311 lines
11 KiB
Plaintext
311 lines
11 KiB
Plaintext
===========================
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FUJITSU FR-V LINUX FEATURES
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===========================
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This kernel port has a number of features of which the user should be aware:
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(*) Linux and uClinux
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The FR-V architecture port supports both normal MMU linux and uClinux out
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of the same sources.
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(*) CPU support
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Support for the FR401, FR403, FR405, FR451 and FR555 CPUs should work with
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the same uClinux kernel configuration.
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In normal (MMU) Linux mode, only the FR451 CPU will work as that is the
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only one with a suitably featured CPU.
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The kernel is written and compiled with the assumption that only the
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bottom 32 GR registers and no FR registers will be used by the kernel
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itself, however all extra userspace registers will be saved on context
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switch. Note that since most CPUs can't support lazy switching, no attempt
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is made to do lazy register saving where that would be possible (FR555
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only currently).
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(*) Board support
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The board on which the kernel will run can be configured on the "Processor
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type and features" configuration tab.
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Set the System to "MB93093-PDK" to boot from the MB93093 (FR403) PDK.
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Set the System to "MB93091-VDK" to boot from the CB11, CB30, CB41, CB60,
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CB70 or CB451 VDK boards. Set the Motherboard setting to "MB93090-MB00" to
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boot with the standard ATA90590B VDK motherboard, and set it to "None" to
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boot without any motherboard.
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(*) Binary Formats
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The only userspace binary format supported is FDPIC ELF. Normal ELF, FLAT
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and AOUT binaries are not supported for this architecture.
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FDPIC ELF supports shared library and program interpreter facilities.
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(*) Scheduler Speed
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The kernel scheduler runs at 100Hz irrespective of the clock speed on this
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architecture. This value is set in asm/param.h (see the HZ macro defined
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there).
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(*) Normal (MMU) Linux Memory Layout.
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See mmu-layout.txt in this directory for a description of the normal linux
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memory layout
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See include/asm-frv/mem-layout.h for constants pertaining to the memory
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layout.
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See include/asm-frv/mb-regs.h for the constants pertaining to the I/O bus
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controller configuration.
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(*) uClinux Memory Layout
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The memory layout used by the uClinux kernel is as follows:
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0x00000000 - 0x00000FFF Null pointer catch page
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0x20000000 - 0x200FFFFF CS2# [PDK] FPGA
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0xC0000000 - 0xCFFFFFFF SDRAM
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0xC0000000 Base of Linux kernel image
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0xE0000000 - 0xEFFFFFFF CS2# [VDK] SLBUS/PCI window
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0xF0000000 - 0xF0FFFFFF CS5# MB93493 CSC area (DAV daughter board)
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0xF1000000 - 0xF1FFFFFF CS7# [CB70/CB451] CPU-card PCMCIA port space
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0xFC000000 - 0xFC0FFFFF CS1# [VDK] MB86943 config space
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0xFC100000 - 0xFC1FFFFF CS6# [CB70/CB451] CPU-card DM9000 NIC space
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0xFC100000 - 0xFC1FFFFF CS6# [PDK] AX88796 NIC space
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0xFC200000 - 0xFC2FFFFF CS3# MB93493 CSR area (DAV daughter board)
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0xFD000000 - 0xFDFFFFFF CS4# [CB70/CB451] CPU-card extra flash space
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0xFE000000 - 0xFEFFFFFF Internal CPU peripherals
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0xFF000000 - 0xFF1FFFFF CS0# Flash 1
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0xFF200000 - 0xFF3FFFFF CS0# Flash 2
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0xFFC00000 - 0xFFC0001F CS0# [VDK] FPGA
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The kernel reads the size of the SDRAM from the memory bus controller
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registers by default.
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The kernel initialisation code (1) adjusts the SDRAM base addresses to
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move the SDRAM to desired address, (2) moves the kernel image down to the
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bottom of SDRAM, (3) adjusts the bus controller registers to move I/O
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windows, and (4) rearranges the protection registers to protect all of
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this.
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The reasons for doing this are: (1) the page at address 0 should be
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inaccessible so that NULL pointer errors can be caught; and (2) the bottom
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three quarters are left unoccupied so that an FR-V CPU with an MMU can use
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it for virtual userspace mappings.
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See include/asm-frv/mem-layout.h for constants pertaining to the memory
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layout.
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See include/asm-frv/mb-regs.h for the constants pertaining to the I/O bus
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controller configuration.
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(*) uClinux Memory Protection
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A DAMPR register is used to cover the entire region used for I/O
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(0xE0000000 - 0xFFFFFFFF). This permits the kernel to make uncached
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accesses to this region. Userspace is not permitted to access it.
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The DAMPR/IAMPR protection registers not in use for any other purpose are
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tiled over the top of the SDRAM such that:
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(1) The core kernel image is covered by as small a tile as possible
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granting only the kernel access to the underlying data, whilst
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making sure no SDRAM is actually made unavailable by this approach.
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(2) All other tiles are arranged to permit userspace access to the rest
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of the SDRAM.
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Barring point (1), there is nothing to protect kernel data against
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userspace damage - but this is uClinux.
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(*) Exceptions and Fixups
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Since the FR40x and FR55x CPUs that do not have full MMUs generate
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imprecise data error exceptions, there are currently no automatic fixup
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services available in uClinux. This includes misaligned memory access
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fixups.
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Userspace EFAULT errors can be trapped by issuing a MEMBAR instruction and
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forcing the fault to happen there.
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On the FR451, however, data exceptions are mostly precise, and so
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exception fixup handling is implemented as normal.
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(*) Userspace Breakpoints
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The ptrace() system call supports the following userspace debugging
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features:
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(1) Hardware assisted single step.
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(2) Breakpoint via the FR-V "BREAK" instruction.
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(3) Breakpoint via the FR-V "TIRA GR0, #1" instruction.
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(4) Syscall entry/exit trap.
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Each of the above generates a SIGTRAP.
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(*) On-Chip Serial Ports
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The FR-V on-chip serial ports are made available as ttyS0 and ttyS1. Note
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that if the GDB stub is compiled in, ttyS1 will not actually be available
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as it will be being used for the GDB stub.
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These ports can be made by:
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mknod /dev/ttyS0 c 4 64
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mknod /dev/ttyS1 c 4 65
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(*) Maskable Interrupts
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Level 15 (Non-maskable) interrupts are dealt with by the GDB stub if
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present, and cause a panic if not. If the GDB stub is present, ttyS1's
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interrupts are rated at level 15.
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All other interrupts are distributed over the set of available priorities
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so that no IRQs are shared where possible. The arch interrupt handling
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routines attempt to disentangle the various sources available through the
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CPU's own multiplexor, and those on off-CPU peripherals.
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(*) Accessing PCI Devices
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Where PCI is available, care must be taken when dealing with drivers that
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access PCI devices. PCI devices present their data in little-endian form,
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but the CPU sees it in big-endian form. The macros in asm/io.h try to get
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this right, but may not under all circumstances...
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(*) Ax88796 Ethernet Driver
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The MB93093 PDK board has an Ax88796 ethernet chipset (an NE2000 clone). A
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driver has been written to deal specifically with this. The driver
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provides MII services for the card.
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The driver can be configured by running make xconfig, and going to:
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(*) Network device support
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- turn on "Network device support"
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(*) Ethernet (10 or 100Mbit)
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- turn on "Ethernet (10 or 100Mbit)"
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- turn on "AX88796 NE2000 compatible chipset"
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The driver can be found in:
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drivers/net/ax88796.c
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include/asm/ax88796.h
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(*) WorkRAM Driver
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This driver provides a character device that permits access to the WorkRAM
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that can be found on the FR451 CPU. Each page is accessible through a
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separate minor number, thereby permitting each page to have its own
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filesystem permissions set on the device file.
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The device files should be:
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mknod /dev/frv/workram0 c 240 0
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mknod /dev/frv/workram1 c 240 1
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mknod /dev/frv/workram2 c 240 2
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...
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The driver will not permit the opening of any device file that does not
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correspond to at least a partial page of WorkRAM. So the first device file
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is the only one available on the FR451. If any other CPU is detected, none
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of the devices will be openable.
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The devices can be accessed with read, write and llseek, and can also be
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mmapped. If they're mmapped, they will only map at the appropriate
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0x7e8nnnnn address on linux and at the 0xfe8nnnnn address on uClinux. If
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MAP_FIXED is not specified, the appropriate address will be chosen anyway.
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The mappings must be MAP_SHARED not MAP_PRIVATE, and must not be
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PROT_EXEC. They must also start at file offset 0, and must not be longer
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than one page in size.
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This driver can be configured by running make xconfig, and going to:
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(*) Character devices
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- turn on "Fujitsu FR-V CPU WorkRAM support"
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(*) Dynamic data cache write mode changing
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It is possible to view and to change the data cache's write mode through
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the /proc/sys/frv/cache-mode file while the kernel is running. There are
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two modes available:
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NAME MEANING
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===== ==========================================
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wthru Data cache is in Write-Through mode
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wback Data cache is in Write-Back/Copy-Back mode
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To read the cache mode:
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# cat /proc/sys/frv/cache-mode
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wthru
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To change the cache mode:
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# echo wback >/proc/sys/frv/cache-mode
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# cat /proc/sys/frv/cache-mode
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wback
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(*) MMU Context IDs and Pinning
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On MMU Linux the CPU supports the concept of a context ID in its MMU to
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make it more efficient (TLB entries are labelled with a context ID to link
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them to specific tasks).
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Normally once a context ID is allocated, it will remain affixed to a task
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or CLONE_VM'd group of tasks for as long as it exists. However, since the
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kernel is capable of supporting more tasks than there are possible ID
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numbers, the kernel will pass context IDs from one task to another if
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there are insufficient available.
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The context ID currently in use by a task can be viewed in /proc:
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# grep CXNR /proc/1/status
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CXNR: 1
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Note that kernel threads do not have a userspace context, and so will not
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show a CXNR entry in that file.
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Under some circumstances, however, it is desirable to pin a context ID on
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a process such that the kernel won't pass it on. This can be done by
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writing the process ID of the target process to a special file:
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# echo 17 >/proc/sys/frv/pin-cxnr
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Reading from the file will then show the context ID pinned.
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# cat /proc/sys/frv/pin-cxnr
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4
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The context ID will remain pinned as long as any process is using that
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context, i.e.: when the all the subscribing processes have exited or
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exec'd; or when an unpinning request happens:
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# echo 0 >/proc/sys/frv/pin-cxnr
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When there isn't a pinned context, the file shows -1:
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# cat /proc/sys/frv/pin-cxnr
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-1
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