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).