--- /dev/null
+ ===========================
+ 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
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