.\"	$NetBSD: spi.9,v 1.2 2019/02/23 17:37:10 wiz Exp $
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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
.In 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.
.Pp
The
.Fa struct spi_handle
corresponding to the device is passed in the driver attachment.
.Bl -tag -width spi_transfer_init
.It Fn spi_configure "sh" "mode" "speed"
Sets mode and speed for subsequent communication with a SPI slave.
.It Fn spi_transfer "sh" "st"
Queue transfer to SPI controller.
.Fn spi_transfer
returns an errno value when the transfer couldn't be queued.
.It Fn spi_transfer_init "st"
Initialize a transfer structure.
.It 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.
.It Fn spi_transfer_add "st" "chunk"
Append a chunk to transfer structure.
.It 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.
.It Fn spi_done "st" "err"
Called back machine-dependent backend to signal completion
of a transfer.
.El
.Pp
For simplicity there are convenience functions that combine
common operations.
These functions return an errno value when the transfer failed.
.Bl -tag -width spi_transfer_init
.It Fn spi_recv "sh" "cnt" "data"
Prepares a chunk for receiving data, queues a transfer and
waits for it to complete.
.It Fn spi_send "sh" "cnt" "data"
Prepares a chunk for sending data, queues a transfer and
waits for it to complete.
.It 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 .