I'm running embedded Linux (Angstrom) on an Atmel board (at91 sam9g25) mounting an ARM MCU.
I'd like to set the CPU in idle mode, ideally from userspace by using a function (then the system would be waken up by an hardware gpio interrupt). How can I do that? Alternatively, how can it be done in kernelspace?
I cannot find much, maybe somebody has some example to start from?
Try checking this page . Try also reading Optimizing Power Consumption for AT91SAM9261-based Systems to have an idea about what you can do with power management.
What you can basically do is setting the state you want in /sys/power/state but before entering the low-power state you need to set how your system can be awakened.
Be advised that, in my experience, I have seen a lot of different behaviors by changing the kernel, so by patient and try different versions.
Related
I am working on ARM Cortex-M0+. I need put CPU to a deep sleep mode to measure its standby power consumption. I use Keil uLink debugger to load the firmware. However debugger stops CPU to sleep when connecting. Is it possible to disable debugger port after I load/run the firmware? How can I do that?
It seems this function may fall in the grey area between architected functionality, device specific features, and tool capabilities.
The ARM ADIv5 debug interface certainly can request DEBUGPWRUP. When tools connect over SWD or JTAG, they have to set this before being able to make accesses. The bit won't be cleared by simply pulling the connection (there is no liveness indication on the target side). Clearing this bit using a debug toolchain (as opposed to a low-level drive) might be tricky.
Some STM32 devices seem to provide DBGMCU_Config in a the vendor-specific library to control the interaction between sleep states and debug. It's permitted to either emulate low power states (i.e. remain active, just stalled) or sleep even when debug is connected.
This level of detail is generally described in the device specific documentation from the vendor, and there may be more than one way of achieving what you need. A power-sensitive part is more likely to have an app-note on the type of measurement you're looking for.
I am trying to run a Linux kernel as the secure OS on a TrustZone enabled development board(Samsung exynos 4412). Although somebody would say secure os should be small and simple. But I just want to try. And if it is possible, then write or port a trustlet application to this secure os will be easy, especially for applications with UI(trusted UI).
I bought the development board with a runnable secure OS based on Xv6 and the normal os is Android(android version 4.2.2, kernel version 3.0.15). I have tried to replace the simple secure os with the android Linux kernel, that is, with a little assembly code ahead, such as clearing the NS bit of SCR register, directly called the Linux kernel entry(with necessary kernel tagged list passed in).
The kernel uncompressed code is executed correctly and the first C function of the kernel, start_kernel(), is also executed. Almost all the initialization functions run well except running to calibrate_delay(). This function will wait for the jiffies changed:
/* wait for "start of" clock tick */
ticks = jiffies;
while (ticks == jiffies);
I guess the reason is no clock interrupt is generated(I print logs in clock interrupt callback functions, they are never gotten in). I have checked the CPSR state before and after the local_irq_enable() function. The IRQ and FIQ bit are set correctly. I also print some logs in the Linux kernel's IRQ handler defined in the interrupt vectors table. Nothing logged.
I know there may be some differences in interrupt system between secure world and non secure world. But I can't find the differences in any documentation. Can anybody point out them? And the most important question is, as Linux is a very complicated OS, can Linux kernel run as a TrustZone secure OS?
I am a newbie in Linux kernel and ARM TrustZone. Please help me.
Running Linux as a secure world OS should be standard by default. Ie, the secure world supervisor is the most trusted and can easily transition to the other modes. The secure world is an operating concept of the ARM CPU.
Note: Just because Linux runs in the secure world, doesn't make your system secure! TrustZone and the secure world are features that you can use to make a secure system.
But I just want to try. And if it is possible, then write or port a trustlet application to this secure os will be easy, especially for applications with UI(trusted UI).
TrustZone allows partitioning of software. If you run both Linux and the trustlet application in the same layer, there is no use. The trustlet is just a normal application.
The normal mode for trustlets is to setup a monitor vector page on boot and lock down physical access. The Linux kernel can then use the smc instruction to call routines in the trustlet to access DRM type functionality to decrypt media, etc. In this mode, Linux runs as a normal world OS, but can call limited functionality with-in the secure world through the SMC API you define.
Almost all the initialization functions run well except running to calibrate_delay().
This is symptomatic of non-functioning interrupts. calibrate_delay() runs a tight loop while waiting for a tick count to increase via system timer interrupts. If you are running in the secure world, you may need to route interrupts. The register GICD_ISPENDR can be used to force an interrupt. You may use this to verify that the ARM GIC is functioning properly. Also, the kernel command line option lpj=XXXXX (where XXXX is some number) can skip this step.
Most likely some peripheral interrupt router, clock configuration or other interrupt/timer initialization is done by a boot loader in a normal system and you are missing this. Booting a new board is always difficult; even more so with TrustZone.
There is nothing technically preventing Linux from running in the Secure state of an ARM processor. But it defeats the entire purpose of TrustZone. A large, complex kernel and OS such as Linux is infeasible to formally verify to the point that it can be considered "Secure".
For further reading on that aspect, see http://www.ok-labs.com/whitepapers/sample/sel4-formal-verification-of-an-os-kernel
As for the specific problem you are facing - there should be nothing special about interrupt handling in Secure vs. Non-secure state (unless you explicitly configure it to be different). But it could be that the secure OS you have removed was performing some initial timer initializations that are now not taking place.
Also 3.0.15 is an absolutely ancient kernel - it was released 2.5 years ago, based on something released over 3 years ago.
There are several issues with what you are saying that need to be cleared up. First, are you trying to get the Secure world kernel running or the Normal world kernel? You said you wanted to run Linux in the SW and Android in the NW, but your question stated, "I have tried to replace the simple secure os with the android Linux kernel". So which kernel are you having problems with?
Second, you mentioned clearing the NS-bit. This doesn't really make sense. If the NS-bit is set, clearing it requires means that you are running in the NW already (as the bit being set would indicate), you have executed a SMC instruction, switched to Monitor mode, set the NS-bit to 0, and then restored the SW registers. Is this the case?
As far as interrupts are concerned, have you properly initialized the VBAR for each execution mode, i.e. Secure world VBAR, Normal world VBAR, and MVBAR. All three will need to be setup, in addition to setting the proper values in the NSACR and others to ensure interrupts are channeled to the correct execution world and not all just handled by the SW. Also, you do need separate exception vector tables and handlers for all three modes. You might be able to get away with only one set initially, but once you partition your memory system using the TZASC, you will need separate everything.
TZ requires a lot of configuration and is not simply handled by setting/unsetting the NS-bit. For the Exynos 4412, numerous TZ control registers that must be properly set in order to execute in the NW. Unfortunately, none of the information on them is covered in the Public version of the User's Guide. You need the full version in order to get all the values and address necessary to actually run a SW and NW kernel on this processor.
From Nvidia's website, it explain the time-out problem:
Q: What is the maximum kernel execution time? On Windows, individual
GPU program launches have a maximum run time of around 5 seconds.
Exceeding this time limit usually will cause a launch failure reported
through the CUDA driver or the CUDA runtime, but in some cases can
hang the entire machine, requiring a hard reset. This is caused by
the Windows "watchdog" timer that causes programs using the primary
graphics adapter to time out if they run longer than the maximum
allowed time.
For this reason it is recommended that CUDA is run on a GPU that is
NOT attached to a display and does not have the Windows desktop
extended onto it. In this case, the system must contain at least one
NVIDIA GPU that serves as the primary graphics adapter.
Source: https://developer.nvidia.com/cuda-faq
So it seems that, nvidia believes, or at least strongly implys, having multi- (nvidia) gpus, and with proper configuration, can prevent this from happening?
But how? so far I tried lots ways but there is still the annoying time-out on a GK110 GPU that is: (1) plugging in the secondary PCIE 16X slots; (2) Not being connected to any monitors (3) Is setted to use as an exclusive physX card in driver control panel (as recommended by some other guys), but the block-out is still there.
If your GK110 is a Tesla K20c GPU, then you should switch the device from wddm mode to TCC mode. This can be done with the nvidia-smi.exe tool that gets installed with the driver. Use the windows search function to find this file (nvidia-smi.exe) then use the command line help (`nvidia-smi --help) to discover the commands necessary to switch a GPU from WDDM to TCC mode.
Once you have done this, the windows watchdog mechanism will no longer pay attention to your GK110 device.
If on the other hand it is a GeForce GPU, there is no way to switch it to TCC mode. Your only option is to modify the registry settings, which is somewhat difficult. Your mileage may vary, as the exact structure of the reg keys varies by OS.
If a GPU is in WDDM mode, it is subject to the watchdog timer.
I'm building an IOKit CFPlugin driver for OS X. I'll be working with network data coming in that will be translated to MIDI data. No hardware is involved other than the built-in Airport. I have experience with drivers on Windows machines and firmware but this is my first dip into doing it on the Mac. So far things are going pretty well, but the Apple documentation sez: "For safety reasons, you should not load your driver on your development machine."
I only have one Mac. I really don't want two Macs- sorry, Apple. Should I take this warning seriously? Are there things I need to know?
Thanks, Tom Jeffries
You could also consider running OS X inside a VM as your testbed. It would surely be much more convenient that having a separate boot volume.
The warning is rather poorly worded; what you should consider doing is using a separate boot volume (partition) for trying out your driver, since it's possible to arbitrarily hose your system with your driver.
If you're doing kernel development on any OS that isn't isolated from your main system (via a VM, alternate boot disk, etc.), you're crazy!
What may be a bigger issue is that you can't do any kernel debugging, because the only option for that is to use GDB on a remote OS X system. For this, you may want to consider running OS X in virtualization.
you DEFINITELY want to have some way to recover a fubar kext installation: a bootable external drive or something you can quickly restore from-- this is the main reason for Apple's warning against running in-development-kernel-extensions on your production machine.
Nicholas is right that in order to debug using gdb (the only way in kernel space) you do need two machines. I've never tried using a VM as Coxy suggests: but I guess it's feasible (assuming that you run your kext on the virtual machine and use the real host machine to run gdb).
My preferred method for tracing and debugging in the kernel is kprintf() routed to firewire (aka firewire kprintf (man fwkpfv) ). for this you do need two machines with firewire ports.
finally, being an old computer musician myself, I wonder why you want to program a MIDI synthesizer (or transformer) on the network stack level. my guess is that you would have a much more gratifying experience working in userland (where you can use floating point math...)
if you need some hints or tips, feel free to get in touch...
|K<
from the ADC Kernel Programming Guide
Kernel programming is a black art that
should be avoided if at all possible.
Fortunately, kernel programming is
usually unnecessary. You can write
most software entirely in user space.
Even most device drivers (FireWire and
USB, for example) can be written as
applications, rather than as kernel
code. A few low-level drivers must be
resident in the kernel's address
space, however, and this document
might be marginally useful if you are
writing drivers that fall into this
category.
I am doing an OS experiment. Until now, all my code utilized the real mode BIOS interrupts to manipulate the hard disk and floppy. But once my code enables Protected Mode, all the real mode BIOS interrupt service routines won't be available.
I have a feeling that I need to do some hardware drivers now. Am I right? Is this why an OS is so difficult to develop?
I know that hardware is controlled by reading from and writing to certain control or data registers. For example, I know that the "Command Block Registers" of a hard disk range from 0x1F0 to 0x1F7. I am wondering whether the register addresses of so many different hardware devices are consistent on different platforms? Or do I have to detect that before using them? How would I do that?
Since I am not sure about how to read/write a floppy or a hard disk in Protected Mode, I have to use BIOS interrupts to load all my necessary kernel files from the floppy before entering protected mode. What could I do if my kernel file exceeds the real mode 1M space limit?
How do I read/write a hard disk when the CPU is in Protected Mode?
I have a feeling that I need to do some hardware drivers now. Am I right?
Strictly speaking; (and depending on your requirements) "need" may be too strong - in theory you can switch back to real mode to use BIOS functions, or use a virtual8086 monitor, or write an interpreter that interprets the firmware's instructions instead of executing them directly.
However, the BIOS is awful (designed for an "only one thing can happen at a time" environment that is completely unsuitable for modern systems where its expected that all devices are able to do useful work at the same time), and the BIOS is deprecated (replaced by UEFI), and it's hard to call something an OS when it doesn't have control over the hardware (because the firmware still has control of the hardware).
Note that if you do continue using BIOS functions; the state of various pieces of hardware (interrupt controller, PCI configuration space for various devices, any PCI bridges, timer/s, etc) has to match the expectations of the BIOS. What this means is that you will either be forced to accept huge limitations (e.g. never being able to use IO APICs, etc. properly) because it will break BIOS functions used by other pre-existing code, or you will be forced to do a huge amount of work to make the BIOS happy (emulating various pieces of hardware so the BIOS thinks the hardware is still in the state it expects even though it's not).
In other words; if you want an OS that's good then you do need to write drivers; but if you only want an OS that doesn't work on modern computers (UEFI), has severe performance problems ("only one thing can happen at a time"), is significantly harder to improve, doesn't support any devices that the BIOS doesn't support (e.g. sound cards), and doesn't support any kind of "hot-plug" (e.g. plugging in a USB device), then you don't need to write drivers.
Is this why an OS is so difficult to develop?
A bad OS is easy to develop. For example, something that is as horrible as MS-DOS (but not compatible with MS-DOS) could probably be slapped together in 1 month.
What makes an OS difficult to develop is making it good. Things like caring about security, trying to get acceptable performance, supporting multi-CPU, providing fault tolerance, trying to make it more future-proof/extensible, providing a nice GUI, creating well thought-out standards (for APIs, etc), and power management - these are what makes an OS difficult.
Device drivers add to the difficulty. Before you can write drivers you'll need support for things that drivers depend on (memory management, IRQ handling, etc - possibly including scheduler and some kind of communication); then something to auto-detect devices (e.g. to scan PCI configuration space) and try to start the drivers for whatever was detected (possibly/hopefully from file system or initial RAM disk, with the ability to add/unload/replace drivers without rebooting); and something to manage the tree of devices - e.g. so that you know which "child devices" will be effected when you put a "parent device" to sleep (or the "parent device" has hardware faults, or its driver crashes, or the device is unplugged). Of course then you'd need to write the device drivers, where the difficulty depends on the device itself (e.g. a device driver for a NVidia GPU is probably harder to write than a device driver for a RS232 serial port controller).
For storage devices themselves (assuming "80x86 PC") there's about 8 standards that matter (ATA/ATAPI, AHCI and NVMe; then OHCI, UHCI, eHCI and xHCI for USB controllers, then the USB mass storage device spec). However, there is also various RAID controllers and/or SCSI controllers where there's no standard (each of these controllers need their own driver), and some obsolete stuff (floppy controller, tape drives that plugged into floppy controller or parallel port, three proprietary CD-ROM interfaces that were built into sound cards).
Please understand that supporting all of this isn't the goal. The goal should be to provide things device drivers depend on (described above), then provide specifications that describe the device driver interfaces (possibly/hopefully including things like IO priorities and synchronization, and notifications for device/media removal, error handling, etc) so that other people can write device drivers for you. Once that's done you might implement a few specific device drivers yourself (e.g. maybe just AHCI initially - everything else could be left until much later or until someone else writes it).
You don't necessarily HAVE to write drivers. You could drop back into real mode to call the BIOS service, and then hop back into protected mode when you're done. This is essentially how DPMI DOS extenders (DOS4GW, Causeway, etc) work.
The source code for the Causeway DOS extender is public domain, you can look at that for a reference. http://www.devoresoftware.com/freesource/cwsrc.htm