aux_spi_CalcClockDivider (uint32_t speed_hz)` [extern]

Calculates the input for

See also

bcm2835_aux_spi_setClockDivider

Parameters

speed_hz — A value between

See also

BCM2835_AUX_SPI_CLOCK_MIN and
BCM2835_AUX_SPI_CLOCK_MAX

Returns

Input for

See also

bcm2835_aux_spi_setClockDivider

ngl this section is a lil bit of a cliffhanger, i'm just telling you what it says 💀

`void bcm2835_aux_spi_end (void)` [extern]

Ends AUX SPI operations 🌙 the SPI1 pins P1-38 (MOSI), P1-38 (MISO), P1-40 (CLK) and P1-36 (CE2) get returned to their default INPUT behaviour. so they go back to being regular lil pins 🎀

`void bcm2835_aux_spi_setClockDivider (uint16_t divider)` [extern]

Sets the AUX SPI clock divider, which is basically the same thing as setting the AUX SPI clock speed 🔥

Parameters

divider — The desired AUX SPI clock divider.

`uint8_t bcm2835_aux_spi_transfer (uint8_t value)` [extern]

Transfers one byte to and from the AUX SPI slave ✨ it clocks the 8 bit value out on MOSI, and simultaneously clocks in data from MISO. then it returns the read data byte from the slave. two-way street, main character energy 🫶

Parameters

value — The 8 bit data byte to write to MOSI

Returns

The 8 bit byte simultaneously read from MISO

See also

bcm2835_aux_spi_transfern()

`void bcm2835_aux_spi_transfern (char * buf, uint32_t len)` [extern]

Transfers any number of bytes to and from the AUX SPI slave, using bcm2835_aux_spi_transfernb under the hood. the returned data from the slave replaces the transmitted data in the buffer — so yeah, your buffer gets rewritten, that's the whole trick 💅

Parameters

buf — Buffer of bytes to send. Received bytes will replace the contents
len — Number of bytes in the buffer, and the number of bytes to send/received

See also

bcm2835_aux_spi_transfer()

`void bcm2835_aux_spi_transfernb (const char * tbuf, char * rbuf, uint32_t len)` [extern]

Transfers any number of bytes to and from the AUX SPI slave 💫 it asserts the CE2 pin during the transfer. clocks the len 8 bit bytes out on MOSI, and simultaneously clocks in data from MISO. the data read from the slave gets placed into rbuf.

warning bestie — rbuf must be at least len bytes long or you're gonna have a bad time 😭

Parameters

tbuf — Buffer of bytes to send.
rbuf — Received bytes will by put in this buffer
len — Number of bytes in the tbuf buffer, and the number of bytes to send/received

`void bcm2835_aux_spi_write (uint16_t data)` [extern]

Transfers half-word to the AUX SPI slave 🌸 it asserts the currently selected CS pins during the transfer.

Parameters

data — The 8 bit data byte to write to MOSI

Returns

The 16 bit byte simultaneously read from MISO

See also

bcm2835_spi_transfern()

`void bcm2835_aux_spi_writenb (const char * buf, uint32_t len)` [extern]

Transfers any number of bytes to the AUX SPI slave (no reading back this time, it's a one-way moment 💅). asserts the CE2 pin during the transfer.

Parameters

buf — Buffer of bytes to send.
len — Number of bytes in the tbuf buffer, and the number of bytes to send

`int bcm2835_spi_begin (void)` [extern]

Starts SPI operations, periodt ✨ it forces RPi SPI0 pins P1-19 (MOSI), P1-21 (MISO), P1-23 (CLK), P1-24 (CE0) and P1-26 (CE1) to alternate function ALT0, which enables those pins for the SPI interface.

you should call bcm2835_spi_end() when all SPI functions are complete, so the pins go back to their default functions. clean up after yourself, queen 👑

See also

bcm2835_spi_end()

Returns

1 if successful, 0 otherwise — perhaps because you are not running as root 💀

`void bcm2835_spi_chipSelect (uint8_t cs)` [extern]

Sets the chip select pin(s) 🎀 when a bcm2835_spi_transfer() is made, the selected pin(s) will be asserted during the transfer.

Parameters

cs — Specifies the CS pin(s) that are used to activate the desired slave. One of BCM2835_SPI_CS*, see bcm2835SPIChipSelect

`void bcm2835_spi_end (void)` [extern]

Ends SPI operations 🌙 SPI0 pins P1-19 (MOSI), P1-21 (MISO), P1-23 (CLK), P1-24 (CE0) and P1-26 (CE1) are returned to their default INPUT behaviour.

`void bcm2835_spi_set_speed_hz (uint32_t speed_hz)` [extern]

Sets the SPI clock divider by converting the speed parameter into the equivalent SPI clock divider. ( see

See also

bcm2835_spi_setClockDivider

Parameters

speed_hz — The desired SPI clock speed in Hz

`void bcm2835_spi_setBitOrder (uint8_t order)` [extern]

Sets the SPI bit order 🔁 it sets the bit order used for transmit and receive. the bcm2835 SPI0 only supports BCM2835_SPI_BIT_ORDER_MSB, so if you pick BCM2835_SPI_BIT_ORDER_LSB, the bytes get reversed in software instead. the library defaults to BCM2835_SPI_BIT_ORDER_MSB.

Parameters

order — The desired bit order, one of BCM2835_SPI_BIT_ORDER_*, see bcm2835SPIBitOrder

`void bcm2835_spi_setChipSelectPolarity (uint8_t cs, uint8_t active)` [extern]

Sets the chip select pin polarity for a given pin ✨ when a bcm2835_spi_transfer() occurs, the currently selected chip select pin(s) will be asserted to the value given by active. when transfers are not happening, the chip select pin(s) return to the complement (inactive) value. so it flips back on its own, cute 🎀

Parameters

cs — The chip select pin to affect
active — Whether the chip select pin is to be active HIGH

`void bcm2835_spi_setClockDivider (uint16_t divider)` [extern]

Sets the SPI clock divider, and therefore the SPI clock speed 🔥

Parameters

divider — The desired SPI clock divider, one of BCM2835_SPI_CLOCK_DIVIDER_*, see bcm2835SPIClockDivider

`void bcm2835_spi_setDataMode (uint8_t mode)` [extern]

Sets the SPI data mode — that's the clock polarity and phase 🌈

Parameters

mode — The desired data mode, one of BCM2835_SPI_MODE*, see bcm2835SPIMode

`uint8_t bcm2835_spi_transfer (uint8_t value)` [extern]

Transfers one byte to and from the currently selected SPI slave 💫 it asserts the currently selected CS pins (as previously set by bcm2835_spi_chipSelect) during the transfer. clocks the 8 bit value out on MOSI, and simultaneously clocks in data from MISO. returns the read data byte from the slave. uses polled transfer as per section 10.6.1 of the BCM 2835 ARM Peripherls manual 📖

Parameters

value — The 8 bit data byte to write to MOSI

Returns

The 8 bit byte simultaneously read from MISO

See also

bcm2835_spi_transfern()

`void bcm2835_spi_transfern (char * buf, uint32_t len)` [extern]

Transfers any number of bytes to and from the currently selected SPI slave, using bcm2835_spi_transfernb. the returned data from the slave replaces the transmitted data in the buffer 🫶

Parameters

buf — Buffer of bytes to send. Received bytes will replace the contents
len — Number of bytes in the buffer, and the number of bytes to send/received

See also

bcm2835_spi_transfer()

`void bcm2835_spi_transfernb (char * tbuf, char * rbuf, uint32_t len)` [extern]

Transfers any number of bytes to and from the currently selected SPI slave ✨ it asserts the currently selected CS pins (as previously set by bcm2835_spi_chipSelect) during the transfer. clocks the len 8 bit bytes out on MOSI, and simultaneously clocks in data from MISO. the data read from the slave gets placed into rbuf.

bestie listen — rbuf must be at least len bytes long 😭

uses polled transfer as per section 10.6.1 of the BCM 2835 ARM Peripherls manual 📖

Parameters

tbuf — Buffer of bytes to send.
rbuf — Received bytes will by put in this buffer
len — Number of bytes in the tbuf buffer, and the number of bytes to send/received

See also

bcm2835_spi_transfer()

`void bcm2835_spi_write (uint16_t data)` [extern]

Transfers half-word to the currently selected SPI slave 💅 it asserts the currently selected CS pins (as previously set by bcm2835_spi_chipSelect) during the transfer. clocks the 8 bit value out on MOSI, and simultaneously clocks in data from MISO. uses polled transfer as per section 10.6.1 of the BCM 2835 ARM Peripherls manual 📖

Parameters

data — The 8 bit data byte to write to MOSI

See also

bcm2835_spi_writenb()

`void bcm2835_spi_writenb (const char * buf, uint32_t len)` [extern]

Transfers any number of bytes to the currently selected SPI slave 🌸 it asserts the currently selected CS pins (as previously set by bcm2835_spi_chipSelect) during the transfer.

Parameters

buf — Buffer of bytes to send.
len — Number of bytes in the buf buffer, and the number of bytes to send

👑 Author 👑

Generated automatically by Doxygen for bcm2835 from the source code. the robots wrote this one, not me 💀✨

and that's the whole page bestie, you ate it 💅 this was spi(3) from bcm2835, Version 1.75 🎀 go forth and clock some bits, ily 🫶🌸

📦 where this page comes from

debian trixie: libbcm2835-dev 1.75+ds-1 · GPL-3.0-only
ubuntu noble: libbcm2835-dev 1.75+ds-1 · GPL-3.0-only
ubuntu questing: libbcm2835-dev 1.75+ds-1
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on 2026-10-14: a language model's rewrite of the original, under its terms

spi(3)

💖 spi — SPI access 💖

🌸 NAME 🌸

✨ SYNOPSIS ✨

🎀 Functions 🎀

🦋 Detailed Description 🦋

💜 Function Documentation 💜

int bcm2835_aux_spi_begin (void) [extern]

uint16_t bcm2835_aux_spi_CalcClockDivider (uint32_t speed_hz) [extern]

void bcm2835_aux_spi_end (void) [extern]

void bcm2835_aux_spi_setClockDivider (uint16_t divider) [extern]

uint8_t bcm2835_aux_spi_transfer (uint8_t value) [extern]

void bcm2835_aux_spi_transfern (char * buf, uint32_t len) [extern]

void bcm2835_aux_spi_transfernb (const char * tbuf, char * rbuf, uint32_t len) [extern]

void bcm2835_aux_spi_write (uint16_t data) [extern]

void bcm2835_aux_spi_writenb (const char * buf, uint32_t len) [extern]

int bcm2835_spi_begin (void) [extern]

void bcm2835_spi_chipSelect (uint8_t cs) [extern]

void bcm2835_spi_end (void) [extern]

void bcm2835_spi_set_speed_hz (uint32_t speed_hz) [extern]

void bcm2835_spi_setBitOrder (uint8_t order) [extern]

void bcm2835_spi_setChipSelectPolarity (uint8_t cs, uint8_t active) [extern]

void bcm2835_spi_setClockDivider (uint16_t divider) [extern]

void bcm2835_spi_setDataMode (uint8_t mode) [extern]

uint8_t bcm2835_spi_transfer (uint8_t value) [extern]

void bcm2835_spi_transfern (char * buf, uint32_t len) [extern]

void bcm2835_spi_transfernb (char * tbuf, char * rbuf, uint32_t len) [extern]

void bcm2835_spi_write (uint16_t data) [extern]

void bcm2835_spi_writenb (const char * buf, uint32_t len) [extern]

👑 Author 👑

`int bcm2835_aux_spi_begin (void)` [extern]

`uint16_t bcm2835_aux_spi_CalcClockDivider (uint32_t speed_hz)` [extern]

`void bcm2835_aux_spi_end (void)` [extern]

`void bcm2835_aux_spi_setClockDivider (uint16_t divider)` [extern]

`uint8_t bcm2835_aux_spi_transfer (uint8_t value)` [extern]

`void bcm2835_aux_spi_transfern (char * buf, uint32_t len)` [extern]

`void bcm2835_aux_spi_transfernb (const char * tbuf, char * rbuf, uint32_t len)` [extern]

`void bcm2835_aux_spi_write (uint16_t data)` [extern]

`void bcm2835_aux_spi_writenb (const char * buf, uint32_t len)` [extern]

`int bcm2835_spi_begin (void)` [extern]

`void bcm2835_spi_chipSelect (uint8_t cs)` [extern]

`void bcm2835_spi_end (void)` [extern]

`void bcm2835_spi_set_speed_hz (uint32_t speed_hz)` [extern]

`void bcm2835_spi_setBitOrder (uint8_t order)` [extern]

`void bcm2835_spi_setChipSelectPolarity (uint8_t cs, uint8_t active)` [extern]

`void bcm2835_spi_setClockDivider (uint16_t divider)` [extern]

`void bcm2835_spi_setDataMode (uint8_t mode)` [extern]

`uint8_t bcm2835_spi_transfer (uint8_t value)` [extern]

`void bcm2835_spi_transfern (char * buf, uint32_t len)` [extern]

`void bcm2835_spi_transfernb (char * tbuf, char * rbuf, uint32_t len)` [extern]

`void bcm2835_spi_write (uint16_t data)` [extern]

`void bcm2835_spi_writenb (const char * buf, uint32_t len)` [extern]