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Written by Michael van Elst
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.Dd February 23, 2019 .Dt SPI 9 .Os .Sh NAME .Nm spi_configure , .Nm spi_transfer , .Nm spi_transfer_init , .Nm spi_chunk_init , .Nm spi_transfer_add , .Nm spi_wait , .Nm spi_done , .Nm spi_send , .Nm spi_recv , .Nm spi_send_recv .Nd Serial Peripheral Interface (SPI) kernel interface .Sh SYNOPSIS n dev/spi/spivar.h .Ft int .Fo spi_configure .Fa "struct spi_handle *sh" .Fa "int mode" .Fa "int speed" .Fc .Ft int .Fo spi_transfer .Fa "struct spi_handle *sh" .Fa "struct spi_transfer *st" .Fc .Ft void .Fo spi_transfer_init .Fa "struct spi_transfer *st" .Fc .Ft void .Fo spi_chunk_init .Fa "struct spi_chunk *chunk" .Fa "int cnt" .Fa "const uint8_t *wptr" .Fa "uint8_t *rptr" .Fc .Ft void .Fo spi_transfer_add .Fa "struct spi_transfer *st" .Fa "struct spi_chunk *chunk" .Fc .Ft void .Fo spi_wait .Fa "struct spi_transfer *st" .Fc .Ft void .Fo spi_done .Fa "struct spi_transfer *st" .Fa "int err" .Fc .Ft int .Fo spi_recv .Fa "struct spi_handle *sh" .Fa "int cnt" .Fa "uint8_t *data" .Fc .Ft int .Fo spi_send .Fa "struct spi_handle *sh" .Fa "int cnt" .Fa "const uint8_t *data" .Fc .Ft int .Fo spi_send_recv .Fa "struct spi_handle *sh" .Fa "int scnt" .Fa "const uint8_t *snd" .Fa "int rcnt" .Fa "const uint8_t *rcv" .Fc .Sh DESCRIPTION SPI is a 4-wire synchronous full-duplex serial bus. It is commonly used for connecting devices such as EEPROMs, displays, and other types of integrated circuits. The .Nm spi interface provides a means of communicating with SPI-connected devices. .Sh FUNCTIONS The following functions comprise the API provided to drivers of SPI-connected devices.
p The .Fa struct spi_handle corresponding to the device is passed in the driver attachment. l -tag -width spi_transfer_init t Fn spi_configure "sh" "mode" "speed" Sets mode and speed for subsequent communication with a SPI slave. t Fn spi_transfer "sh" "st" Queue transfer to SPI controller. .Fn spi_transfer returns an errno value when the transfer couldn't be queued. t Fn spi_transfer_init "st" Initialize a transfer structure. t Fn spi_chunk_init "chunk" "cnt" "wptr" rptr" Initialize a chunk structure, each chunk corresponds to a possibly bi-directional transfer where the same amount of bytes is shifted in and out. t Fn spi_transfer_add "st" "chunk" Append a chunk to transfer structure. t Fn spi_wait "st" Wait for a transfer to complete. When the transfer has failed for some reason, the field .Va st->st_errno is set to a non-zero value. t Fn spi_done "st" "err" Called back machine-dependent backend to signal completion of a transfer. .El
p For simplicity there are convenience functions that combine common operations. These functions return an errno value when the transfer failed. l -tag -width spi_transfer_init t Fn spi_recv "sh" "cnt" "data" Prepares a chunk for receiving data, queues a transfer and waits for it to complete. t Fn spi_send "sh" "cnt" "data" Prepares a chunk for sending data, queues a transfer and waits for it to complete. t Fn spi_send_recv "sh" "scnt" "snd" "rcnt" "rcv" Prepares two chunks for sending data first and then receiving an answer, queues a transfer and waits for it to complete. This is not a full-duplex operation. .El .Sh SEE ALSO .Xr spi 4 .Sh HISTORY The .Nm spi API first appeared in .Nx 4.0 .
Indexes created Sat Sep 20 22:09:52 GMT 2025