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blinker01 example for pi2 in svc mode

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dwelch
2016-03-27 13:00:14 -04:00
parent bf2a3823e5
commit eb8aaccfaf
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71
boards/pi2/SVC/blinker01/Makefile Normal file
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ARMGNU ?= arm-none-eabi
AOPS = --warn --fatal-warnings
COPS = -Wall -Werror -O2 -nostdlib -nostartfiles -ffreestanding
gcc : blinker01.hex blinker01.bin
all : gcc clang
clean :
rm -f *.o
rm -f *.bin
rm -f *.hex
rm -f *.elf
rm -f *.list
rm -f *.img
rm -f *.bc
rm -f *.clang.opt.s
vectors.o : vectors.s
$(ARMGNU)-as vectors.s -o vectors.o
blinker01.o : blinker01.c
$(ARMGNU)-gcc $(COPS) -c blinker01.c -o blinker01.o
blinker01.elf : memmap vectors.o blinker01.o
$(ARMGNU)-ld vectors.o blinker01.o -T memmap -o blinker01.elf
$(ARMGNU)-objdump -D blinker01.elf > blinker01.list
blinker01.bin : blinker01.elf
$(ARMGNU)-objcopy blinker01.elf -O binary blinker01.bin
blinker01.hex : blinker01.elf
$(ARMGNU)-objcopy blinker01.elf -O ihex blinker01.hex
LOPS = -Wall -m32 -emit-llvm
LLCOPS = -march=arm -mcpu=arm1176jzf-s
LLCOPS0 = -march=arm
LLCOPS1 = -march=arm -mcpu=arm1176jzf-s
COPS = -Wall -O2 -nostdlib -nostartfiles -ffreestanding
#OOPS = -std-compile-opts
OOPS = -std-link-opts
clang : blinker01.clang.hex blinker01.clang.bin
blinker01.clang.bc : blinker01.c
clang $(LOPS) -c blinker01.c -o blinker01.clang.bc
blinker01.clang.opt.elf : memmap vectors.o blinker01.clang.bc
opt $(OOPS) blinker01.clang.bc -o blinker01.clang.opt.bc
llc $(LLCOPS) blinker01.clang.opt.bc -o blinker01.clang.opt.s
$(ARMGNU)-as blinker01.clang.opt.s -o blinker01.clang.opt.o
$(ARMGNU)-ld -o blinker01.clang.opt.elf -T memmap vectors.o blinker01.clang.opt.o
$(ARMGNU)-objdump -D blinker01.clang.opt.elf > blinker01.clang.opt.list
blinker01.clang.hex : blinker01.clang.opt.elf
$(ARMGNU)-objcopy blinker01.clang.opt.elf blinker01.clang.hex -O ihex
blinker01.clang.bin : blinker01.clang.opt.elf
$(ARMGNU)-objcopy blinker01.clang.opt.elf blinker01.clang.bin -O binary

129
boards/pi2/SVC/blinker01/README Normal file
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See the top level README for information on where to find documentation
for the raspberry pi and the ARM processor inside. Also find information
on how to load and run these programs.
This example is for the pi2, see other directories for other flavors
of raspberry pi. This example switches back to SVC mode from HYP mode.
This is an LED blinker example.
The pi2 has two LEDs tied to gpios 35 and 47.
Being the first example I will spend a little more time describing it.
I have some other ramblings on baremetal and the gnu tools so I will
try not to duplicate that.
The primary use case for the raspberry pi is to run some version of
linux. The three main files to do that are bootloader.bin, start.elf
and kernel.img. The first two being GPU programs the last being ARM.
If you have no other files (dont have a config.txt) they (starg.elf
GPU code) copy the kernel.img file to 0x8000 in RAM, place some
code at address 0x0000 that is intended to prepare the ARM for booting
linux, then branch to 0x8000. We simply replace the kernel.img file
with our own program. I prefer to not mess with config.txt stuff
because it is not the primary use case, most pis out there do not use
this, so without is significantly better tested. Also over time the
config.txt things you can play with come and go and change name, some
of the popular ones are undocumented and so on. So I really dont want
to rely on that. Simply replace the kernel.img and otherwise be stock.
vectors.s is the entry point for this program, even an application on
an operating system like linux has some assembly up front before
calling the main function. For this processor the minimum is to to
set up the stack pointer and call the main function. Because some
compilers add extra stuff if they see a main() funtion I use some
function name other than main() typically for embedded systems like this.
I have adopted the habit of using notmain() both to not be named main()
and to emphasize this is bare metal and not your average application.
See my ramblings on .data and .bss, I dont need/use them so the
bootstrap (little bit of assembly before calling the first C function)
does not have to prepare those segments. I only need to setup the
stack and call the first C function in the project.
I normally would set the stack pointer at the top of ram...Well that is
a lie, normaly one would do such a thing, but with code like this that
mostly ports across a number of boards, it becomes a pain keeping track
of who has how much ram. Instead for simple examples I set the stack
somewhere where it doesnt collide with the code, but also I dont have to
change every board. Because I am using the 0x8000 entry point I can
set the stack at 0x8000 and it will grow down toward 0x0000, and that
is more than enough for these projects. The way the ARM works it
subtracts then writes stuff so the first thing on the stack will really
be at 0x7FFC, you dont have to set it to 0x7FFC to avoid the code at
0x8000.
The gpio pin is setup as an output to drive the LED. The blink rate
appears to be around a couple-three times a second, but may vary based
on your compiler and settings. This program does not attempt to use
any other peripherals (a timer) it relies on simply wasting time in a
loop then changing the state of the LED. If you were to use this line
of code:
for(ra=0;ra<0x1000;ra++) continue;
The optimizer will replace that with this one assignment:
ra = 0x1000;
And actually since that value isnt used again, it is dead code the
optimizer will likely remove that as well.
One way to get around this is to make the loop variable volatile, this
tells the compiler every time you use it grab it from and save it back
to its home in ram. I prefer a different approach. I have a simple
dummy function in assembly language, it simply returns.
.globl dummy
dummy:
bx lr
The assembly is outside the visibility of the optimizer as would
anything basically not in the same file (llvm is a little different it
might "see" those other objects and optimize across them, gnu wont).
So by having that external function and by passing the loop variable
to it.
for(ra=0;ra<0x1000;ra++) dummy(ra);
We force the compiler to actually implement this code and run that loop
that many times. Dont need to declare the variable volatile. If
uncomfortable with assembly langauge you could create a dummy function
in a separately compiled file
void dummy ( void )
{
}
Which produces the same code.
00000000 <dummy>:
0: e12fff1e bx lr
Some toolchains have the ability to see across objects when they
optimize so you still have to be careful. I prefer the assembly approach
to defeating the optimizer.
So this program sets up the gpio to drive the LED. Uses the loop to kill
some time, changes state of the LED, repeat forever. The blink rate
will be the same for the same program. But compiler differences and
options can cause one build to be different from another in the blink
rate. It is not really deterministic, thus the desire to use timers in
the examples that follow. If you change the number the loop counts to
and re-build with the same tools, you should see a change in the
blink rate.
Note the Broadcom documentation uses addresses 0x7Exxxxxx for the
peripherals. That is we assume the GPU's address space to access those
things. The ARM window into that is to date either at 0x20xxxxxx or
0x3Fxxxxxx depending on the specific broadcom chip for that board type
the pi2 uses 0x3Fxxxxxx so when you see 0x7Exxxxxx replace that
0x7E with 0x3F.
I normally dont leave the compiled output in the repository, but you
may need it to compare with your results to see why for example mine
works and yours doesnt, so I will leave these here for this example.

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//-------------------------------------------------------------------------
//-------------------------------------------------------------------------
extern void PUT32 ( unsigned int, unsigned int );
extern unsigned int GET32 ( unsigned int );
extern void dummy ( unsigned int );
extern unsigned int GETCPSR ( void );
#define GPFSEL3 0x3F20000C
#define GPFSEL4 0x3F200010
#define GPSET1 0x3F200020
#define GPCLR1 0x3F20002C
//-------------------------------------------------------------------------
int notmain ( void )
{
unsigned int ra;
unsigned int rb;
ra=GET32(GPFSEL4);
ra&=~(7<<21);
ra|=1<<21;
PUT32(GPFSEL4,ra);
ra=GET32(GPFSEL3);
ra&=~(7<<15);
ra|=1<<15;
PUT32(GPFSEL3,ra);
ra=GETCPSR();
if((ra&0x1F)==0x1A) rb=0x20000;
else rb=0x10000;
while(1)
{
PUT32(GPSET1,1<<(47-32));
PUT32(GPCLR1,1<<(35-32));
for(ra=0;ra<rb;ra++) dummy(ra);
PUT32(GPCLR1,1<<(47-32));
PUT32(GPSET1,1<<(35-32));
for(ra=0;ra<rb;ra++) dummy(ra);
}
return(0);
}
//-------------------------------------------------------------------------
//-------------------------------------------------------------------------
//-------------------------------------------------------------------------
//
// Copyright (c) 2015 David Welch dwelch@dwelch.com
//
// Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
//-------------------------------------------------------------------------

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boards/pi2/SVC/blinker01/blinker01.elf Executable file
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boards/pi2/SVC/blinker01/blinker01.hex Normal file
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:1080000000000FE11F1000E21A0051E30500001A02
:108010001F00C0E3130080E300F06FE104008FE273
:1080200000F32EE16E0060E102D9A0E30F00A0E1B1
:10803000070000EBFEFFFFEA001080E51EFF2FE1C6
:10804000000090E51EFF2FE11EFF2FE100000FE171
:108050001EFF2FE170402DE9A0009FE5F7FFFFEB29
:108060000E16C0E3021681E390009FE5F1FFFFEBDF
:108070008C009FE5F1FFFFEB0E19C0E3021981E3CD
:108080007C009FE5EBFFFFEBEFFFFFEB1F0000E243
:108090001A0050E30258A0030158A0130219A0E3EC
:1080A00060009FE5E3FFFFEB0810A0E358009FE5A9
:1080B000E0FFFFEB0040A0E30400A0E1014084E208
:1080C000E0FFFFEB040055E1FAFFFF1A0219A0E3FD
:1080D00034009FE5D7FFFFEB0810A0E324009FE5E5
:1080E000D4FFFFEB0040A0E30400A0E1014084E2E4
:1080F000D4FFFFEB040055E1FAFFFF1AE6FFFFEAA9
:108100001000203F0C00203F2000203F2C00203F8B
:040000030000800079
:00000001FF

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boards/pi2/SVC/blinker01/blinker01.list Normal file
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blinker01.elf: file format elf32-littlearm
Disassembly of section .text:
00008000 <_start>:
8000: e10f0000 mrs r0, CPSR
8004: e200101f and r1, r0, #31
8008: e351001a cmp r1, #26
800c: 1a000005 bne 8028 <skip>
8010: e3c0001f bic r0, r0, #31
8014: e3800013 orr r0, r0, #19
8018: e16ff000 msr SPSR_fsxc, r0
801c: e28f0004 add r0, pc, #4
8020: e12ef300 msr ELR_hyp, r0
8024: e160006e eret
00008028 <skip>:
8028: e3a0d902 mov sp, #32768 ; 0x8000
802c: e1a0000f mov r0, pc
8030: eb000007 bl 8054 <notmain>
00008034 <hang>:
8034: eafffffe b 8034 <hang>
00008038 <PUT32>:
8038: e5801000 str r1, [r0]
803c: e12fff1e bx lr
00008040 <GET32>:
8040: e5900000 ldr r0, [r0]
8044: e12fff1e bx lr
00008048 <dummy>:
8048: e12fff1e bx lr
0000804c <GETCPSR>:
804c: e10f0000 mrs r0, CPSR
8050: e12fff1e bx lr
00008054 <notmain>:
8054: e92d4070 push {r4, r5, r6, lr}
8058: e59f00a0 ldr r0, [pc, #160] ; 8100 <notmain+0xac>
805c: ebfffff7 bl 8040 <GET32>
8060: e3c0160e bic r1, r0, #14680064 ; 0xe00000
8064: e3811602 orr r1, r1, #2097152 ; 0x200000
8068: e59f0090 ldr r0, [pc, #144] ; 8100 <notmain+0xac>
806c: ebfffff1 bl 8038 <PUT32>
8070: e59f008c ldr r0, [pc, #140] ; 8104 <notmain+0xb0>
8074: ebfffff1 bl 8040 <GET32>
8078: e3c0190e bic r1, r0, #229376 ; 0x38000
807c: e3811902 orr r1, r1, #32768 ; 0x8000
8080: e59f007c ldr r0, [pc, #124] ; 8104 <notmain+0xb0>
8084: ebffffeb bl 8038 <PUT32>
8088: ebffffef bl 804c <GETCPSR>
808c: e200001f and r0, r0, #31
8090: e350001a cmp r0, #26
8094: 03a05802 moveq r5, #131072 ; 0x20000
8098: 13a05801 movne r5, #65536 ; 0x10000
809c: e3a01902 mov r1, #32768 ; 0x8000
80a0: e59f0060 ldr r0, [pc, #96] ; 8108 <notmain+0xb4>
80a4: ebffffe3 bl 8038 <PUT32>
80a8: e3a01008 mov r1, #8
80ac: e59f0058 ldr r0, [pc, #88] ; 810c <notmain+0xb8>
80b0: ebffffe0 bl 8038 <PUT32>
80b4: e3a04000 mov r4, #0
80b8: e1a00004 mov r0, r4
80bc: e2844001 add r4, r4, #1
80c0: ebffffe0 bl 8048 <dummy>
80c4: e1550004 cmp r5, r4
80c8: 1afffffa bne 80b8 <notmain+0x64>
80cc: e3a01902 mov r1, #32768 ; 0x8000
80d0: e59f0034 ldr r0, [pc, #52] ; 810c <notmain+0xb8>
80d4: ebffffd7 bl 8038 <PUT32>
80d8: e3a01008 mov r1, #8
80dc: e59f0024 ldr r0, [pc, #36] ; 8108 <notmain+0xb4>
80e0: ebffffd4 bl 8038 <PUT32>
80e4: e3a04000 mov r4, #0
80e8: e1a00004 mov r0, r4
80ec: e2844001 add r4, r4, #1
80f0: ebffffd4 bl 8048 <dummy>
80f4: e1550004 cmp r5, r4
80f8: 1afffffa bne 80e8 <notmain+0x94>
80fc: eaffffe6 b 809c <notmain+0x48>
8100: 3f200010 svccc 0x00200010
8104: 3f20000c svccc 0x0020000c
8108: 3f200020 svccc 0x00200020
810c: 3f20002c svccc 0x0020002c
Disassembly of section .ARM.attributes:
00000000 <.ARM.attributes>:
0: 00002b41 andeq r2, r0, r1, asr #22
4: 61656100 cmnvs r5, r0, lsl #2
8: 01006962 tsteq r0, r2, ror #18
c: 00000021 andeq r0, r0, r1, lsr #32
10: 4d524105 ldfmie f4, [r2, #-20] ; 0xffffffec
14: 00377620 eorseq r7, r7, r0, lsr #12
18: 01080a06 tsteq r8, r6, lsl #20
1c: 04120109 ldreq r0, [r2], #-265 ; 0xfffffef7
20: 01150114 tsteq r5, r4, lsl r1
24: 01180317 tsteq r8, r7, lsl r3
28: 0244011a subeq r0, r4, #-2147483642 ; 0x80000006
Disassembly of section .comment:
00000000 <.comment>:
0: 3a434347 bcc 10d0d24 <notmain+0x10c8cd0>
4: 4e472820 cdpmi 8, 4, cr2, cr7, cr0, {1}
8: 35202955 strcc r2, [r0, #-2389]! ; 0xfffff6ab
c: 302e332e eorcc r3, lr, lr, lsr #6
...

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MEMORY
{
ram : ORIGIN = 0x8000, LENGTH = 0x10000
}
SECTIONS
{
.text : { *(.text*) } > ram
.bss : { *(.bss*) } > ram
}

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;@ ------------------------------------------------------------------
;@ ------------------------------------------------------------------
.globl _start
_start:
;@ b skip
mrs r0,cpsr
and r1,r0,#0x1F
cmp r1,#0x1A
bne skip
bic r0,r0,#0x1F
orr r0,r0,#0x13
msr spsr_cxsf,r0
add r0,pc,#4
msr ELR_hyp,r0 ;@ .word 0xe12ef300
eret ;@ .word 0xe160006e
skip:
mov sp,#0x8000
mov r0,pc
bl notmain
hang: b hang
.globl PUT32
PUT32:
str r1,[r0]
bx lr
.globl GET32
GET32:
ldr r0,[r0]
bx lr
.globl dummy
dummy:
bx lr
.globl GETCPSR
GETCPSR:
mrs r0,cpsr
bx lr
;@-------------------------------------------------------------------------
;@-------------------------------------------------------------------------
;@-------------------------------------------------------------------------
;@
;@ Copyright (c) 2012 David Welch dwelch@dwelch.com
;@
;@ Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
;@
;@ The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
;@
;@ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
;@
;@-------------------------------------------------------------------------