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