#custom driver

I am using a NOOB version for getting up and running with the Rasberry Pi. The version of my Raspberry Pi is 3 Model B (see below):

Format a micro SD card

For formatting the micro SD card I usually use the gparted utility in Ubuntu. Format the micro SD with FAT 32 filesystem format. You need to have a SD card reader for attaching the SD card to the PC. I use the below SD card and the reader for my purposes:

Once you have attached your SD card with the linux PC you are ready to format it. I am using a Ubuntu PC for my purposes. Go to the console and run the below command:

~$ sudo gparted

By default the gparted selects your hard drive (/dev/sda is actually your hard drive, did you know!). Be very cautious, not to play around with your hard drive partitions, you might soon get into a funny situation. So go to the top right corner of the gparted screen and change the drive from /dev/sda to /dev/sdb (if there are no other media attached to the PC). Look at the various field carefully and try to understand what they are. I cannot go into the details of all the fields here. What we are up to is delete everything in the SD card and get it ready for the NOOBS. I can see the below in my SD card (/dev/sdb) at the moment:

You can also see the same partitions with lsblk command on the console, I can see the below:

sda 8:0 0 465.8G 0 disk ├─sda1 8:1 0 512M 0 part /boot/efi └─sda2 8:2 0 465.3G 0 part / sdb 8:16 1 29.7G 0 disk ├─sdb1 8:17 1 2.4G 0 part ├─sdb2 8:18 1 1K 0 part ├─sdb5 8:21 1 32M 0 part ├─sdb6 8:22 1 256M 0 part └─sdb7 8:23 1 27.1G 0 part As you can see above the SD card has in total 5 partitions /dev/sdb1, /dev/sdb2, /dev/sdb5, /dev/sdb6, /dev/sdb7. I want to get rid of all of these. So what I do in gparted screen is to select/highlight each partition, right click, and then Unmount. Once the selected/highlighted partition has been Unmounted, you can right click and Delete it. Unmount and Delete each of these partitions in the SD card. Now Click on the green Tick at the top of the gparted screen and Apply. At this point you would have unallocated partition like this:

Right click on the Unallocated partition and click on New. Leave everything as default except Filesystems as FAT32, the default is ext4.

After changing the file systems type it should look like the below:

Click Add. Then again click on the green Tick button at the top, then Apply. Once done, you should see something like the below:

Now, close gparted and go back to your favourite file browser and locate the SD card, in my case it shows something like the below, an empty drive:

Get hold of the NOOBS

Go to the below link:

https://www.raspberrypi.org/downloads/

Click on the Download ZIP and you will get the latest vesion of the NOOBS. Or if you need a different NOOBS version other than the latest, you can get a copy of that in the below link:

http://downloads.raspberrypi.org/NOOBS/images/

For my purposes I have download the NOOBS_v3_2_1 version (NOOBS_v3_2_1.zip) from the above link. Choose the one you need and move to the next step.

Once you have downloaded the NOOB version you want, extract the NOOBS and you should have a folder called something like NOOBS_*_*. In my case it is NOOBS_v3_2_1. Go inside the folder using your file browser, select and copy everything (Ctrl-A, Ctr-C). Go back to the SD card and do a Ctrl-V. This will copy and paste everything that the NOOBS_v3_2_1 had into the SD card.

Be patient, it takes a while to copy the stuffs across into the SD card. I often make mistake of prematurely eject the drive and nothing works! So be patient! There is a circular progress bar is whirling around at the top on the file browser window, if you have noticed. Once everything copied into the SD card, safely eject the drive and insert it into the SD card slot in Pi.

Now, connect the below to the Pi:

A keyboard.

A monitor/TV

A mouse (very useful)

Connect the Pi using micro USB cable to the PC to power it up.

Once you have powered the Pi, the NOOBS will take care of booting the device and soon you should see something like this on the Monitor:

Select the Raspberry Pi Full option from the menu shown above. You will require at least ~8GB I guess. Other option is to select the LibreELEC_RPi2 which I won’t recommend at this point. After you select one option from the menu, the “install” button will get activated. Click on Install. See the below pictures for reference:

Once you have clicked on the Install the installation starts:

Wait for the installation to finish. After the installation the setup wizard comes up, follow the screens and setup the Country, Language and Timezone etc. Keep the default user account ‘pi’ and password ‘raspberry’. It may ask for restart, do restart.

Find the kernel version of NOOBS installation

Go to Pi and open a terminal. Then type the below: pi@raspberrypi:~ $ uname -a Linux raspberrypi 4.19.75-v7+ #1270 SMP Tue Sep 24 18:45:11 BST 2019 armv7l GNU/Linux In the above it shows the kernel version this NOOBS installation has is 4.19.75-v7+. Now, for cross compilation we need the exact version of the Kernel source code, otherwise we will get the below error: pi@raspberrypi:~ $ sudo insmod GobiNet.ko insmod: ERROR: could not insert module GobiNet.ko: Invalid module format Linux kernels for Raspberry Pi is located here:

https://github.com/raspberrypi/linux

By default the one coming right now is version 4.19.y. This doesn’t exactly match with the one we need i.e. 4.19.75-v7+. Next you can look into the Branches here:

https://github.com/raspberrypi/linux/branches

However, I cannot see the exact match. So now I look into the Releases tab. This looks like has the one we want:

https://github.com/raspberrypi/linux/releases

In this page I can see the Kernel release which was on the 24th Sep, 2019. This exactly matches with the one in NOOBS: pi@raspberrypi:~ $ uname -a Linux raspberrypi 4.19.75-v7+ #1270 SMP Tue Sep 24 18:45:11 BST 2019 armv7l GNU/Linux

Download this Kernel source code in your local machine (Ubuntu in my case). The tarball is called linux-raspberrypi-kernel_1.20190925-1.tar.gz. Extract the tarball with the below command: tar -xvf linux-raspberrypi-kernel_1.20190925-1.tar.gz In my setup after extraction the linux source is located in the below path: /home/vbhadra/Downloads/linux-raspberrypi-kernel_1.20190925-1 Now, go inside the linux kernel source folder and do th below: cd /home/vbhadra/Downloads/linux-raspberrypi-kernel_1.20190925-1 make mrproper This will ensure we have started with a clean kernel source. Now, come to your Pi again. What we need now is the kernel configuration which was used for the NOOBS kernel compilation. The Kernel configuration now a days kept in the kernel itself as a module. So to grab hold of the kernel .config file do the below in Pi: pi@raspberrypi:~ $ sudo modprobe configs pi@raspberrypi:~ $ zcat /proc/config.gz > /tmp/.config Copy this .config file in a sd card and bring it back to the Ubuntu PC where your downloaded Kernel source tree lives. Then copy the .config file into the linux kernel source tree as below: vbhadra@vbhadra-8200-elit-convertable-microtower:~/Downloads/linux-raspberrypi-kernel_1.20190925-1$ sudo mount /dev/sdb1 ~/usb/ vbhadra@vbhadra-8200-elit-convertable-microtower:~/Downloads/linux-raspberrypi-kernel_1.20190925-1$ ls -la ~/usb/ total 748 -rw-r--r-- 1 vbhadra vbhadra 163003 Sep 26 02:23 .config vbhadra@vbhadra-8200-elit-convertable-microtower:~/Downloads/linux-raspberrypi-kernel_1.20190925-1$ cp ~/usb/.config .

Download the Pi toolchain

You will need the toolchain to cross compile the Kernel and your module for Pi environment. Download the toolchain from the git hub with the below command: git clone https://github.com/raspberrypi/tools ~/tools Locate where your tools folder is. I usually create a rpi folder in my home folder and do everything there. So in my setup it is located here: /home/vbhadra/rpi/tools Now, you need to point where your tools (cross compiler) is for compiling the kernel. To do that do the below: export CCPREFIX=/home/vbhadra/rpi/tools/arm-bcm2708/arm-bcm2708-linux-gnueabi/bin/arm-bcm2708-linux-gnueabi- Compile the kernel to create the Module.symvers file. To compile the kernel do the below in your Ubuntu setup: make ARCH=arm CROSS\_COMPILE=${CCPREFIX} -j 12 Let the above compile the Kernel which will take a while, wait patiently!

Now check if you have got a file created called in your linux folder: vbhadra@vbhadra-8200-elit-convertable-microtower:~/Downloads/linux-raspberrypi-kernel_1.20190925-1$ ls -la Module.symvers -rw-r--r-- 1 vbhadra vbhadra 841463 Feb 12 13:31 Module.symversCross

Compile your module

I am trying to cross compile GobiNet and GobiSerial drivers fro SieraWireless LTE device EM7565.

You can grab hold of the driver rom SieraWireless website. This is not about any specific driver and their intricacies. We will only focus on the important bits to cross compile any custom driver for Raspberry Pi (hw version 3 B).

So One you have any driver code which has been compiled for any other platform (possibly) and you want to cross compile it, first thing you should do is to look at the driver Makefile. In this case, I have the below driver Makefile for GobiNet driver:

obj-m := GobiNet.o GobiNet-objs := GobiUSBNet.o QMIDevice.o QMI.o KDIR := /lib/modules/$(shell uname -r)/build PWD := $(shell pwd) OUTPUTDIR=/lib/modules/`uname -r`/kernel/drivers/net/usb/ #KBUILD_CFLAGS += -DQOS_SIMULATE #KBUILD_CFLAGS += -DTX_XMIT_SIERRA -DTX_URB_MONITOR ifdef TX_URB_MONITOR ifeq ($(TX_URB_MONITOR), 1) KBUILD_CFLAGS += -DTX_XMIT_SIERRA -DTX_URB_MONITOR else TX_URB_MONITOR:=0 endif else TX_URB_MONITOR:=0 endif ifeq ($(TX_URB_MONITOR), 1) ccflags-y:=-DTX_URB_MONITOR GobiNet-objs += usbnet_3_0_6.o \ usbnet_2_6_35.o usbnet_3_10_21.o usbnet_3_12_xx.o usbnet_4_4_xx.o endif

RAWIP := 0 ifeq ($(RAWIP), 1) ccflags-y:=-DDATA_MODE_RP endif

#PI_KDIR := ~/k/linux-rpi-3.6.y #PI_KDIR := /home/vbhadra/Downloads/linux-rpi-4.19.y-rt PI_KDIR := /home/vbhadra/Downloads/linux-raspberrypi-kernel_1.20190925-1 #PI_CCPREFIX=~/toolchain/rpi/tools-master/arm-bcm2708/arm-bcm2708-linux-gnueabi/bin/arm-bcm2708-linux-gnueabi- PI_CCPREFIX=/home/vbhadra/rpi/tools/arm-bcm2708/arm-bcm2708-linux-gnueabi/bin/arm-bcm2708-linux-gnueabi-

OW_KDIR := ~/openwrt/trunk/build_dir/target-mips_r2_uClibc-0.9.33.2/linux-ar71xx_generic/linux-3.8.11 OW_CCPREFIX=~/openwrt/trunk/staging_dir/toolchain-mips_r2_gcc-4.6-linaro_uClibc-0.9.33.2/bin/mips-openwrt-linux-

MARVELL_KDIR := ~/toolchain/qmi_mxwell/kernel-2.6.31 MARVELL_CCPREFIX := ~/toolchain/qmi_mxwell/toolchain/bin/arm-none-linux-gnueabi-

M64_KDIR := ~/toolchain/arm64bit/linux/linux-4.4.1-devel-16.04.1 M64_CCPREFIX := ~/toolchain/arm64bit/be/aarch64ebv8-marvell-linux-gnu-5.2.1_x86_64_20151117/bin/aarch64_be-marvell-linux-gnu-

PPC_KDIR := ~/toolchain/ppc/kernel_ppc PPC_CCPREFIX :=~/toolchain/ppc/fsl/1.1/sysroots/i686-fslsdk-linux/usr/bin/ppc64e5500-fsl-linux/powerpc64-fsl-linux-

HIKEY9_KDIR := /farm/android/Hikey_9.0_Trunk/kernel/hikey-linaro HIKEY9_CCPREFIX := /farm/android/Hikey_9.0_Trunk/prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9/bin/aarch64-linux-android-

all: $(MAKE) -C $(KDIR) M=$(PWD) modules

m64: $(MAKE) ARCH=arm64 CROSS_COMPILE=${M64_CCPREFIX} -C $(M64_KDIR) M=$(PWD) modules

ppc: $(MAKE) ARCH=powerpc CROSS_COMPILE=${PPC_CCPREFIX} -C $(PPC_KDIR) M=$(PWD) modules

marvell: $(MAKE) ARCH=arm CROSS_COMPILE=${MARVELL_CCPREFIX} -C $(MARVELL_KDIR) M=$(PWD) modules

pi: $(MAKE) ARCH=arm CROSS_COMPILE=${PI_CCPREFIX} -C $(PI_KDIR) M=$(PWD) modules

ow: $(MAKE) ARCH=mips CROSS_COMPILE=${OW_CCPREFIX} -C $(OW_KDIR) M=$(PWD) modules

hikey9: $(MAKE) ARCH=arm64 CROSS_COMPILE=${HIKEY9_CCPREFIX} -C $(HIKEY9_KDIR) M=$(PWD) modules

install: all mkdir -p $(OUTPUTDIR) cp -f GobiNet.ko $(OUTPUTDIR) depmod

clean: #rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions Module.* modules.order .cache.mk *.o.ur-safe make -C $(PI_KDIR) M=$(PWD) clean

The only thing we are interested here is the target, in this file there is a target type called “pi”, that’s the one we want. Look deeper into this target and associated macros: pi: $(MAKE) ARCH=arm CROSS_COMPILE=${PI_CCPREFIX} -C $(PI_KDIR) M=$(PWD) modules Notice the CROSS_COMPILE is set to PI_CCPREFIX which is what you need to fix. In this example we have discussed about the tools we will use for asp Pi Kernel compilation. The same tool will come handy here as well. Point the PI_CCPREFIX to your tool/cross compiler path as below:

PI_CCPREFIX=/home/vbhadra/rpi/tools/arm-bcm2708/arm-bcm2708-linux-gnueabi/bin/arm-bcm2708-linux-gnueabi- Other important macro is this PI_KDIR. This points to the Kernel folder against which we are going to cross compile. Point this to your previosuly downloaded kernel source folder as below: PI_KDIR := /home/vbhadra/Downloads/linux-raspberrypi-kernel_1.20190925-1 I also modified the clean target as below: clean: make -C $(PI_KDIR) M=$(PWD) clean But this is not necessary. Save these changes and go back to the driver folder and issue the make clean command to start with a clean slate and then issue make pi command as below: vbhadra@vbhadra-8200-elit-convertable-microtower:~/rpi/GobiNet$ make clean #rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions Module.* modules.order .cache.mk *.o.ur-safe make -C /home/vbhadra/Downloads/linux-raspberrypi-kernel_1.20190925-1 M=/home/vbhadra/rpi/GobiNet clean make[1]: Entering directory '/home/vbhadra/Downloads/linux-raspberrypi-kernel_1.20190925-1' make[1]: Leaving directory '/home/vbhadra/Downloads/linux-raspberrypi-kernel_1.20190925-1' vbhadra@vbhadra-8200-elit-convertable-microtower:~/rpi/GobiNet$ make pi make ARCH=arm CROSS_COMPILE=/home/vbhadra/rpi/tools/arm-bcm2708/arm-bcm2708-linux-gnueabi/bin/arm-bcm2708-linux-gnueabi- -C /home/vbhadra/Downloads/linux-raspberrypi-kernel_1.20190925-1 M=/home/vbhadra/rpi/GobiNet modules make[1]: Entering directory '/home/vbhadra/Downloads/linux-raspberrypi-kernel_1.20190925-1' CC [M] /home/vbhadra/rpi/GobiNet/GobiUSBNet.o In file included from ./include/net/sock.h:58:0, from ./include/net/inet_sock.h:26, from ./include/net/ip.h:31, from /home/vbhadra/rpi/GobiNet/GobiUSBNet.c:94: ./include/linux/memcontrol.h: In function 'task_in_memcg_oom': ./include/linux/memcontrol.h:546:2: warning: return makes integer from pointer without a cast [enabled by default] /home/vbhadra/rpi/GobiNet/GobiUSBNet.c: At top level: /home/vbhadra/rpi/GobiNet/GobiUSBNet.c:112:2: warning: #warning "Remove memcontrol.h task_in_memcg_oom warning : replace 'return p->memcg_in_oom;' to 'return p->memcg_in_oom==NULL ? 0 : 1;' in function task_in_memcg_oom" [-Wcpp] /home/vbhadra/rpi/GobiNet/GobiUSBNet.c:113:2: warning: #warning "Commnet '#define MEMCG_NOT_FIX' above after fix applied." [-Wcpp] CC [M] /home/vbhadra/rpi/GobiNet/QMIDevice.o CC [M] /home/vbhadra/rpi/GobiNet/QMI.o LD [M] /home/vbhadra/rpi/GobiNet/GobiNet.o Building modules, stage 2. MODPOST 1 modules CC /home/vbhadra/rpi/GobiNet/GobiNet.mod.o LD [M] /home/vbhadra/rpi/GobiNet/GobiNet.ko make[1]: Leaving directory '/home/vbhadra/Downloads/linux-raspberrypi-kernel_1.20190925-1' Check if there is a new kernel module been compiled called GobiNet.ko (in your case your define obj-m name). In this case the driver defined module name was GobiNet in the Makefile as below: obj-m := GobiNet.o So I will check if there is a GobiNet.ko been generated: vbhadra@vbhadra-8200-elit-convertable-microtower:~/rpi/GobiNet$ ls -la GobiNet.ko -rw-r--r-- 1 vbhadra vbhadra 217987 Feb 21 11:17 GobiNet.ko Copy this .ko file in a sdcard and insert into a Pi. Copy the .ko file from the sdcard to home folder in Pi. Then do the below insert it into the Pi Kernel: pi@raspberrypi:~ $ sudo insmod GobiNet.ko pi@raspberrypi:~ $ dmesg [ 2526.062621] GobiNet: 2019-11-22/SWI_2.60 [ 2526.064306] usbcore: registered new interface driver GobiNet As you can see now the cross compiled GobiNet driver is up and running in the Pi Kernel.