Linux

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: tangrs

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: No public nightlies yet.

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

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 tty= 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.

LCD contrast/backlight

At the moment, contrast or backlight settings can be found at /proc/contrast for classic calculators and /proc/backlight for CX models 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