Here's how we configure the #NuttX SPI Interface

https://github.com/lupyuen/incubator-nuttx/blob/spi_test/drivers/rf/spi_test_driver.c#L95-L117

To watch what happens inside #NuttX's SPI Driver for #BL602 ... Turn on SPI Debug Logging

https://github.com/lupyuen/incubator-nuttx/blob/spi_test/arch/risc-v/src/bl602/bl602_spi.c

Now we see every byte transferred by #NuttX's SPI Driver for #BL602!

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

How to verify the #NuttX SPI Output? We sniff the #BL602 SPI Bus with a Logic Analyser

https://lupyuen.github.io/articles/spi#appendix-troubleshoot-bl602-spi-with-logic-analyser

In #NuttX the SPI Pins for #BL602 are defined in "board.h" ... MOSI is GPIO 1, MISO is GPIO 0

https://github.com/lupyuen/incubator-nuttx/blob/spi_test/boards/risc-v/bl602/bl602evb/include/board.h#L87-L92

#NuttX's SPI Pins match the #BL602 Reference Manual: MOSI = GPIO 1, MISO = GPIO 0 ... But we're about to witness a BL602 SPI Quirk

https://github.com/bouffalolab/bl_docs/tree/main/BL602_RM/en

Logic Analyser connected to #BL602 shows that MISO and MOSI are swapped! This happens in BL602 IoT SDK ... Also in #NuttX!

https://lupyuen.github.io/articles/spi#spi-data-pins-are-flipped

We can swap MISO and MOSI on #BL602 by setting a Hardware Register ... Let's do this on #NuttX

https://lupyuen.github.io/articles/pinedio#spi-pins-are-swapped

Here's how we swap #BL602 MOSI and MISO on #NuttX ... So that the SPI Pins are consistent with the BL602 Reference Manual

https://github.com/lupyuen/incubator-nuttx/blob/swap_miso_mosi/arch/risc-v/src/bl602/bl602_spi.c#L1080-L1140

After swapping #BL602 MISO and MOSI at #NuttX startup ... Logic Analyser shows that the SPI Pins are now consistent with BL602 Reference Manual! 🎉

https://github.com/lupyuen/incubator-nuttx/blob/swap_miso_mosi/arch/risc-v/src/bl602/bl602_spi.c#L1080-L1140

Let's test #NuttX SPI with #BL602 and Semtech SX1262 LoRa Transceiver

https://www.semtech.com/products/wireless-rf/lora-core/sx1262

We implement the Read Operation for our #NuttX SPI Driver ... So that we can fetch the SPI Response from SX1262

https://github.com/lupyuen/incubator-nuttx/blob/spi_test/drivers/rf/spi_test_driver.c#L210-L233

Our #NuttX App transmits an SPI Command to SX1262 ... And reads the SPI Response from SX1262

https://github.com/lupyuen/incubator-nuttx-apps/blob/spi_test/examples/spi_test2/spi_test2_main.c#L54-L84

#BL602 SPI Chip Select has a problem ... It goes High after EVERY byte ... Which is no-no for SX1262 ... Solution: We control Chip Select via GPIO

https://github.com/lupyuen/incubator-nuttx-apps/blob/spi_test/examples/spi_test2/spi_test2_main.c#L42-L74

Here's our #NuttX App controlling SPI Chip Select via GPIO

https://github.com/lupyuen/incubator-nuttx-apps/blob/spi_test/examples/spi_test2/spi_test2_main.c#L42-L74

Now our #NuttX App is ready to read an SX1262 Register over SPI!

https://github.com/lupyuen/incubator-nuttx-apps/blob/spi_test/examples/spi_test2/spi_test2_main.c#L90-L119

Our #NuttX App reads an SX1262 Register ... But it returns garbage! There's a workaround for this #BL602 SPI Quirk

https://github.com/lupyuen/incubator-nuttx-apps/blob/spi_test/examples/spi_test2/spi_test2_main.c#L90-L119

#BL602 has an SPI Quirk ... We must use SPI Mode 1 instead of Mode 0 ... Let's fix this in #NuttX

https://lupyuen.github.io/articles/spi#spi-phase-looks-sus

For #NuttX on #BL602, we use SPI Mode 1 instead of Mode 0 ... To work around the SPI Mode Quirk

https://github.com/lupyuen/incubator-nuttx/blob/spi_test/drivers/rf/spi_test_driver.c#L51-L57

Our #NuttX App now reads the SX1262 Register correctly! 🎉

https://github.com/lupyuen/incubator-nuttx-apps/blob/spi_test/examples/spi_test2/spi_test2_main.c

Will #NuttX run on #Pine64's PineDio Stack BL604 with onboard Semtech SX1262? Let's find out!

https://lupyuen.github.io/articles/pinedio

Here's how Semtech SX1262 is wired onboard #PineDio Stack #BL604 ... Let's update the Pin Definitions in NuttX

Here are the #NuttX Pin Definitions for PineDio Stack BL604 with onboard SX1262 ... As derived from the schematic

https://github.com/lupyuen/incubator-nuttx/blob/pinedio/boards/risc-v/bl602/bl602evb/include/board.h#L42-L95

Our #NuttX App runs OK on PineDio Stack BL604 with onboard SX1262! 🎉

https://github.com/lupyuen/incubator-nuttx-apps/blob/spi_test/examples/spi_test2/spi_test2_main.c

How we transmit and receive data over SPI on Apache #NuttX OS ... And what's inside the SPI Driver ... All shall be explained here

https://lupyuen.github.io/articles/spi2?1

Calling the SPI Driver in Apache #NuttX OS

https://lupyuen.github.io/articles/spi2?2

To test the #NuttX SPI Functions, we create an App and a Device Driver

https://lupyuen.github.io/articles/spi2?3#spi-test-app-and-driver

#NuttX Apps can't call the SPI Driver directly ... Here's why

https://lupyuen.github.io/articles/spi2?3#spi-test-app-and-driver

Here's how we create a #NuttX App

https://lupyuen.github.io/articles/spi2?4#appendix-create-a-nuttx-app

How we create a Device Driver in #NuttX ... The copy-n-paste way

https://lupyuen.github.io/articles/spi2?5#appendix-create-a-nuttx-device-driver

Enabling the SPI Driver in #NuttX

https://lupyuen.github.io/articles/spi2?6#enable-spi

We enable SPI Logging in #NuttX ... For easier troubleshooting

https://lupyuen.github.io/articles/spi2?7#enable-logging

During #NuttX Startup, we register our Device Driver

https://lupyuen.github.io/articles/spi2?8#register-device-driver

Our Custom Device Driver appears as "/dev/spitest0" in #NuttX

https://lupyuen.github.io/articles/spi2?9#verify-device-driver

Why we chose to clone the "dat-31r5-sp" driver in #NuttX ... Yep we did a Quantitative Analysis of NuttX Drivers!

https://lupyuen.github.io/articles/spi2?10#verify-device-driver

What's inside our SPI Test Driver for #NuttX

https://lupyuen.github.io/articles/spi2?11#inside-the-spi-test-driver

Every #NuttX Device Driver defines a list of File Operations ... Here are the operations for our SPI Test Driver

https://lupyuen.github.io/articles/spi2?12#file-operations

Here's how we transfer data over SPI in #NuttX

https://lupyuen.github.io/articles/spi2?15#write-operation