The project I was working on recently was to get the Digispark module to act as a Linux I2C-to-USB driver. It wasn't all so straight forward so I decided to put a little put a little tutorial on how to do it.
That's how the breadboard version of it looks like
Let's get to hacking!
Requirements
You will obviously need a Digispark or a clone of it. I used one I bought from aliexpress.com and it does the trick quite nicely
Let's assume you don't have the micronucleus bootloader installed and let's build one from scratch. You'll need a AVR programmer like USBasp (cheap and does the job very well)
| git clone git@github.com:micrnucleus/micrnucleus | |
| cd micronucleus/commandline | |
| make | |
| sudo cp micronucleus /usr/local/bin | |
| cd ../firmware | |
| make clean hex | |
| avrdude -c usbasp -p t85 -U flash:w:main.hex |
Done. In case you're missing any libraries or tools that's the list of packages that is required
build-essential, avrdude, avr-libc, binutils-avr gcc-avr
You'll also need an LCD with PCF8547A or PCF8547T extender. I used one with T which required me to apply a patch to the LCDProc sources. More on that soon
The project
First we need the littlewire version of the firmware for our Digispark. You can get it form github
git clone https://github.com/nopdotcom/i2c_tiny_usb-on-Little-WireBuinding it and installing onto your Digispark is very straight-forward and described in details here.
Let's get to the hacky part of it!
Patching LittleWire firmware
As it turns out the original driver for i2c-tiny-usb was reluctant to recognize the hardware as proper I2C adapter. I needed to update the vendor and device IDs to make it work
| diff --git a/firmware/usbconfig.h b/firmware/usbconfig.h | |
| index a51c68d..cc0385d 100644 | |
| --- a/firmware/usbconfig.h | |
| +++ b/firmware/usbconfig.h | |
| @@ -115,7 +115,7 @@ extern void usbEventResetReady(void); | |
| /* -------------------------- Device Description --------------------------- */ | |
| -#define USB_CFG_VENDOR_ID 0xc0, 0x16 /* = 0x16c0 = 5824 = voti.nl */ | |
| +#define USB_CFG_VENDOR_ID 0x40, 0x1c /* = 0x16c0 = 5824 = voti.nl */ | |
| /* USB vendor ID for the device, low byte first. If you have registered your | |
| * own Vendor ID, define it here. Otherwise you may use one of obdev's free | |
| * shared VID/PID pairs. Be sure to read USB-IDs-for-free.txt for rules! | |
| @@ -124,7 +124,7 @@ extern void usbEventResetReady(void); | |
| * with libusb: 0x16c0/0x5dc. Use this VID/PID pair ONLY if you understand | |
| * the implications! | |
| */ | |
| -#define USB_CFG_DEVICE_ID 0xdc, 0x05 /* = 0x05dc = 1500 */ | |
| +#define USB_CFG_DEVICE_ID 0x34, 0x05 /* = 0x05dc = 1500 */ | |
| /* This is the ID of the product, low byte first. It is interpreted in the | |
| * scope of the vendor ID. If you have registered your own VID with usb.org | |
| * or if you have licensed a PID from somebody else, define it here. Otherwise |
After building it and installing again on the Digispark and loading the i2c-tiny-usb and i2c-dev modules using modprobe the command i2cdetect -l finally started spitting out some good news :)
padcom@aphrodite:~$ sudo i2cdetect -l
i2c-0 i2c i915 gmbus ssc I2C adapter
i2c-1 i2c i915 gmbus vga I2C adapter
i2c-2 i2c i915 gmbus panel I2C adapter
i2c-3 i2c i915 gmbus dpc I2C adapter
i2c-4 i2c i915 gmbus dpb I2C adapter
i2c-5 i2c i915 gmbus dpd I2C adapter
i2c-6 i2c DPDDC-B I2C adapter
i2c-7 i2c DPDDC-C I2C adapter
i2c-8 i2c i2c-tiny-usb at bus 001 device 057 I2C adapterAfter hooking up the LCD to pins 0 (SDA) and 2 (SCL) and adding 2 4.7k pull-up resistors the LCD has been properly recognized as well :)
padcom@aphrodite:~$ sudo i2cdetect 8
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-8.
I will probe address range 0x03-0x77.
Continue? [Y/n]
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- 27 -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- -- Success! Well, actually to get to this point took me over 2 days to figure out all the moving parts but the joy of having it actually working was just great :)
Now it's time to do some serious work with that new piece of hardware we have. Let's use LCDProc to display some system statistics!. Download, extract... and if you're using the PCF8547T version of the extender apply the following patch before building:
| --- server/drivers/hd44780-i2c.c 2014-03-23 11:22:09.000000000 +0100 | |
| +++ server/drivers/hd44780-i2c.c 2015-12-27 00:55:15.528659000 +0100 | |
| @@ -85,10 +85,10 @@ | |
| void i2c_HD44780_backlight(PrivateData *p, unsigned char state); | |
| void i2c_HD44780_close(PrivateData *p); | |
| -#define RS 0x10 | |
| -#define RW 0x20 | |
| -#define EN 0x40 | |
| -#define BL 0x80 | |
| +#define RS 0x01 | |
| +#define RW 0x02 | |
| +#define EN 0x04 | |
| +#define BL 0x08 | |
| // note that the above bits are all meant for the data port of PCF8574 | |
| #define I2C_ADDR_MASK 0x7f | |
| @@ -191,12 +191,12 @@ | |
| if (p->port & I2C_PCAX_MASK) { // we have a PCA9554 or similar, that needs special config | |
| char data[2]; | |
| - data[0] = 2; // command: set polarity inversion | |
| + data[0] = 2 << 4; // command: set polarity inversion | |
| data[1] = 0; // -> no polarity inversion | |
| if (write(p->fd,data,2) != 2) { | |
| report(RPT_ERR, "HD44780: I2C: i2c set polarity inversion failed: %s", strerror(errno)); | |
| } | |
| - data[0] = 3; // command: set output direction | |
| + data[0] = 3 << 4; // command: set output direction | |
| data[1] = 0; // -> all pins are outputs | |
| if (write(p->fd,data,2) != 2) { | |
| report(RPT_ERR, "HD44780: I2C: i2c set output direction failed: %s", strerror(errno)); | |
| @@ -210,43 +210,43 @@ | |
| // powerup the lcd now | |
| /* We'll now send 0x03 a couple of times, | |
| * which is in fact (FUNCSET | IF_8BIT) >> 4 */ | |
| - i2c_out(p, 0x03); | |
| + i2c_out(p, 0x30); | |
| if (p->delayBus) | |
| hd44780_functions->uPause(p, 1); | |
| - i2c_out(p, enableLines | 0x03); | |
| + i2c_out(p, enableLines | 0x30); | |
| if (p->delayBus) | |
| hd44780_functions->uPause(p, 1); | |
| - i2c_out(p, 0x03); | |
| + i2c_out(p, 0x30); | |
| hd44780_functions->uPause(p, 15000); | |
| - i2c_out(p, enableLines | 0x03); | |
| + i2c_out(p, enableLines | 0x30); | |
| if (p->delayBus) | |
| hd44780_functions->uPause(p, 1); | |
| - i2c_out(p, 0x03); | |
| + i2c_out(p, 0x30); | |
| hd44780_functions->uPause(p, 5000); | |
| - i2c_out(p, enableLines | 0x03); | |
| + i2c_out(p, enableLines | 0x30); | |
| if (p->delayBus) | |
| hd44780_functions->uPause(p, 1); | |
| - i2c_out(p, 0x03); | |
| + i2c_out(p, 0x30); | |
| hd44780_functions->uPause(p, 100); | |
| - i2c_out(p, enableLines | 0x03); | |
| + i2c_out(p, enableLines | 0x30); | |
| if (p->delayBus) | |
| hd44780_functions->uPause(p, 1); | |
| - i2c_out(p, 0x03); | |
| + i2c_out(p, 0x30); | |
| hd44780_functions->uPause(p, 100); | |
| // now in 8-bit mode... set 4-bit mode | |
| - i2c_out(p, 0x02); | |
| + i2c_out(p, 0x20); | |
| if (p->delayBus) | |
| hd44780_functions->uPause(p, 1); | |
| - i2c_out(p, enableLines | 0x02); | |
| + i2c_out(p, enableLines | 0x20); | |
| if (p->delayBus) | |
| hd44780_functions->uPause(p, 1); | |
| - i2c_out(p, 0x02); | |
| + i2c_out(p, 0x20); | |
| hd44780_functions->uPause(p, 100); | |
| // Set up two-line, small character (5x8) mode | |
| @@ -280,8 +280,8 @@ | |
| i2c_HD44780_senddata(PrivateData *p, unsigned char displayID, unsigned char flags, unsigned char ch) | |
| { | |
| unsigned char enableLines = 0, portControl = 0; | |
| - unsigned char h = (ch >> 4) & 0x0f; // high and low nibbles | |
| - unsigned char l = ch & 0x0f; | |
| + unsigned char h = ch & 0xf0; // high and low nibbles | |
| + unsigned char l = ch << 4; | |
| if (flags == RS_INSTR) | |
| portControl = 0; |
All that is left is to configure and build and configure the LCDProc package. Tested also on Raspberry Pi 2 and works flawlessly.
./configure --enable-drivers=hd44780 && make && sudo make installNow edit the /usr/local/etc/LCDd.conf file as follows
DriverPath=/usr/local/lib/lcdproc/
Driver=hd44780
ServerScreen=offAnd under the section [hd44780] make sure you have the following values
ConnectionType=i2c
Device=/dev/i2c-8 # that is the I2C bus id you have from i2cdetect -l
Port=0x27 # that is the I2C device id you have from i2cdetect 8Starting it all up
First start the LCDd daemon. You might want to start it initially with the -f (foreground) parameter to check if it works ok.
LCDd -fNext you need to run the client. Yes! It is a client-server architecture! Use lcdproc --help for the list of all available options. I use the SMP-CPU version the most
lcdproc -f PThat's it! I admit this is more hassle that I generally like but getting it working is worth every late night minute I spent on it :)
Happy hacking!
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