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1da177e4 LT |
1 | =========================== |
2 | FUJITSU FR-V LINUX FEATURES | |
3 | =========================== | |
4 | ||
5 | This kernel port has a number of features of which the user should be aware: | |
6 | ||
7 | (*) Linux and uClinux | |
8 | ||
9 | The FR-V architecture port supports both normal MMU linux and uClinux out | |
10 | of the same sources. | |
11 | ||
12 | ||
13 | (*) CPU support | |
14 | ||
15 | Support for the FR401, FR403, FR405, FR451 and FR555 CPUs should work with | |
16 | the same uClinux kernel configuration. | |
17 | ||
18 | In normal (MMU) Linux mode, only the FR451 CPU will work as that is the | |
19 | only one with a suitably featured CPU. | |
20 | ||
21 | The kernel is written and compiled with the assumption that only the | |
22 | bottom 32 GR registers and no FR registers will be used by the kernel | |
23 | itself, however all extra userspace registers will be saved on context | |
24 | switch. Note that since most CPUs can't support lazy switching, no attempt | |
25 | is made to do lazy register saving where that would be possible (FR555 | |
26 | only currently). | |
27 | ||
28 | ||
29 | (*) Board support | |
30 | ||
31 | The board on which the kernel will run can be configured on the "Processor | |
32 | type and features" configuration tab. | |
33 | ||
34 | Set the System to "MB93093-PDK" to boot from the MB93093 (FR403) PDK. | |
35 | ||
36 | Set the System to "MB93091-VDK" to boot from the CB11, CB30, CB41, CB60, | |
37 | CB70 or CB451 VDK boards. Set the Motherboard setting to "MB93090-MB00" to | |
38 | boot with the standard ATA90590B VDK motherboard, and set it to "None" to | |
39 | boot without any motherboard. | |
40 | ||
41 | ||
42 | (*) Binary Formats | |
43 | ||
44 | The only userspace binary format supported is FDPIC ELF. Normal ELF, FLAT | |
45 | and AOUT binaries are not supported for this architecture. | |
46 | ||
47 | FDPIC ELF supports shared library and program interpreter facilities. | |
48 | ||
49 | ||
50 | (*) Scheduler Speed | |
51 | ||
52 | The kernel scheduler runs at 100Hz irrespective of the clock speed on this | |
53 | architecture. This value is set in asm/param.h (see the HZ macro defined | |
54 | there). | |
55 | ||
56 | ||
57 | (*) Normal (MMU) Linux Memory Layout. | |
58 | ||
59 | See mmu-layout.txt in this directory for a description of the normal linux | |
60 | memory layout | |
61 | ||
62 | See include/asm-frv/mem-layout.h for constants pertaining to the memory | |
63 | layout. | |
64 | ||
65 | See include/asm-frv/mb-regs.h for the constants pertaining to the I/O bus | |
66 | controller configuration. | |
67 | ||
68 | ||
69 | (*) uClinux Memory Layout | |
70 | ||
71 | The memory layout used by the uClinux kernel is as follows: | |
72 | ||
73 | 0x00000000 - 0x00000FFF Null pointer catch page | |
74 | 0x20000000 - 0x200FFFFF CS2# [PDK] FPGA | |
75 | 0xC0000000 - 0xCFFFFFFF SDRAM | |
76 | 0xC0000000 Base of Linux kernel image | |
77 | 0xE0000000 - 0xEFFFFFFF CS2# [VDK] SLBUS/PCI window | |
78 | 0xF0000000 - 0xF0FFFFFF CS5# MB93493 CSC area (DAV daughter board) | |
79 | 0xF1000000 - 0xF1FFFFFF CS7# [CB70/CB451] CPU-card PCMCIA port space | |
80 | 0xFC000000 - 0xFC0FFFFF CS1# [VDK] MB86943 config space | |
81 | 0xFC100000 - 0xFC1FFFFF CS6# [CB70/CB451] CPU-card DM9000 NIC space | |
82 | 0xFC100000 - 0xFC1FFFFF CS6# [PDK] AX88796 NIC space | |
83 | 0xFC200000 - 0xFC2FFFFF CS3# MB93493 CSR area (DAV daughter board) | |
84 | 0xFD000000 - 0xFDFFFFFF CS4# [CB70/CB451] CPU-card extra flash space | |
85 | 0xFE000000 - 0xFEFFFFFF Internal CPU peripherals | |
86 | 0xFF000000 - 0xFF1FFFFF CS0# Flash 1 | |
87 | 0xFF200000 - 0xFF3FFFFF CS0# Flash 2 | |
88 | 0xFFC00000 - 0xFFC0001F CS0# [VDK] FPGA | |
89 | ||
90 | The kernel reads the size of the SDRAM from the memory bus controller | |
91 | registers by default. | |
92 | ||
93 | The kernel initialisation code (1) adjusts the SDRAM base addresses to | |
94 | move the SDRAM to desired address, (2) moves the kernel image down to the | |
95 | bottom of SDRAM, (3) adjusts the bus controller registers to move I/O | |
96 | windows, and (4) rearranges the protection registers to protect all of | |
97 | this. | |
98 | ||
99 | The reasons for doing this are: (1) the page at address 0 should be | |
100 | inaccessible so that NULL pointer errors can be caught; and (2) the bottom | |
101 | three quarters are left unoccupied so that an FR-V CPU with an MMU can use | |
102 | it for virtual userspace mappings. | |
103 | ||
104 | See include/asm-frv/mem-layout.h for constants pertaining to the memory | |
105 | layout. | |
106 | ||
107 | See include/asm-frv/mb-regs.h for the constants pertaining to the I/O bus | |
108 | controller configuration. | |
109 | ||
110 | ||
111 | (*) uClinux Memory Protection | |
112 | ||
113 | A DAMPR register is used to cover the entire region used for I/O | |
114 | (0xE0000000 - 0xFFFFFFFF). This permits the kernel to make uncached | |
115 | accesses to this region. Userspace is not permitted to access it. | |
116 | ||
117 | The DAMPR/IAMPR protection registers not in use for any other purpose are | |
118 | tiled over the top of the SDRAM such that: | |
119 | ||
120 | (1) The core kernel image is covered by as small a tile as possible | |
121 | granting only the kernel access to the underlying data, whilst | |
122 | making sure no SDRAM is actually made unavailable by this approach. | |
123 | ||
124 | (2) All other tiles are arranged to permit userspace access to the rest | |
125 | of the SDRAM. | |
126 | ||
127 | Barring point (1), there is nothing to protect kernel data against | |
128 | userspace damage - but this is uClinux. | |
129 | ||
130 | ||
131 | (*) Exceptions and Fixups | |
132 | ||
133 | Since the FR40x and FR55x CPUs that do not have full MMUs generate | |
134 | imprecise data error exceptions, there are currently no automatic fixup | |
135 | services available in uClinux. This includes misaligned memory access | |
136 | fixups. | |
137 | ||
138 | Userspace EFAULT errors can be trapped by issuing a MEMBAR instruction and | |
139 | forcing the fault to happen there. | |
140 | ||
141 | On the FR451, however, data exceptions are mostly precise, and so | |
142 | exception fixup handling is implemented as normal. | |
143 | ||
144 | ||
145 | (*) Userspace Breakpoints | |
146 | ||
147 | The ptrace() system call supports the following userspace debugging | |
148 | features: | |
149 | ||
150 | (1) Hardware assisted single step. | |
151 | ||
152 | (2) Breakpoint via the FR-V "BREAK" instruction. | |
153 | ||
154 | (3) Breakpoint via the FR-V "TIRA GR0, #1" instruction. | |
155 | ||
156 | (4) Syscall entry/exit trap. | |
157 | ||
158 | Each of the above generates a SIGTRAP. | |
159 | ||
160 | ||
161 | (*) On-Chip Serial Ports | |
162 | ||
163 | The FR-V on-chip serial ports are made available as ttyS0 and ttyS1. Note | |
164 | that if the GDB stub is compiled in, ttyS1 will not actually be available | |
165 | as it will be being used for the GDB stub. | |
166 | ||
167 | These ports can be made by: | |
168 | ||
169 | mknod /dev/ttyS0 c 4 64 | |
170 | mknod /dev/ttyS1 c 4 65 | |
171 | ||
172 | ||
173 | (*) Maskable Interrupts | |
174 | ||
175 | Level 15 (Non-maskable) interrupts are dealt with by the GDB stub if | |
176 | present, and cause a panic if not. If the GDB stub is present, ttyS1's | |
177 | interrupts are rated at level 15. | |
178 | ||
179 | All other interrupts are distributed over the set of available priorities | |
180 | so that no IRQs are shared where possible. The arch interrupt handling | |
181 | routines attempt to disentangle the various sources available through the | |
182 | CPU's own multiplexor, and those on off-CPU peripherals. | |
183 | ||
184 | ||
185 | (*) Accessing PCI Devices | |
186 | ||
187 | Where PCI is available, care must be taken when dealing with drivers that | |
188 | access PCI devices. PCI devices present their data in little-endian form, | |
189 | but the CPU sees it in big-endian form. The macros in asm/io.h try to get | |
190 | this right, but may not under all circumstances... | |
191 | ||
192 | ||
193 | (*) Ax88796 Ethernet Driver | |
194 | ||
195 | The MB93093 PDK board has an Ax88796 ethernet chipset (an NE2000 clone). A | |
196 | driver has been written to deal specifically with this. The driver | |
197 | provides MII services for the card. | |
198 | ||
199 | The driver can be configured by running make xconfig, and going to: | |
200 | ||
201 | (*) Network device support | |
202 | - turn on "Network device support" | |
203 | (*) Ethernet (10 or 100Mbit) | |
204 | - turn on "Ethernet (10 or 100Mbit)" | |
205 | - turn on "AX88796 NE2000 compatible chipset" | |
206 | ||
207 | The driver can be found in: | |
208 | ||
209 | drivers/net/ax88796.c | |
210 | include/asm/ax88796.h | |
211 | ||
212 | ||
213 | (*) WorkRAM Driver | |
214 | ||
215 | This driver provides a character device that permits access to the WorkRAM | |
216 | that can be found on the FR451 CPU. Each page is accessible through a | |
217 | separate minor number, thereby permitting each page to have its own | |
218 | filesystem permissions set on the device file. | |
219 | ||
220 | The device files should be: | |
221 | ||
222 | mknod /dev/frv/workram0 c 240 0 | |
223 | mknod /dev/frv/workram1 c 240 1 | |
224 | mknod /dev/frv/workram2 c 240 2 | |
225 | ... | |
226 | ||
227 | The driver will not permit the opening of any device file that does not | |
228 | correspond to at least a partial page of WorkRAM. So the first device file | |
229 | is the only one available on the FR451. If any other CPU is detected, none | |
230 | of the devices will be openable. | |
231 | ||
232 | The devices can be accessed with read, write and llseek, and can also be | |
233 | mmapped. If they're mmapped, they will only map at the appropriate | |
234 | 0x7e8nnnnn address on linux and at the 0xfe8nnnnn address on uClinux. If | |
235 | MAP_FIXED is not specified, the appropriate address will be chosen anyway. | |
236 | ||
237 | The mappings must be MAP_SHARED not MAP_PRIVATE, and must not be | |
238 | PROT_EXEC. They must also start at file offset 0, and must not be longer | |
239 | than one page in size. | |
240 | ||
241 | This driver can be configured by running make xconfig, and going to: | |
242 | ||
243 | (*) Character devices | |
244 | - turn on "Fujitsu FR-V CPU WorkRAM support" | |
245 | ||
246 | ||
247 | (*) Dynamic data cache write mode changing | |
248 | ||
249 | It is possible to view and to change the data cache's write mode through | |
250 | the /proc/sys/frv/cache-mode file while the kernel is running. There are | |
251 | two modes available: | |
252 | ||
253 | NAME MEANING | |
254 | ===== ========================================== | |
255 | wthru Data cache is in Write-Through mode | |
256 | wback Data cache is in Write-Back/Copy-Back mode | |
257 | ||
258 | To read the cache mode: | |
259 | ||
260 | # cat /proc/sys/frv/cache-mode | |
261 | wthru | |
262 | ||
263 | To change the cache mode: | |
264 | ||
265 | # echo wback >/proc/sys/frv/cache-mode | |
266 | # cat /proc/sys/frv/cache-mode | |
267 | wback | |
268 | ||
269 | ||
270 | (*) MMU Context IDs and Pinning | |
271 | ||
272 | On MMU Linux the CPU supports the concept of a context ID in its MMU to | |
273 | make it more efficient (TLB entries are labelled with a context ID to link | |
274 | them to specific tasks). | |
275 | ||
276 | Normally once a context ID is allocated, it will remain affixed to a task | |
277 | or CLONE_VM'd group of tasks for as long as it exists. However, since the | |
278 | kernel is capable of supporting more tasks than there are possible ID | |
279 | numbers, the kernel will pass context IDs from one task to another if | |
280 | there are insufficient available. | |
281 | ||
282 | The context ID currently in use by a task can be viewed in /proc: | |
283 | ||
284 | # grep CXNR /proc/1/status | |
285 | CXNR: 1 | |
286 | ||
287 | Note that kernel threads do not have a userspace context, and so will not | |
288 | show a CXNR entry in that file. | |
289 | ||
290 | Under some circumstances, however, it is desirable to pin a context ID on | |
291 | a process such that the kernel won't pass it on. This can be done by | |
292 | writing the process ID of the target process to a special file: | |
293 | ||
294 | # echo 17 >/proc/sys/frv/pin-cxnr | |
295 | ||
296 | Reading from the file will then show the context ID pinned. | |
297 | ||
298 | # cat /proc/sys/frv/pin-cxnr | |
299 | 4 | |
300 | ||
301 | The context ID will remain pinned as long as any process is using that | |
302 | context, i.e.: when the all the subscribing processes have exited or | |
303 | exec'd; or when an unpinning request happens: | |
304 | ||
305 | # echo 0 >/proc/sys/frv/pin-cxnr | |
306 | ||
307 | When there isn't a pinned context, the file shows -1: | |
308 | ||
309 | # cat /proc/sys/frv/pin-cxnr | |
310 | -1 |