So Techy ...

Wednesday, December 2, 2015

Linux Memory Management

32 bit : http://tldp.org/HOWTO/KernelAnalysis-HOWTO-7.html
64 bit : https://www.kernel.org/doc/gorman/html/understand/understand012.html

Check Memory Utilization
cat /proc/meminfo
free -m

Configuration
/proc/sys/vm/*

Dirty Page
/proc/sys/vm/dirty_background_ratio: disk write buffer flushing threshold as percentage of system memory
/proc/sys/vm/dirty_ratio: disk write buffer size as percentage of system memory

Handle out of memory
/proc/sys/vm/vfs_cache_pressure
/proc/sys/vm/min_free_kbytes
/proc/sys/vm/drop_cache

Friday, November 20, 2015

Warp!! Linux/Android fast boot

http://www.lineo.co.jp/modules/products/warp2.html

Thursday, November 19, 2015

Issue SATA commands directly through IOCTL

Directly write to SATA interface to perform simple read and write operation on a storage device.

#include <scsi/sg.h>
#include <scsi/scsi.h>
main()
{
 int fd;
 unsigned char buffer[512];

 fd=open("/dev/sda", O_RDWR );

 ReadSector(fd, 0, 1, buffer);
 WriteSector(fd, 0, 1, buffer);
}


// return 0 on fail
// return 1 on success
int ReadSector(int fd, int sector, int nsec, unsigned char *pbuffer)
{
 int res;
 int t_length;
 sg_io_hdr_t io_hdr;
 unsigned char sense_b[SG_MAX_SENSE];
 unsigned char rdCmdBlk6[6];

 t_length = 512;              // 512 bytes transferred per sec

// Prepare SCSI READ (6) command
 rdCmdBlk6[0]  = READ_6;           // COMMAND
 rdCmdBlk6[1]  = (sector & 0xFF0000 ) >> 16;           // LBA
 rdCmdBlk6[2]  = (sector & 0xff00) >> 8;         // LBA
 rdCmdBlk6[3]  = sector & 0xff;  // LBA
 rdCmdBlk6[4]  = nsec;
 rdCmdBlk6[5]  = 0x00;

// Prepare the sg_io_hdr_t structure
 memset(&io_hdr, 0, sizeof(sg_io_hdr_t));
 io_hdr.interface_id = 'S';                  // Always set to 'S' for sg driver
 io_hdr.cmd_len = sizeof(rdCmdBlk6);         // Size of SCSI command
 io_hdr.mx_sb_len  = sizeof(sense_b);        // Max sense buffer size(for error)
 io_hdr.dxfer_direction = SG_DXFER_FROM_DEV; // Data transfer direction(no data)
 io_hdr.dxfer_len = nsec*t_length;                // Data transfer length(512)
 io_hdr.dxferp = pbuffer;                       // Data transfer buffer(none)
 io_hdr.cmdp = rdCmdBlk6;                    // SCSI command buffer
 io_hdr.sbp = sense_b;                       // Sense buffer
 io_hdr.timeout = 5000;                      // Timeout(5s)

// Sends the command to device
 if ((res = ioctl(fd, SG_IO, &io_hdr)) < 0) {
   return 0;
 }

// Error processing
 if ( ((io_hdr.info & SG_INFO_OK_MASK) != SG_INFO_OK) || // check info
      (io_hdr.masked_status != 0x00) ||                  // check status(0 if ioctl success)
      (io_hdr.msg_status != 0x00) ||                     // check message status
      (io_hdr.host_status != 0x00) ||                    // check host status
      (io_hdr.driver_status != 0x00) )                   // check driver status
 {
   return 0;
 } else {
   return 1;
 }
}

int WriteSector(int fd, int sector, int nsec, unsigned char *pbuffer)
{
 int res;
 int t_length;
 sg_io_hdr_t io_hdr;
 unsigned char sense_b[SG_MAX_SENSE];
 unsigned char rdCmdBlk6[6] ;
 t_length = 512;              // 512 bytes transferred per sec

// Prepare SCSI WRITE (6) command
 rdCmdBlk6[0]  = WRITE_6;           // COMMAND
 rdCmdBlk6[1]  = (sector & 0xFF0000 ) >> 16;           // LBA
 rdCmdBlk6[2]  = (sector & 0xff00) >> 8;         // LBA
 rdCmdBlk6[3]  = sector & 0xff;  // LBA
 rdCmdBlk6[4]  = nsec;
 rdCmdBlk6[5]  = 0x00;

// Prepare the sg_io_hdr_t structure
 memset(&io_hdr, 0, sizeof(sg_io_hdr_t));
 io_hdr.interface_id = 'S';                  // Always set to 'S' for sg driver
 io_hdr.cmd_len = sizeof(rdCmdBlk6);         // Size of SCSI command
 io_hdr.mx_sb_len  = sizeof(sense_b);        // Max sense buffer size(for error)
 io_hdr.dxfer_direction = SG_DXFER_TO_DEV; // Data transfer direction(no data)
 io_hdr.dxfer_len = nsec*t_length;                // Data transfer length(512)
 io_hdr.dxferp = pbuffer;                       // Data transfer buffer(none)
 io_hdr.cmdp = rdCmdBlk6;                    // SCSI command buffer
 io_hdr.sbp = sense_b;                       // Sense buffer
 io_hdr.timeout = 5000;                      // Timeout(5s)

// Sends the command to device
 if ((res = ioctl(fd, SG_IO, &io_hdr)) < 0) {
   return 0;
 }

// Error processing
 if ( ((io_hdr.info & SG_INFO_OK_MASK) != SG_INFO_OK) || // check info
      (io_hdr.masked_status != 0x00) ||                  // check status(0 if ioctl success)
      (io_hdr.msg_status != 0x00) ||                     // check message status
      (io_hdr.host_status != 0x00) ||                    // check host status
      (io_hdr.driver_status != 0x00) )                   // check driver status
 {
   return 0;
 } else {
   return 1;
 }
}

Tuesday, November 17, 2015

Intel xHCI drivers

xHCI

https://downloadcenter.intel.com/download/21129/USB-3-0-Driver-Intel-USB-3-0-eXtensible-Host-Controller-Driver-for-Intel-7-Series-C216-Chipset-Family

https://downloadcenter.intel.com/download/22824/USB-3-0-Driver-Intel-USB-3-0-eXtensible-Host-Controller-Driver-for-Intel-8-9-100-Series-and-C220-C610-Chipset-Family

CentOS 7 32 bit VirtualBox client

Officially, CentOS 7 only has x86_64. The first version 7.0 was released in 2014.

Not until 10/13/2015, AltArch SIG released a CentOS 7 32 bit for IOT x86 boards.
Release note: https://wiki.centos.org/SpecialInterestGroup/AltArch/i386
Release images: http://mirror.centos.org/altarch/7/isos/i386/

Not like the x86_64 version, the 32 bit version is not typically available on CentOS mirror sites.

At this moment, AltArch CentOS 7 32 bit version meets our need of creating USB token now with a catch.
- The two required RPM packages are from CentOS 6.7. Luckily, they are working.

So far, I believe that it would be in the best interests of normal institution to consider taking CentOS 7 x86_64 instead of 32bit (i386/i686) version. With x86_64, there is definitely less worry for future.

Note for getting the task done.

2 VirtualBox
2.1 Required VirtualBox components
Both VirtualBox installer and extension pack are required. They can be found on the URL
http://www.oracle.com/technetwork/server-storage/virtualbox/downloads/index.html

2.2 Virtual Machine Creation
2.2.1 VirtualBox options
System->Motherboard->Base Memory must be >= 512MB
System->Processor->Extended Features check Enable PAE/NX
Network->Adapter 1 -> Advanced ->Adapter Type Intel PRO/1000 MT Desktop (8254OEM)
USB -> Enable USB Controller -> USB 3.0 (xHCI) Controller

Note that xHCI driver should be from vendors, Intel etc.

3 Install CentOS
3.1 Required CentOS 7 components
CentOS 7 ISO image
http://mirror.centos.org/altarch/7/isos/i386/CentOS-7-i386-Minimal-1503.iso
vim filesystem RPM package
ftp://fr2.rpmfind.net/linux/centos/6.7/os/i386/Packages/vim-filesystem-7.4.629-5.el6.i686.rpm
vim common RPM package
ftp://fr2.rpmfind.net/linux/centos/6.7/os/i386/Packages/vim-common-7.4.629-5.el6.i686.rpm

Friday, November 13, 2015

CentOS 7 32 bit virtualbox client

32bit CentOS 7 was released on 10/15/2015

The download is available here
http://mirror.centos.org/altarch/7/isos/i386/

When creating virtualbox client, the default configurations are not sufficient.

Create Virtual Machine:
- Linex and Other Linux(32-bit)

Settings
- System->Processor->Enable PAE/NX
- Network->Advanced->Adapter Type: Intel PRO/1000 MT Desktop (8254OEM)

CentOS 7 i386 by default won't recognize the default virtualbox network device. This is from the 3.10 kernel taken by CentOS 7
https://www.centos.org/forums/viewtopic.php?f=47&t=47724

For development on CentOS, the following line will install compiler/linker packages.
yum groupinstall 'Development Tools'

Monday, November 2, 2015

Magic Leap: 3D Displays using Scanning Laser Projection

Magic Leap Inc.

News:
http://www.forbes.com/sites/theopriestley/2015/10/24/why-magic-leap-needs-a-dose-of-reality-to-succeed/

In Depth:
http://gizmodo.com/how-magic-leap-is-secretly-creating-a-new-alternate-rea-1660441103

Paper:
https://drive.google.com/open?id=0B11ZqB11tZ92ZVpWV185N2JvcVU

Patent
http://www.google.com/patents/WO2014113506A1?cl=en