Address types used in Linux The following is a list of address types used in Linux. Figure 13-1 shows how these address types relate to physical memory. User virtual addresses These are the regular addresses seen by user-space programs. User addresses are either 32 or 64 bits in length, depending on the underlying hardware architecture, and each process has its own virtual address space. Physical addresses The addresses used between make the processor and the system's memory. Physical addresses are 32- or 64-bit quantities; even 32-bit systems can use 64-bit physical addresses in some situations. Bus addresses The addresses used between peripheral buses and memory. Often they are the same as the physical addresses used by the processor, but that is not necessarily the case. Bus addresses are highly architecture dependent, of course.
Address Types, linux is, of course, a virtual memory system, meaning that the addresses seen by user programs do not directly correspond to the physical addresses used by the hardware. Virtual memory introduces a layer of indirection, which allows a number of nice things. With virtual memory, programs running on the system can allocate far more memory than is physically available; indeed, even a single process can have a virtual address space larger than the system's physical memory. Virtual memory also allows playing a number of tricks with the process's address space, including mapping in device memory. Thus far, we have talked about virtual and physical addresses, but a number of the details have been glossed over. The linux system deals with several types of addresses, each with its own semantics. Unfortunately, the kernel code is not always very clear on exactly which type of address is being used in each situation, so the programmer must be careful.
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The material in this chapter is somewhat advanced, and not everybody will need a grasp. Nonetheless, many tasks can only be done through digging more deeply into the memory management subsystem; it also provides an interesting look into how an important part of kannada the kernel works. The material in this chapter is divided into three sections. The first covers the implementation of the mmap system call, which allows the mapping of device memory directly into a user process's address space. We then cover the kernel kiobuf mechanism, which provides direct access to user memory from kernel space. The kiobuf system may be used to implement "raw I/O for certain kinds of devices.
The final section covers direct memory access (DMA) I/O operations, which essentially provide peripherals with direct access to system memory. Of course, all of these techniques require an understanding of how. Linux memory management works, so we start with an overview of that subsystem. Rather than describing the theory of memory management in operating grading systems, this section tries to pinpoint the main features of the linux implementation of the theory. Although you do not need to be a linux virtual memory guru to implement mmap, a basic overview of how things work is useful. What follows is a fairly lengthy description of the data structures used by the kernel to manage memory. Once the necessary background has been covered, we can get into working with these structures.
0.145 boot1 version :.3.1a.145 pmu type.1.176 axi:ahb:apb3:2:2.176 set dcdc21400, clock1008 successed.178 key.486 you can unclench the key to update now.486 key found, jump to fel Common Pitfalls It failed! Try again, make sure you fully power down the device and make sure you get the order of events right. Reading over usb fails If the following happens:./sunxi-fel read 0x x20000 n libusb usb_bulk_send error -7 Then you probably are trying to read things that only get initialized when boot0 and boot1 have been loaded. Try another method of entering fel mode, one that does initialize to boot1. The fel is actually a tiny usb stack implementing a special usb protocol. Part of it is implemented in our tools repository and can be used as reference code.
If you get usb_bulk_send error -7 after some command it means soc/fel stack left fel mode or crashed. You either booted something or hung the device you can reset via fel by enabling watchdog:./sunxi-fel writel 0x01c20c94 3 Or, if in u-boot, use: mw 0x01c20c94 3 ; ; ; ; This will go back to fel mode regardless if the device's fel mode jumper/button is in place. Note that a couple of blank lines are needed after the mw for some reason. There are exceptions to this rule, where boards might require you to connect to specific ports and/or use non-standard cables. Most notably is the pine64. Chapter 13 mmap and dma, contents: Memory management in Linux, the mmap device Operation. The kiobuf Interface, direct Memory Access and Bus Mastering. Backward Compatibility, quick reference, this chapter delves into the area of Linux memory management, with an emphasis on techniques that are useful to the device driver writer.
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Just install it on an sdcard as you would with the u-boot spl ( be sure to change /dev/sdX to where your sdcard is wget nxi dd nxi of/dev/sdX bs1024 seek8 by having no valid boot image If the brom doesn't find any valid boot. Thus for most devices that don't feature onboard nand world or emmc, this should apply when you simply remove the sd/µSD card. Verifying fel mode a new usb device appears When you run lsusb, you should see the following in it: Bus 001 device 074: id 1f3a:efe8 Running the sunxi-fel tool./sunxi-fel version awusbfex soc00162500(A13) ver scratchpad00007e serial output If the method you chose initialized boot1, then you. Boot0 version :.3.0 dram size 1024 Succeed in opening nand flash. Succeed in reading boot1 file head. The size of boot1 is 0x00036000. The file stored in 0X00000000 of block 2 is perfect. Ready to disable icache. Succeed in loading boot1.
With later socs, Allwinner's U-boot supports the "efex" command. If "efex" is not available in your U-boot, you can use the simple uboot "go" command with arguments pointing to the return fel address: go 0xffff0020, starting application at 0xffff0020. Entering this command at the u-boot prompt will enter into fel mode. Note: This is just an alternative way of water entering fel mode. Fel itself can/will not talk over the serial connection! In other words: you still have to connect a usb cable to make actual use of fel and associated tools. Through a special sd card image Included in our sunxi-tools repository, there is a small sdcard boot image that does nothing more than jump to fel.
for about 2 seconds. Release the power key, and press it at least 3 times immediately. Boot1 is initialized using this method. Through serial console, if you have access to the. Uart already, you can send the character '1' 2' on some devices) to the device during power-up.
Some do low-level initialization (load boot0 and boot1 and some don't. If you are going to use fel mode to retrieve device information, you need a to pick a method of entering fel mode that initializes boot1. Power off your device, before you try to enter fel mode, make sure that your device is truly powered interests off. Do not leave any cables attached. Due to a common design flaw, (current leaking from) the. Uart will often keep the device in a slightly working state. So before you power up your device again: disconnect your uart, and re-attach. Triggering fel mode, through a special fel button, this is either called recovery or uboot or fel. If your device features such a button, you just need to hold it during power-up, and the device should have entered fel mode just fine.
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Fel is a low-level subroutine contained in the. Bootrom on Allwinner devices. It is used for initial programming and recovery tree of devices using usb. Your device therefore needs to be attached to a host (your PC) by means. Usb cable, connected to a port where the sunxi device will present itself as a usb 'slave' (i.e. Usually that means the "OTG" connector. 1, our tools repository has some tools for dealing with fel mode. If you haven't done so already, retrieve the repository and build. While there are a few different ways to trigger fel mode, they are not always equal.