{"id":223,"date":"2015-01-03T00:25:40","date_gmt":"2015-01-03T00:25:40","guid":{"rendered":"http:\/\/int03.co.uk\/blog\/?page_id=223"},"modified":"2020-11-16T14:58:48","modified_gmt":"2020-11-16T14:58:48","slug":"raspberry-pi-espresso-cpu-from-scratch","status":"publish","type":"page","link":"https:\/\/int03.co.uk\/blog\/raspberry-pi-espresso-cpu-from-scratch\/","title":{"rendered":"Raspberry Pi Espresso CPU… from scratch"},"content":{"rendered":"

Having corrupted my SD card again<\/strong> (deep sigh), it’s time for a complete rebuild again<\/strong>. I thought this would be an opportunity to update these notes.<\/p>\n

The first task is to download an image and write to an SD card. Previously\u00a0I downloaded Raspbian (Kernel 3.12, Release 2014-12-24) from raspberrypi.org<\/a>. I used Win32DiskImager<\/a> to write this to an 8GB SD card. This time I used the Noobs image and selected Raspian OS (although, having done this, I would not recommend Noobs because the two stage boot makes things rather more difficult to set up. If you are starting from scratch,\u00a0I would recommend\u00a0using\u00a0the vanilla Raspbian image as I did originally).<\/p>\n

I’m using a Raspberry Pi Model A, 2nd revision board. After hooking it up to a TV with HDMI, I connected a USB keyboard and wireless USB dongle to the single USB port on the Pi, and powered on.<\/p>\n

First time I did this, the Pi booted up with a configuration menu. I expanded the file-system to fill the SD card, over-clocked to 900Mhz, changed the root password and host-name. More recently, using Noobs, I was able to do this\u00a0same\u00a0configuration under X windows.<\/p>\n

The Pi was set to boot to CLI, without automatic log on, both SPI and I2C were enabled in the configuration.<\/p>\n

The next step is to configure wireless networking. I’m using an Edimax USB adapter (EW-7811Un) apparently based on Realtek RTL8188CUS chipset.<\/p>\n

The contents of\u00a0\/etc\/network\/interfaces<\/strong> were left with the Raspbian defaults. However, the settings in \/etc\/wpa_supplicant\/wpa_supplicant.conf<\/strong>\u00a0needed to be changed to suit my own network, as shown below:<\/p>\n

ctrl_interface=DIR=\/var\/run\/wpa_supplicant GROUP=netdev\nupdate_config=1\n\nnetwork={\n\u00a0\u00a0 \u00a0scan_ssid=1<\/strong>\n\u00a0\u00a0 \u00a0ssid=\"yourssid<\/strong>\"\n    psk=2a1f2e3c8d7f5e4a35c6f4e3d...<\/strong>\n\u00a0\u00a0 \u00a0proto=WPA\n\u00a0\u00a0 \u00a0key_mgmt=WPA-PSK\n\u00a0\u00a0 \u00a0pairwise=CCMP\n\u00a0\u00a0 \u00a0auth_alg=OPEN\n}<\/pre>\n
The PSK above is generated by using wpa_passphrase<\/strong> as follows:<\/p>\n
wpa_passphrase <ssid> <password><\/pre>\n
Since my SSID is hidden, I had to add the scan_ssid <\/strong>setting to make it find the network. Without this, it gives loads of errors about DHCP discover failing.<\/p>\n
Another problem I have had a few times is that if you make small typo in the wpa_supplicant file, it will fail to start with error 1.<\/p>\n
Having changed the settings, I restarted the wireless network as follows:<\/p>\n
sudo ifdown wlan0\nsudo ifup wlan0<\/pre>\n
This got it up and running on the network, and then I was able to SSH into the Pi.<\/p>\n
Next I decided to try an update as follows:<\/p>\n
sudo apt-get update\nsudo apt-get upgrade<\/pre>\n
As a quick check at this stage:<\/p>\n
uname -r\n4.1.13+<\/pre>\n
Configuring FBTFT for the HY28.<\/h2>\n
Next, I decided to install the FBTFT drivers for the LCD display. These are apparently now included in the Raspberry Pi Foundation kernel, so let’s try updating that:<\/p>\n
sudo rpi-update\nsudo reboot<\/pre>\n
Check the version:<\/p>\n
uname -r\n4.1.15+<\/pre>\n
Having connected the HY28A TFT LCD to the Pi via the SPI bus, I tried loading the drivers (using the same settings I had backed up from my previous working installation):<\/p>\n
# load the driver: the panel goes black\nsudo modprobe fbtft_device name=hy28a rotate=270 gpios=reset:25 fps=20\n# map console to LCD for testing\ncon2fbmap 1 1<\/pre>\n
Having done this, the console appeared on the LCD, confirming that it works. I then made it permanent by loading the module from\u00a0\/etc\/modules-load.d\/fbtft.conf<\/a><\/p>\n
spi-bcm2835\nfbtft_device<\/pre>\n
The\u00a0options are set in\u00a0\/etc\/modprobe.d\/fbtft.conf<\/a><\/p>\n
options fbtft_device name=hy28a rotate=270 gpios=reset:25 txbuflen=32768 fps=20<\/pre>\n
For reference only, the touchpanel driver settings used to be the following in \/etc\/modules (and haven’t yet been corrected for systemd as I don’t use them currently):<\/p>\n
# Touchpanel driver\nads7846_device pressure_max=255 y_min=190 y_max=3850 gpio_pendown=17 x_max=3850 x_min=230 x_plate_ohms=60 ads7846<\/pre>\n
To make the console appear during boot, I added the following to the end of \/boot\/cmdline.txt<\/strong>. This font seemed the best of the few that I tried.<\/p>\n
fbcon=map:10 fbcon=font:Acorn8x8<\/pre>\n
After about 30 minutes, the LCD screen goes blank. To disable this, I changed the BLANK_TIME and POWERDOWN_TIME to zero in \/etc\/kbd\/config<\/strong>:<\/p>\n
# prevent screen blanking\nBLANK_TIME=0\nPOWERDOWN_TIME=0<\/pre>\n
Installing the ADS1015 ADC board<\/h2>\n
For Raspbian, we first have to enable I2C by adding the following lines to \/etc\/modules<\/strong>:<\/p>\n
# I2C drivers for ADC board\ni2c-bcm2708\ni2c-dev<\/pre>\n
After a reboot, I installed i2c-tools<\/a> for convenience:<\/p>\n
sudo apt-get install python-smbus\nsudo apt-get install i2c-tools<\/pre>\n
Having done this, the following can be used to detect I2C devices:<\/p>\n
sudo i2cdetect -y 1\n# for older Raspberry Pi boards:\n# sudo i2cdetect -y 0<\/pre>\n
For my Pi, the ADS1015 appears as address 0x48<\/strong> on \/dev\/i2c-1<\/strong>. Having confirmed this, I wrote a small command-line test program to check that the ADC was working and returning voltage readings.<\/p>\n
With my buttons wired to the ADC via a resistor ladder, this was an opportunity to check that they worked as planned. With various button combinations, I obtained the following readings:<\/p>\n