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raspi2: system timer device not implemented
In a small hobby kernel for Raspberry Pi 2B, I am using the system timer to control wait durations. This timer is located at 0x3f003000 and the timer counts are located at 0x3f003004 (CLO) and 0x3f004008 (CHI). Reading these memory locations returns 0 for both.
The basic code for this function is:
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@@ uint64_t ReadSysTimerCount() -- read the system time running count
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
ReadSysTimerCount:
ldr r0,=ST_CLO @ load the base address of the system timer
ldrd r0,r1,[r0] @ Get the 64-bit timer "count" into r1:r0
mov pc,lr @ return
Tracing back the definition of ST_CLO in my code:
#define ST_CLO (ST_BASE+4) // Counter Lower 32 bits
#define ST_BASE (HW_BASE+0x3000) // System Timer base address
#define HW_BASE (0x3f000000) // this is the base address for all hardware I/O addresses
I have tested a similar program that I know to work on real hardware with qemu-system-arm reading the same mmio register and have the same issue, so I'm pretty sure the issue is not with my code.
My Host PC is a VM on vmWare esxi running FC25 (8 cores, 8GB RAM):
[adam@os-dev ~]$ uname -a
Linux os-dev.jammin 4.10.8-200.fc25.x86_64 #1 SMP Fri Mar 31 13:20:22 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
I have confirmed this issue on QEMU 2.7.1 (fc25 Distro) and 2.9.0-rc3 (git).
adam@os-dev ~]$ qemu-system-arm --version
QEMU emulator version 2.7.1(qemu-2.7.1-4.fc25), Copyright (c) 2003-2016 Fabrice Bellard and the QEMU Project developers
[adam@os-dev ~]$ ./workspace/qemu/bin/debug/native/arm-softmmu/qemu-system-arm --version
QEMU emulator version 2.8.93 (v2.9.0-rc3-15-g5daf9b3)
Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers
A remote debugger for my kernel shows the following:
(gdb) info reg
r0 0x0 0
r1 0x0 0
r2 0x96 150
r3 0x0 0
r4 0xa000 40960
r5 0x0 0
r6 0x0 0
r7 0x0 0
r8 0x0 0
r9 0xa000 40960
r10 0x0 0
r11 0x7fdc 32732
r12 0x0 0
sp 0x7fc8 0x7fc8
lr 0x8194 33172
pc 0x80a4 0x80a4
cpsr 0x800001d3 -2147483181
(gdb) stepi
0x000080a8 in ?? ()
(gdb) info reg
r0 0x3f003004 1056976900
r1 0x0 0
r2 0x96 150
r3 0x0 0
r4 0xa000 40960
r5 0x0 0
r6 0x0 0
r7 0x0 0
r8 0x0 0
r9 0xa000 40960
r10 0x0 0
r11 0x7fdc 32732
r12 0x0 0
sp 0x7fc8 0x7fc8
lr 0x8194 33172
pc 0x80a8 0x80a8
cpsr 0x800001d3 -2147483181
(gdb) stepi
0x000080ac in ?? ()
(gdb) info reg
r0 0x0 0
r1 0x0 0
r2 0x96 150
r3 0x0 0
r4 0xa000 40960
r5 0x0 0
r6 0x0 0
r7 0x0 0
r8 0x0 0
r9 0xa000 40960
r10 0x0 0
r11 0x7fdc 32732
r12 0x0 0
sp 0x7fc8 0x7fc8
lr 0x8194 33172
pc 0x80ac 0x80ac
cpsr 0x800001d3 -2147483181
Notice r0 is loaded with the address for CLO and then cleared with 0 when read.
I am writing my code against the documented specifications in "BCM2835 ARM Peripherals" (attached for convenience), section "12 System Timer".
Please let me know if you need anything else from me.
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