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Diffstat (limited to 'Documentation/frv/features.txt')
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diff --git a/Documentation/frv/features.txt b/Documentation/frv/features.txt new file mode 100644 index 00000000000..fa20c0e7283 --- /dev/null +++ b/Documentation/frv/features.txt @@ -0,0 +1,310 @@ + =========================== + 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 |