nuttx-apps/system/spi/README.md

# System / `spi` SPI Tool

The I2C tool provides a way to debug SPI related problems. This README file will
provide usage information for the SPI tools.

## Contents

- System Requirements
  - SPI Driver
  - Configuration Options
- Help
- Common Line Form
- Common Command Options
  - _Sticky_ Options
  - Environment variables
  - Common Option Summary
- Command summary
  - `bus`
  - `dev`
  - `get`
  - `set`
  - `verf`
- I2C Build Configuration
  - NuttX Configuration Requirements
  - I2C Tool Configuration Options

## System Requirements

The SPI tool is designed to be implemented as a NuttShell (NSH) add-on. Read the
`apps/nshlib/README.md` file for information about add-ons.

### Configuration Options

- `CONFIG_NSH_BUILTIN_APPS` – Build the tools as an NSH built-in command.
- `CONFIG_SPITOOL_MINBUS`   – Smallest bus index supported by the hardware
  (default `0`).
- `CONFIG_SPITOOL_MAXBUS`   – Largest bus index supported by the hardware
  (default `3`).
- `CONFIG_SPITOOL_DEFFREQ`  – Default frequency (default: `40000000`).
- `CONFIG_SPITOOL_DEFMODE`  – Default mode, where
  ```
  0 = CPOL=0, CPHA=0
  1 = CPOL=0, CPHA=1
  2 = CPOL=1, CPHA=0
  3 = CPOL=1, CPHA=1
  ```
- `CONFIG_SPITOOL_DEFWIDTH` – Default bit width (default `8`).
- `CONFIG_SPITOOL_DEFWORDS` – Default number of words to exchange (default `1`).

## Help

The SPI tools supports some help output. That help output can be view by
entering either:

```
nsh> spi help
```

or

```
nsh> spi ?
```

Here is an example of the help output. I shows the general form of the command
line, the various SPI commands supported with their unique command line options,
and a more detailed summary of the command SPI command options.

```
nsh> Usage: spi <cmd> [arguments]

Where <cmd> is one of:

  Show help     : ?
  List buses    : bus
  SPI Exchange  : exch [OPTIONS] [<hex senddata>]
  Show help     : help

Where common _sticky_ OPTIONS include:
  [-b bus] is the SPI bus number (decimal).  Default: 0 Current: 2
      [-f freq] SPI frequency.  Default: 4000000 Current: 4000000
  [-m mode] Mode for transfer.  Default: 0 Current: 0
  [-u udelay] Delay after transfer in uS.  Default: 0 Current: 0
  [-w width] Width of bus.  Default: 8 Current: 8
  [-x count] Words to exchange.  Default: 1 Current: 4
```

**Notes**:

- An environment variable like $PATH may be used for any argument.
- Arguments are _sticky_. For example, once the SPI address is specified, that
  address will be re-used until it is changed.

**Warning**:

- The SPI commands may have bad side effects on your SPI devices. Use only at
  your own risk.

## Command Line Form

The SPI is started from NSH by invoking the `spi` command from the NSH command
line. The general form of the `spi` command is:

```shell
spi <cmd> [arguments]
```

Where `<cmd>` is a _sub-command_ and identifies one SPI operation supported by
the tool. `[arguments]` represents the list of arguments needed to perform the
SPI operation. Those arguments vary from command to command as described below.
However, there is also a core set of common `OPTIONS` supported by all commands.
So perhaps a better representation of the general SPI command would be:

```shell
i2c <cmd> [OPTIONS] [arguments]
```

Where `[OPTIONS]` represents the common options and and arguments represent the
operation-specific arguments.

## Common Command Options

### _Sticky_ Options

In order to interact with SPI devices, there are a number of SPI parameters that
must be set correctly. One way to do this would be to provide to set the value
of each separate command for each SPI parameter. The SPI tool takes a different
approach, instead: The SPI configuration can be specified as a (potentially
long) sequence of command line arguments.

These arguments, however, are _sticky_. They are sticky in the sense that once
you set the SPI parameter, that value will remain until it is reset with a new
value (or until you reset the board).

### Environment Variables

**Note** also that if environment variables are not disabled (by
`CONFIG_DISABLE_ENVIRON=y`), then these options may also be environment
variables. Environment variables must be preceded with the special character
`$`. For example, `PWD` is the variable that holds the current working directory
and so `$PWD` could be used as a command line argument. The use of environment
variables on the I2C tools command is really only useful if you wish to write
NSH scripts to execute a longer, more complex series of SPI commands.

### Common Option Summary

- `[-b bus]` is the SPI bus number (decimal). Default: `0`

  Which SPI bus to commiuncate on. The bus must have been initialised as a
  character device in the config in the form `/dev/spiX` (e.g. `/dev/spi2`).

  The valid range of bus numbers is controlled by the configuration settings
  `CONFIG_SPITOOL_MINBUS` and `CONFIG_SPITOOL_MAXBUS`.

  The bus numbers are small, decimal numbers.

- `[-m mode]` SPI Mode for transfer.

  Which of the available SPI modes is to be used. Options are;

  ```
  0 = CPOL=0, CPHA=0
  1 = CPOL=0, CPHA=1
  2 = CPOL=1, CPHA=0
  3 = CPOL=1, CPHA=1
  ```

- `[-u udelay]` Delay after transfer in uS. Default: `0`

  Any extra delay to be provided after the transfer. Not normally needed from
  the command line.

- `[-x count]` Words to exchange  Default: `1`

  The number of words to be transited over the bus. For sanitys sake this is
  limited to a relatively small number (`40` by default). Any data on the
  command line is sent first, padded by `0xFF`'s while any remaining data are
  received.

- `[-w width]` is the data width (varies according to target). Default: `8`

  Various SPI devices support different data widths. This option is untested.

- `[-f freq]` I2C frequency. Default: `4000000` Current: `4000000`

  The `[-f freq]` sets the frequency of the SPI device. The default is very
  conservative.

## Command Summary

### List buses: `bus [OPTIONS]`

This command will simply list all of the configured SPI buses and indicate which
are supported by the driver and which are not:

```
BUS   EXISTS?
Bus 1: YES
Bus 2: NO
```

The valid range of bus numbers is controlled by the configuration settings
`CONFIG_SPITOOL_MINBUS` and `CONFIG_SPITOOL_MAXBUS`.

### Exchange data: `exch [OPTIONS] <Optional TX Data>`

This command triggers an SPI transfer, returning the data back from the far end.
As an example (with MOSI looped back to MISO);

```shell
nsh> spi exch -b 2 -x 4 aabbccdd
```

```
Received: AA BB CC DD
```

Note that the `TX Data` are always specified in hex, and are always two digits
each, case insensitive.

## I2C Build Configuration

### NuttX Configuration Requirements

The SPI tools requires the following in your NuttX configuration:

1. Application configuration.

   Using `make menuconfig`, select the SPI tool. The following definition should
   appear in your `.config` file:

   ```conf
   CONFIG_SYSTEM_SPI=y
   ```

2. Device-specific SPI driver support must be enabled:

   ```conf
   CONFIG_SPI_DRIVER=y
   ```

   The SPI tool will then use the SPI character driver to access the SPI bus.
   These devices will reside at `/dev/spiN` where `N` is the I2C bus number.

   **Note**: The SPI driver `ioctl` interface is defined in
   `include/nuttx/spi/spi.h`.