Linux

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This page documents the Linux port to the Nspire calculator.

Status

Classic

Hardware Possible? Implemented? Notes
CPU Yes Yes
SDRAM Yes Yes
SRAM Yes Yes
GPIO Yes Yes
UART1 Yes Yes
I2C Yes Yes
Watchdog timer Yes Yes
RTC Yes Yes
Power management Yes WIP Basic CPU frequency scaling has been implemented
Timer 1 Yes No
Timer 2 Yes Yes
Keypad Yes Yes
Touchpad Yes Yes
LCD Contrast/Backlight Yes Basic
TI-84 Link port Unknown No Do we really need this?
LED Unknown No Weird protections stop the LED from being used so there's probably no point in implementing.
SPI Yes No
USB OTG Yes Yes
USB Host Yes Yes
NAND Unknown No
LCD Yes Yes
ADC Yes Yes
DES encryption/SHA generator Yes No
Interrupt controller Yes Yes

CX

Hardware Possible? Implemented? Notes
CPU Yes Yes
SDRAM Yes Yes
SRAM Yes Yes
GPIO Yes Yes
UART1 Yes Yes
I2C Yes Yes
Watchdog timer Yes Yes
RTC Yes Yes
Power management Yes WIP Basic CPU frequency scaling has been implemented
Timer 1 Yes No
Timer 2 Yes Yes
Keypad Yes Yes
Touchpad Yes Yes
LCD Contrast/Backlight Yes Yes
TI-84 Link port Unknown No Do we really need this?
LED Unknown No Weird protections stop the LED from being used so there's probably no point in implementing.
SPI Yes No
USB OTG Yes Yes Current implementation breaks USB Host (see notes)
USB Host Yes USB 1.1 Uses a workaround but limits speed to USB 1.1
NAND Yes WIP Needs a lot of testing. Unstable.
LCD Yes Yes
ADC Yes Yes
DES encryption/SHA generator Yes No
Interrupt controller Yes Yes

Booting

To have something useful running using Linux on the calculator, a bootloader, kernel and rootfs is needed.

Bootloader

Source code: On github

Nightly builds: None.

Binary: TI-Planet

The bootloader is run from the Nspire OS to load everything into memory and execute the kernel.

Usage instructions can be found in the readme 

 Copy linuxloader.tns to your calculator and run it.
 
 Valid commands are:
 
     kernel <filename>: Loads a kernel image into memory
     initrd <filename>: Loads a ramdisk into memory
     dump: Prints out the current internal state of the bootloader. Useful for
 debugging.
     free: Prints out the total amount of memory provided to the bootloader by
 the Nspire OS and amounts used by the kernel and ramdisks.
     cmdline [str]: Get/set the kernel command line parameters.
     mach [id]: Get/set the machine ID that will be provided to Linux upon
 booting. Useful for overriding the builtin default value without having to
 recompile.
     phys [<start> <size>]: Get/set the address and size of physical memory.
 Useful for overriding the builtin default value without having to recompile.
     rdsize [size]: Get/set the size of the ramdisk that Linux should create on
 boot. Leave at 0x0 for the kernel default.
     probemem: If this is run on an calculator model that isn't directly
 supported by the bootloader, you can use this to try and guess how much memory
 the system has.
     poke <addr> <value>: Write a word to an arbitrary location in the memory
 address space.
     peek <addr>: Read a word from an arbitrary location in the memory address
 space.
     boot: Boot kernel.
 
 The bootloader is also scriptable. Create a text file containing a list of
 commands to be executed and change the extension to .ll2.tns, and add the
 following line to your /documents/ndless/ndless.cfg.tns file.
 
 ext.ll2=linuxloader2
 
 Then simply open your script file and the loader will execute all the commands
 in it. A sample one could look like this:
 
 kernel linux/zImage.tns
 initrd linux/initrd.tns
 cmdline root=/dev/ram
 boot
 
 This should save a lot of typing everytime you need to boot Linux.

Kernel

Source code: On github

Nightly builds: TI-Planet (WIP)

To compile the kernel with default options, first clone the github repo then run: 

 export ARCH=arm
 make nspire_defconfig
 make -j
 cp arch/arm/boot/zImage /path/to/folder/zImage.tns

Rootfs

Nightly builds: TI-Planet (WIP)

To have programs actually run on the kernel, you need a root filesystem of some sort containing the userspace programs.

For testing and mucking around, a initrd should be enough. It is possible to build one using Buildroot or look around the Omnimaga thread for a pre-built one.

For a larger root filesystem, you could put a filesystem on a USB drive and add root=/dev/sdaX to your kernel command line. You may also need to add rootdelay=10 to give the USB drive time to initialize.

Quirks and technical details

SRAM

When needing to allocate memory from SRAM when developing for the kernel, use the following functions: 

 void *sram_alloc(unsigned int size, dma_addr_t *dma_addr)
 void sram_free(dma_addr_t addr, unsigned int size)

UART

Add ,115200n8 to the end of your console= command line options to keep it the same as the Nspire OS.

Keypad

The keymaps can be found in arch/arm/mach-nspire/keypad.c. Each array element represents one bit in Keypads.

Touchpad

There are some weird issues with the Touchpad. After booting Linux, the Touchpad doesn't function correctly under Nspire OS and requires entering diags or a few hard resets to get it back to normal. The exact cause is unknown but it is possible that this behavior is caused by the bootloader not correctly resetting Touchpad controller when the device boots up again so the Nspire OS is still using a Linux-configured Touchpad controller.

It has been half solved by having the Touchpad driver reset the controller on a soft reboot. However, this doesn't happen on hard reboots and will still cause the Nspire OS to not function correctly. Whenever possible, perform a soft reboot in Nspire Linux by using Ctrl+Alt(Var)+Delete(Scratchpad) or using the reboot command.

LCD contrast/backlight

At the moment, contrast settings can be found at /proc/contrast for classic calculators though this will be deprecated soon. The CX already has a working driver for backlight control.

LED

The LED has some hardware protections put on by the Nspire OS. Currently, nobody knows how to bypass this protection and we can't use it. Therefore, there's probably no reason to integrate support into the kernel.

USB

USB support is mostly working. The only thing missing is a USB PHY driver. The USB controller driver is currently unable to switch seamlessly between USB host and USB device mode because of this. Unfortunately, nothing much is known about the USB PHY.

That's probably the same reason why sometimes USB devices aren't recognised in USB host mode - the USB PHY hasn't changed the USB hardware to host mode.

To work around this, we get the Nspire OS to set the right modes in the USB PHY before booting Linux.

For USB Host mode: insert a USB OTG cable's A end or a USB device into the calculator while still inside the Nspire OS before running the bootloader.

For USB Device mode: connect the Nspire to a computer while in Nspire OS before running the bootloader.

The USB hardware on the calculators also provide very little power (something in the double digit milliamps). For anything other than a basic USB drive or a keyboard, a powered USB hub might be required to supply enough power.

Extra notes for CX

Both OTG and USB host work on the CX but since it needs a workaround that can't be integrated into the OTG driver, only one will work at a time. To maintain compatibility, the default is to use the USB host only driver. If you wish to use USB OTG on the CX, simply add cx_usb_otg to your kernel command line arguments.

USB PHY developer notes

It seems the only thing the OS does when switching is changing output in some of the GPIO registers. This needs further investigation.

ADC

ADC values can be read at /sys/bus/iio/devices/iio:device0 (310 = 1V).

More information

Omnimaga thread FAQ

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