Our #NuttX Demo App "spi_test" ... Runs OK on #BL602

https://github.com/lupyuen/incubator-nuttx-apps/blob/newapp/examples/spi_test/spi_test_main.c

#NuttX SPI Interface is defined here ... Let's call it from our "spi_test" app

https://github.com/apache/incubator-nuttx/blob/master/include/nuttx/spi/spi.h

Build, Flash and Run #NuttX OS on #BL602 ... Here's the script I use for macOS

https://gist.github.com/lupyuen/cc21385ecc66b5c02d15affd776a64af

Can our #NuttX App directly call the SPI Interface? Let's find out! 🤔

https://github.com/lupyuen/incubator-nuttx-apps/blob/spi_test/examples/spi_test/spi_test_main.c

#NuttX SPI Interface needs an SPI Device "spi_dev_s" ... How do we get an SPI Device? 🤔

https://github.com/lupyuen/incubator-nuttx/blob/master/arch/risc-v/src/bl602/bl602_spi.c#L932-L967

Tracing thru #NuttX Virtual File System ... We see that ioctl() maps the File Descriptor to a File Struct

https://github.com/lupyuen/incubator-nuttx/blob/master/fs/vfs/fs_ioctl.c#L118-L138

#NuttX File Struct contains a Private Pointer to the SPI Driver "spi_driver_s"

https://github.com/lupyuen/incubator-nuttx/blob/master/drivers/spi/spi_driver.c#L112-L147

#NuttX SPI Driver "spi_driver_s" contains the SPI Device "spi_dev_s" ... That we need for testing the SPI Interface! But the SPI Device is private and hidden from apps 🙁

https://github.com/lupyuen/incubator-nuttx/blob/master/drivers/spi/spi_driver.c#L55-L65

Instead we copy an existing #NuttX SPI Device Driver to test the SPI Interface ... We pick the simplest smallest SPI Device Driver: dat-31r5-sp

https://docs.google.com/spreadsheets/d/1MDps5cPe7tIgCL1Cz98iVccJAUJq1lgctpKgg9OwztI/edit#gid=0

We create a new #NuttX SPI Device Driver ... By copying "dat-31r5-sp.c" to "spi_test_driver.c"

https://github.com/lupyuen/incubator-nuttx/blob/newdriver/drivers/rf/spi_test_driver.c

In our SPI Test Driver: Change all "dat31r5sp" to "spi_test_driver" ... Remember to Preserve Case!

https://github.com/lupyuen/incubator-nuttx/commit/8fee69215163180b77dc9d5b9e7449ebe00ac1cc

Do the same to create the Header File for our #NuttX Driver: spi_test_driver.h

https://github.com/lupyuen/incubator-nuttx/blob/newdriver/include/nuttx/rf/spi_test_driver.h

At #NuttX Startup, register our SPI Test Driver as "/dev/spitest0"

https://github.com/lupyuen/incubator-nuttx/blob/newdriver/boards/risc-v/bl602/bl602evb/src/bl602_bringup.c#L599-L617

Add our SPI Test Driver to #NuttX Kconfig

https://github.com/lupyuen/incubator-nuttx/blob/newdriver/drivers/rf/Kconfig#L22-L27

Our SPI Test Driver for #NuttX appears in "make menuconfig"!

https://github.com/lupyuen/incubator-nuttx/blob/newdriver/drivers/rf/Kconfig#L22-L27

Remember to enable "SPI0" and "SPI Character Driver" in #NuttX ... Or our SPI Test Driver won't start

https://github.com/lupyuen/incubator-nuttx/blob/newdriver/drivers/rf/spi_test_driver.c

Here's what happens when we make a boo-boo and #NuttX won't start

https://gist.github.com/lupyuen/ccfd90125f9a180b4cfb459e8a57b323

Update the Makefile "Make.defs" ... So that #NuttX will build our SPI Test Driver

https://github.com/lupyuen/incubator-nuttx/blob/newdriver/drivers/rf/Make.defs#L33-L37