Add preliminary SPI support for BeagleBone Black

[pdp7]

FYI - THIS IS WORK IN PROGRESS. ADDITIONAL COMMITS WILL BE ADDED TO THIS PR.

Refer to header default pin modes
http://beagleboard.org/static/images/cape-headers.png

P9_17 (SPI0_CSO => CE0) enables peripheral device
P9_18 (SPI0_D1 => MOSI) outputs data to peripheral device
P9_21 (SPIO_DO => MISO) receives data from peripheral device
P9_22 (SPI0_SCLK => SCLK) outputs clock signal

Use config-pin to set pin mode for SPI pins
https://github.com/beagleboard/bb.org-overlays/tree/master/tools/beaglebone-universal-io

config-pin p9.17 spi_cs
config-pin p9.18 spi
config-pin p9.21 spi
config-pin p9.22 spi_sclk

[pdp7]

I have wired up the BME280 per the learning guide.

BME280  CS: BBB CE0  / P9_17
BME280 SDI: BBB MOSI / P9_18
BME280 SDO: BBB MISO / P9_21
BME280 SCK: BBB SCLK / P9_22

The BME280 CircuitPython example runs OK on the BeagleBone:

debian@beaglebone:~/Adafruit_CircuitPython_BME280$ sudo python3 examples/bme280_simpletest.py 
SPI(): __init()
SPI(): beaglebone_black: from adafruit_blinka.microcontroller.raspi_23.spi import SPI as _SPI
spiPorts: ((0, P9_22, P9_18, P9_21), (1, P9_22, P9_18, P9_21))
for:
0 P9_22 P9_18 P9_21
Line 91
<class 'adafruit_blinka.microcontroller.raspi_23.spi.SPI'>
<adafruit_blinka.microcontroller.raspi_23.spi.SPI object at 0xb6ac2890>

Temperature: 20.8 C
Humidity: 34.3 %
Pressure: 1006.9 hPa
Altitude = 53.01 meters

Temperature: 20.8 C
Humidity: 34.3 %
Pressure: 1006.9 hPa
Altitude = 52.79 meters

[pdp7]

Testing with SP1 port instead of SPI0

Refer to:
http://beagleboard.org/static/images/cape-headers-spi.png

CE1 P9.28 SPI1_CS0
MISO_1 P9.29 SPI1_D0
MOSI_1 P9.30 SPI1_D1
SCLK_1 P9.31 SPI_SCLK

SPI1 conflicts with HDMI Audio (McASP)

Refer to:
https://elinux.org/Beagleboard:BeagleBoneBlack_Debian#U-Boot_Overlays

To Disable HDMI AUDIO, uncomment this line in /boot/uEnv.txt:

disable_uboot_overlay_audio=1

Set pin modes for SPI1 with:

config-pin p9.28 spi_cs
config-pin p9.29 spi
config-pin p9.30 spi
config-pin p9.31 spi_sclk

BME280 wiring:

BME280  CS:    CE1 P9.28 SPI1_CS0
BME280 SDO: MISO_1 P9.29 SPI1_D0
BME280 SDI: MOSI_1 P9.30 SPI1_D1
BME280 SCK: SCLK_1 P9.31 SPI_SCLK

+++ b/examples/bme280_simpletest.py
@@ -3,15 +3,17 @@ import time
 import board
 import busio
 import adafruit_bme280
+import digitalio
 
 # Create library object using our Bus I2C port
-i2c = busio.I2C(board.SCL, board.SDA)
-bme280 = adafruit_bme280.Adafruit_BME280_I2C(i2c)
+#i2c = busio.I2C(board.SCL, board.SDA)
+#bme280 = adafruit_bme280.Adafruit_BME280_I2C(i2c)
 
 # OR create library object using our Bus SPI port
 #spi = busio.SPI(board.SCK, board.MOSI, board.MISO)
-#bme_cs = digitalio.DigitalInOut(board.D10)
-#bme280 = adafruit_bme280.Adafruit_BME280_SPI(spi, bme_cs)
+spi = busio.SPI(board.SCK_1, board.MOSI_1, board.MISO_1)
+bme_cs = digitalio.DigitalInOut(board.CE1)
+bme280 = adafruit_bme280.Adafruit_BME280_SPI(spi, bme_cs)
 
 # change this to match the location's pressure (hPa) at sea level
 bme280.sea_level_pressure = 1013.25

BME280 on SPI1 works OK

debian@beaglebone:~/Adafruit_CircuitPython_BME280$ sudo python3 ./examples/bme280_simpletest.py 
SPI(): __init()
SPI(): beaglebone_black: from adafruit_blinka.microcontroller.raspi_23.spi import SPI as _SPI
spiPorts: ((0, P9_22, P9_18, P9_21), (1, P9_31, P9_29, P9_30))
for:
0 P9_22 P9_18 P9_21
1 P9_31 P9_29 P9_30
Line 91
<class 'adafruit_blinka.microcontroller.raspi_23.spi.SPI'>
<adafruit_blinka.microcontroller.raspi_23.spi.SPI object at 0xb6b1b890>

Temperature: 22.4 C
Humidity: 34.2 %
Pressure: 1006.7 hPa
Altitude = 54.83 meters

Temperature: 22.4 C
Humidity: 34.1 %
Pressure: 1006.7 hPa
Altitude = 54.80 meters

[pdp7]

@ladyada I have tested OK with both SPI0 and SPI1 on the BeagleBone Black with the BME280 sensor

[ladyada]

rad! ok wanna do a merge and release then?

[pdp7]

@ladyada
yes, that sounds good. merging now