St7565r Drivers For Mac
A display driver supports a particular family of display controllers. The drivers can be configured by modifying their configuration files whereas the driver itself. A4990MotorShield, Arduino library for the Pololu A4990 Dual Motor Driver. Arduino port of the LMIC (LoraWAN-MAC-in-C) framework provided by IBM.
The is going to enable a bunch of fun projects around here. Unfortunately, the library is a bit slow in one specific way – display updates. Since everything is buffered in RAM, most other operations are actually quite fast, but to get that data onto the gLCD takes time. I had to find out how much time, of course. Here’s my test sketch: All the loop does is send the same RAM buffer contents to the display, over and over again.
The time it takes in microseconds is sent to the serial port, and the result is quite bad, actually:. 126 milliseconds, i.e. 8 refreshes per second, max! The good news is that it’s a clear bottleneck, so chances are that it can be found and then hopefully also avoided. Sleuthing time! The ST7565 core primitives, responsible for getting the data out to the display were coded as follows: Guess what: the shiftOut in the Arduino library is written with calls to digitalWrite. That rings a bell.
Ah, yes, good OLD digitalWrite again, eh? So I rewrote this code using fixed pin numbers and direct port access: And sure enough, it’s almost exactly TEN times faster:.
12.3 milliseconds, i.e. 80 refreshes per second. Needless to say, I’m going to leave these changes in my copy of the ST7565 library – even though that means it’s no longer general purpose since the pin assignments are now hard-coded. A 10-fold performance increase of something which really needs to be snappy and responsive is non-negotiable for me.
Is a copy of the ST7565 code I use. Could this bottleneck have been avoided? The ST7565 library was clearly written as general purpose library, so making it usable with any set of pin assignments makes a lot of sense. The price paid in this case, was a 10-fold drop in performance, plus a few extra bytes of RAM used in the ST7565 class. I’ll revisit this topic some other time, to discuss the trade-offs and implications of compile-time vs run-time logic, as well as tricks such as: putting the pin choices in a header file, using #include for source files, pre-processing and code generation,. For now, I’m just happy with the 80 Hz refresh rate:) Update – I had to slow down the SPI clock a bit, because the display was not 100% reliable with the code shown above. The fix is in the file.
When you write to the display you have to write an entire byte, 8 pixels. I believe the bytes are arranged vertical on this display. So if you wanted to set all 8 pixels (which were in the same byte) to a specific pattern, then yes, you could write them direct to the LCD without any need to read the current contents. The problem occurs if you are not writing all 8 pixels in a byte, but maybe 6 from one byte, and 2 from the following byte below, or maybe not even 8. Maybe you just want to set 2. If you just write the bytes as they are, any other pixels set on the bytes you write to will be turned off.
St7565r Drivers For Macbook Pro
Now here’s where some shortcuts and speed increases might be available to grab. So far JC has shown us text information being displayed. He’s using a font which is based on the 6×8 layout (ah-ha 8 pixels high), and so far he’s been placing them in positions where Y%8=0, so we don’t care what is already in the byte, as our character is using all 8 vertical pixels in each of its 6 columns and it is aligned to the byte boundaries of the display, so in this situation, using the display as a 8 row text device, you could bypass the ram storage and write direct. I used to do a lot of direct display playing back in the days before windows, so as soon as my panel arrives I will be digging into the library like a man possessed (and discovering how bad my memory has become!).
I have a project in mind for my recently arrived pi. Basically, I'm thinking of wiring up a small graphical LCD via GPIO - small enough to fit on top of a modded case for the pi - that I can then control from the pi. In terms of front-end, I'm going to write a node.js server with web interface for controlling what's going on the display, as well as pulling in various bits of system information - so clock, date, number of unread emails, upcoming appointments, displaying a twitter feed, possibly SMS, and of course an AJAX api.
I may well end up fitting a speaker too for audio alerts. Combined with a wifi adapter, I could then have a headless pi with just power, with the lcd controllable remotely.
Would be a kick ass alarm clock if nothing else! Of course, I'll be sticking it all up on github, and hopefully blogging as I go.
I can handle the node.js coding no problem. I'd like to leave the USB ports alone for future use, especially as they're likely to be outside the case, and I don't really want trailing wires going outside, so the GPIO port seems ideal to keep it all tidy. I've looked at a lot of GLCDs now, and I'm thinking the would fit the bill (though I'll be getting it from a ) First, and most importantly, it uses 3.3V serial logic, which I understand to be important instead of 5V signalling. At 95mm x 55mm it's only slightly larger than the pi itself, so should be able to fit on a 'posts and 2 bits of perspex' case. Given it's an arduino display, the specs sheet seems fairly good. Plus, pretty backlight! Where I'm.very.
rusty is the electrical side of things - been 15 years since I last wielded a soldering iron! So I could definitely use some advice.
Here's my questions. 1) Am I right in thinking I can drive this thing via the GPIO port alone? The for arduino uses a 4050 to convert 5v signalling down to 3V for the display; which shouldn't be necessary for the pi as I understand it. The backlight is powered from 3.3V with a 100ohm resistor or 5V with a 270 ohm. I'm a bit concerned about current draw for the backlight; I've a 2 amp microUSB supply, which theoretically gives me 1300 milliamp to play with on the 5V GPIO supply line, and the lcd max draw is 500mA, though normal peak is 120mA. The 50mA limit on the 3V3 GPIO supply wouldn't be even close to sufficient, so the backlight will be on the 5V supply with resistor.
The logic/lcd supply only draw 1mA according to the spec sheet off the 3.3V supply, which seems low to me, but should work. Putting aside power, that leaves these lines: /CS - Chip Select - White /RST - Reset - Blue A0 - sometiimes called RS - Green SCLK - Serial clock - Yellow SID - Serial Input Data - Orange Which leads to my next question 2) How do I control this thing? I presume I can wire it up to the SPI GPIO pins - pi MOSI to SID, SCLK to SCLK. CS should be tied low I think to ensure serial mode, and CEO and CE1 for RST and A0 (data/command mode). Do I then use the bootc SPI kernel driver? Rpi.gpio python library?
Modify the arduino C library for the pi? Some combination of the above? I'm a sysadmin, so I'm pretty familiar with bash scripting, client-side and server-side JS (i.e.
Node.js) with a smattering of PHP and C on linux boxes, and compiling my own kernel holds no fears, but I'm a complete newb on the mechanics of getting data out to the serial bus. 3) final optional question. The backlight LCD colours are done by PWM. Is there any way to control this from GPIO18-ALT5 PWM0, given the current requirement of the backlight has to come from the 5V supply? Similarly, can you see a way to turn the current on/off to the backlight via software control?
I can put an additional chip in for this purpose if needed, but given I'm going to be cramped for space I'd like to avoid putting in a gertboard or the like! So any advice you can offer - especially if I'm barking up the wrong tree electrically speaking for driving an ST7565 directly from the GPIO expansion port would be much appreciated! 2) How do I control this thing? I presume I can wire it up to the SPI GPIO pins - pi MOSI to SID, SCLK to SCLK. CS should be tied low I think to ensure serial mode, and CEO and CE1 for RST and A0 (data/command mode). Do I then use the bootc SPI kernel driver? Rpi.gpio python library?
Modify the arduino C library for the pi? Some combination of the above? After several hours more research, I think I'm getting closer to answering this one for myself. I'd misunderstood the SPI interface, and the needed pins. Has been really helpful on how the ST7565 works. Set the A0 pin low to indicate that command data is being sent Set the chip select (CS) pin low Send each bit of the command, starting with the most significant bit and working down to the least significant Set the chip select (CS) pin high, to free the bus For example; and data is sent by putting high/low on the SID line, and then cycling the SCLK line.
So I will need to control RST, A0, CS, SID and SCLK. Pi SCK - Shift Clock = SCLK pi MOSI - Master Out Slave In = SID Still need to figure out how to connect and control RST, A0 and CS though. Software wise, definitely looks like the bootc kernel with SPI support is the way to go, along with ioctl. To do that, I'll need a SPI client driver for the ST7565; hopefully I'll be able to re-use some of the adafruit reference code for this. Plenty to learn, I think.
3) final optional question. The backlight LCD colours are done by PWM. Is there any way to control this from GPIO18-ALT5 PWM0, given the current requirement of the backlight has to come from the 5V supply? Similarly, can you see a way to turn the current on/off to the backlight via software control? I can put an additional chip in for this purpose if needed, but given I'm going to be cramped for space I'd like to avoid putting in a gertboard or the like! After doing a lot more reading about driving LEDs with the pi, I've found a different datasheet for the adafruit ST7565 -, in fact. That's linked from the negative ST7565, and shows there's actually a couple of extra LED lines for the backlight, which makes a lot more sense.
They share a common anode, with separate cathodes for red, green and blue. Also has the specs for the leds - 2.0V for the red, 3.1V for the green and blue, and 18mA for the forward current on all. They don't specify whether that's maximum forward current, but I'm going to assume it is (they do specify an absolute 500mA maximum forward current for the backlight, but I don't trust that). I did find a forum post on the ladyada forum where it was recommended to not drive them over 20mA. Normally with the arduino, the LEDs are driven at 3.3V with inline resistors, and then the cathodes are connected to PWM pins - so that the effective voltage can be controlled, and get graduations of each colour. Given the lack of PWM pins on the pi, I'm going to forget about that side of things. What I will have to do is use transistors to switch on/off the ground line for each LED colour plus inline resistor, so I can still have a choice of 6 colours plus white and off altogether under software control.Rather put the transistor on the anode side, but can't with this backlight; so will have to figure out how to do that safely and not fry the transistor.
St7565r Drivers For Mac
It's not ideal to put the resistor in the cathode line either, due to the chance of accidentally shorting the cathode directly to ground and blowing the led, but given we've got a shared anode, there's not much choice. The other option would be to drive them at 3.3V from the pi, rather than the 5V line from the microUSB; given the shared anode, you'd have to tie the 3.3V supply line to the anode, then have 3 tied-high GPIO pins with an inline resistor to the individual cathodes - when the signal is high, no current would flow, and when connected to ground, you'd dump the current through the led and resistor, and dump it into the signal lines on the GPIO. If you kept the current under control, say 10mA per LED, you wouldn't overdrive the 3.3V source; but I've no idea how much drain current the individual pins on the GPIO can take, and I'd rather blow the LED backlight than the pi, given how hard it is to get hold of!
And given you'd be dumping 3.1 out of 3.3V into the green and blue leds, you'd have to have a tiny resistor - and that doesn't give you much room for tolerance - slightly out of whack, you draw too much current, and pop there goes the pi. So I think I'm gonna drive the LEDs with the 5v line, and try to make damn sure I don't short the 5V line to any pins on the GPIO, or again, pop goes the pi. Next step is going to be drawing up a circuit diagram and breadboard layout so I'm all ready to roll on that front when the bits turn up. Just need to find a good circuit diagrammer for osx or ubuntu. I've also got bootc's 3.2.20 kernel with the SD performance patches that he put up yesterday cross-compiled and running on my pi, so that enables the SPI interface - first time I've had the 3.2 kernel running successfully on my sandisk SD card without MMC errors. Given they've changed the SPI setup to require compiling custom kernels to add SPI client drivers, looks like I'm definitely going to have to dust off my C skills as well as my electronics to port the adafruit driver to the kernel, and figure out how I'm going to control the A0, RST and backlight GPIO pins in addition to the SPI data lines. That'll keep me busy for a while!
Thank you so much for posting about this! I'd like to get an ST7565 and use it also. If you could help, that would be great. The DS1339 - that's not for driving the ST7565 at all, is it? If you can share the other parts between the Pi and the ST7565, that would help me a lot. I don't know what resistors or whatever goes between the two - burning the LCD or the Pi scares me.
If you want help with the C code, I might be able to help with that. Thank you again for sharing! Display posts from previous: Sort.