SPI Module

Since Origin / Contributor Maintainer Source
2015-01-16 Ibrahim Abd Elkader Arnim Läuger spi.c

All transactions for sending and receiving are most-significant-bit first and least-significant last. For technical details of the underlying hardware refer to metalphreak's ESP8266 HSPI articles.

Note

The ESP hardware provides two SPI busses, with IDs 0, and 1, which map to pins generally labelled SPI and HSPI. If you are using any kind of development board which provides flash, then bus ID 0 (SPI) is almost certainly used for communicating with the flash chip. You probably want to choose bus ID 1 (HSPI) for your communication, as you will have uncontended use of it.

HSPI signals are fixed to the following IO indices and GPIO pins:

Signal IO index ESP8266 pin
HSPI CLK 5 GPIO14
HSPI /CS 8 GPIO15
HSPI MOSI 7 GPIO13
HSPI MISO 6 GPIO12

See also spi.setup().

High Level Functions

The high level functions provide a send & receive API for half- and full-duplex mode. Sent and received data items are restricted to 1 - 32 bit length and each data item is surrounded by (H)SPI CS inactive.

spi.recv()

Receive data from SPI.

Syntax

spi.recv(id, size[, default_data])

Parameters

  • id SPI ID number: 0 for SPI, 1 for HSPI
  • size number of data items to be read
  • default_data default data being sent on MOSI (all-1 if omitted)

Returns

String containing the bytes read from SPI.

See also

spi.send()

spi.send()

Send data via SPI in half-duplex mode. Send & receive data in full-duplex mode.

Syntax

HALFDUPLEX:
wrote = spi.send(id, data1[, data2[, ..., datan]])

FULLDUPLEX:
wrote[, rdata1[, ..., rdatan]] = spi.send(id, data1[, data2[, ..., datan]])

Parameters

  • id SPI ID number: 0 for SPI, 1 for HSPI
  • data data can be either a string, a table or an integer number.
    Each data item is considered with databits number of bits.

Returns

  • wrote number of written bytes
  • rdata received data when configured with spi.FULLDUPLEX
    Same data type as corresponding data parameter.

Example

=spi.send(1, 0, 255, 255, 255)
4       255     192     32      0
x = {spi.send(1, 0, 255, 255, 255)}
=x[1]
4
=x[2]
255
=x[3]
192
=x[4]
32
=x[5]
0
=x[6]
nil
=#x
5

_, _, x = spi.send(1, 0, {255, 255, 255})
=x[1]
192
=x[2]
32
=x[3]
0

See also

spi.setup()

Set up the SPI configuration. Refer to Serial Peripheral Interface Bus for details regarding the clock polarity and phase definition.

Calling spi.setup() will route the HSPI signals to the related pins, overriding previous configuration and control by the gpio module. It is possible to revert any pin back to gpio control if its HSPI functionality is not needed, just set the desired gpio.mode() for it. This is recommended especially for the HSPI /CS pin function in case that SPI slave-select is driven from a different pin by gpio.write() - the SPI engine would toggle pin 8 otherwise.

Syntax

spi.setup(id, mode, cpol, cpha, databits, clock_div[, duplex_mode])

Parameters

  • id SPI ID number: 0 for SPI, 1 for HSPI
  • mode select master or slave mode
    • spi.MASTER
    • spi.SLAVE - not supported currently
  • cpol clock polarity selection
    • spi.CPOL_LOW
    • spi.CPOL_HIGH
  • cpha clock phase selection
    • spi.CPHA_LOW
    • spi.CPHA_HIGH
  • databits number of bits per data item 1 - 32
  • clock_div SPI clock divider, f(SPI) = 80 MHz / clock_div, 1 .. n (0 defaults to divider 8)
  • duplex_mode duplex mode
    • spi.HALFDUPLEX (default when omitted)
    • spi.FULLDUPLEX

Returns

Number: 1

Example

spi.setup(1, spi.MASTER, spi.CPOL_LOW, spi.CPHA_LOW, 8, 8)
-- we won't be using the HSPI /CS line, so disable it again
gpio.mode(8, gpio.INPUT, gpio.PULLUP)

Low Level Hardware Functions

The low level functions provide a hardware-centric API for application scenarios that need to excercise more complex SPI transactions. The programming model is built up around the HW send and receive buffers and SPI transactions are initiated with full control over the hardware features.

spi.get_miso()

Extract data items from MISO buffer after spi.transaction().

Syntax

data1[, data2[, ..., datan]] = spi.get_miso(id, offset, bitlen, num)
string = spi.get_miso(id, num)

Parameters

  • id SPI ID number: 0 for SPI, 1 for HSPI
  • offset bit offset into MISO buffer for first data item
  • bitlen bit length of a single data item
  • num number of data items to retrieve

Returns

num data items or string

See also

spi.transaction()

spi.set_mosi()

Insert data items into MOSI buffer for spi.transaction().

Syntax

spi.set_mosi(id, offset, bitlen, data1[, data2[, ..., datan]])
spi.set_mosi(id, string)

Parameters

  • id SPI ID number: 0 for SPI, 1 for HSPI
  • offset bit offset into MOSI buffer for inserting data1 and subsequent items
  • bitlen bit length of data1, data2, ...
  • data data items where bitlen number of bits are considered for the transaction.
  • string send data to be copied into MOSI buffer at offset 0, bit length 8

Returns

nil

See also

spi.transaction()

spi.transaction()

Start an SPI transaction, consisting of up to 5 phases:

  1. Command
  2. Address
  3. MOSI
  4. Dummy
  5. MISO

Syntax

spi.transaction(id, cmd_bitlen, cmd_data, addr_bitlen, addr_data, mosi_bitlen, dummy_bitlen, miso_bitlen)

Parameters

  • id SPI ID number: 0 for SPI, 1 for HSPI
  • cmd_bitlen bit length of the command phase (0 - 16)
  • cmd_data data for command phase
  • addr_bitlen bit length for address phase (0 - 32)
  • addr_data data for command phase
  • mosi_bitlen bit length of the MOSI phase (0 - 512)
  • dummy_bitlen bit length of the dummy phase (0 - 256)
  • miso_bitlen bit length of the MISO phase (0 - 512) for half-duplex.
    Full-duplex mode is activated with a negative value.

Returns

nil

See also