a) How is the OLED in the zedboard internally connected, is it through SPI, GPIOs or the PL. If it's through SPI/GPIOs then which pins?
First or second result for the web search "zedboard oled pdf" - http://zedboard.org/sites/default/files/ZedBoard_HW_UG_v1_1.pdf
then search for "oled" in it (page numbers of the pdf file, not printed in document):
page3: 2.4.4 OLED...... ... ...... 19
page4: 128x32 OLED Display
page5: ZYNQ XC7Z020-CSG484 OLED <- bus_of_5 -> 128x32 OLED
page20: 2.4.4 OLED
An Inteltronic/Wisechip UG-2832HSWEG04 OLED Display is used on the ZedBoard. This
provides a 128x32 pixel, passive-matrix, monochrome display. The display size is 30mm x11.5mm x 1.45mm. Table 11 - OLED Connections ... Interface
oled_pin symb EPP_pin Function
9 RES# U9 Power Reset for Controller and Driver
8 CS# N/C Chip Select – Pulled Down on Board
10 D/C# U10 Data/Command Control
11 SCLK AB12 Serial Clock Input Signal
12 SDIN AA12 Serial Data Input Signal
So, we know model of OLED UG-2832HSWEG04 (datasheet http://www.adafruit.com/datasheets/UG-2832HSWEG04.pdf with low-level details on data interface) and data connection; this is OLED with 1 serial data input and 1 serial clock.
Pinout pdf is http://www.xilinx.com/support/documentation/user_guides/ug865-Zynq-7000-Pkg-Pinout.pdf (too long to read), but there is shorter version of pin list in txt format: http://www.xilinx.com/support/packagefiles/z7packages/xc7z020clg484pkg.txt
Device/Package xc7z020clg484 9/18/2012 10:07:35
Pin Pin Name Memory Byte Group Bank VCCAUX Group Super Logic Region I/O Type
AA12 IO_L7P_T1_13 1 13 NA NA HR
AB12 IO_L7N_T1_13 1 13 NA NA HR
HR means "3.3V-capable high-range (HR) banks", both data pins are from "bank 13". Pin name is IO_* so it "supports both input, as well as output functionality", and is part of "PL Pins" (PL = programmable logic = FPGA). Default Zedboard firmware of FPGA part gives access to this pin to the ARM part of chip with linux kernel (PS = processing system = ARM) by routing it to some internal processing_system GPIO pin via system.ucf file like:
NET processing_system7_0_GPIO_pin[5] LOC = AB12 | IOSTANDARD="LVCMOS25"; # "OLED-SCLK"
NET processing_system7_0_GPIO_pin[6] LOC = AA12 | IOSTANDARD="LVCMOS25"; # "OLED-SDIN"
Then the GPIO pins are registered in devicetree (dts) https://github.com/Digilent/linux-digilent/blob/master/arch/arm/boot/dts/digilent-zed.dts in zed_oled group:
zed_oled {
compatible = "dglnt,pmodoled-gpio";
/* GPIO Pins */
vbat-gpio = <&ps7_gpio_0 55 0>;
vdd-gpio = <&ps7_gpio_0 56 0>;
res-gpio = <&ps7_gpio_0 57 0>;
dc-gpio = <&ps7_gpio_0 58 0>;
/* SPI-GPIOs */
spi-bus-num = <2>;
spi-speed-hz = <4000000>;
spi-sclk-gpio = <&ps7_gpio_0 59 0>;
spi-sdin-gpio = <&ps7_gpio_0 60 0>;
};
b) Any tutorial or documentation that I can follow to create userspace drivers using SPI/GPIO for the OLED in the zedboard?
According to Avnet's Getting Started pdf, "Demo 2 – OLED Display" scetion on page 17 (web searched as "zedboard oled") http://zedboard.org/sites/default/files/documentations/GS-AES-Z7EV-7Z020-G-14.1-V6%5B1%5D.pdf#page=17 there is kernel driver pmodoled-gpio.ko (on screenshot it reported as "pmodoled-gpio-spi"), so OLED is driven with GPIO pins.
There are two helper scripts: unload_oled to remove the kernel module and load_oled to insert it into kernel. Driver will create special device file /dev/zed_oled to work with display from user-space and load_oled also displays the /root/logo.bin file using this zed_oled interface.
Typical usage of zed_oled is like cat yourfile.bin > /dev/zed_oled, for example http://people.mech.kuleuven.be/~lin.zhang/notes/emebedded-linux/zedboard-oled-display.html and better http://zedboard.org/content/zedboard-oled
The .bin file format. ... The screen is written to right to left, top to bottom with each pixel being represented by a bit within one of the bytes within the .bin file. Bits are read-in top down 8 pixels then move over 1 pixel and write the next 8 bits and continue until you are at the end of the row. Then move down 8 pixels and do this again 3 more times.
You can do writes from C application, check code from http://www.cnblogs.com/popo0904/p/3853144.html (you can use online web translation services to read the text)
Documentation on the kernel module PmodOLED used in standard zedboard demo: https://github.com/Digilent/linux-digilent/blob/master/Documentation/pmods/pmodoled.txt
The driver provides a 512 Byte display buffer for the display of PmodOLED.
The Whole screen is divided into four lines, each of them is 128 bits wide
and 8 bits high, as shown in the figure below.
+--------------------------...----------------------------+
+ Line 4 +
+--------------------------...----------------------------+
+ Line 3 +
+--------------------------...----------------------------+
+ Line 2 +
+--------------------------...----------------------------+ MSB (bit 7)
+ Line 1 +
+--------------------------...----------------------------+ LSB (bit 0)
byte 127 byte 0
Users can perform read and write functions to the device node to access the data
inside the display buffer.
And there is source code of the dirver: https://github.com/Digilent/linux-digilent/blob/06b388903e5459687ba2538ae3895ffe29e2e39e/drivers/pmods/pmodoled-gpio.c
c) I have a redhat desktop, is there any SDk I can use to develop userspace drivers for the zedboard from my redhat desktop.
The standard driver is kernel-space for this OLED on ZEDboard, you can use it from precompiled ZEDboard firmware. Or you can build the kernel according to zedboard instructions, all in-kernel drivers will be built too (if enabled in kernel configuration): http://zedboard.org/content/creating-linux-kernel-image-boot-zc702-sd-card-slot