In order to get started with using SPI on the Edison, I have wired up one of Adafruit's OLED boards (Monochrome 128x32 SPI OLED graphic display ID: 661 - $17.50 : Adafruit Industries, Unique & fun DIY electronics and kits) to my edison on the Intel Arduino breakout board.
I am using the linux 64 bit weekly 68 SDK (http://downloadmirror.intel.com/24271/eng/edison-sdk-linux64-weekly-68.zip)
I am using http://downloadmirror.intel.com/24271/eng/arduino-linux64-1.0.3.tgz for my IDE.
I have attached a log of my boot sequence output; it shows what versions of the kernel, etc I am using. I am just using the Yocto image from http://downloadmirror.intel.com/24271/eng/edison-image-ww36-14.zip.
I started with Adafruit's arduino sample code for the oled (adafruit/Adafruit_SSD1306 · GitHub) and Adafruit_SSD1306/ssd1306_128x32_spi.ino at master · adafruit/Adafruit_SSD1306 · GitHub.
Depending on which Adafruit_SSD1306 constructor is used, one can choose from software SPI (where CLK and MOSI are twiddled as GPIOs) or hardware SPI (where the Arduino SPI object is used).
When I use the software SPI constructor, all is good. Basically, this version just uses pins 13 (clk), 11 (mosi), 10 (slave select), plus a couple of oled-specific lines as gpios.
When I use the hardware SPI constructor, I have no success.
In the process of debugging my problem I have determined that the current version of arduino-1.5.3-Intel.1.0.3//hardware/arduino/edison/variants/edison_fab_c/variants.cpp has problems in the mux structures with respect to SPI.
First of all, MuxDesc13's entry for the SPI MODE gpio is:
{ 109, PIN_MODE_1, FN_GPIO }, // SPI mode |
instead of
| { 109, PIN_MODE_1, FN_SPI }, // SPI mode |
Next, g_APinDescription[] does not contain any entries for the GPIOs (109, 114, 115) referenced in MuxDesc11, MuxDesc12, and MuxDesc13.
I fixed these issues in my local version of variant.cpp, and that still did not get hardware SPI working.
I am watching pins 13, 11, and 10 (with LEDs) to see if they ever go high when I run my oled sketch mentioned above, and I see that the clk (13) does go high, the slave select seems to be working, but that's just a plain old gpio, and most importantly, pin 11 (mosi) never goes high, indicating no data is being sent over the wire.
By the way, with the same hardware configuration, if I switch to "software spi" and just use pins 13 and 11 as gpio pins, I see these pins go high as expected.
So my question is, has anybody gotten hardware spi working on the Edison using the Arduino breakout board?
If so, how?