I finally implemented a workaround to correct the problem:
in cpus.c : qemu_start_warp_timer(), in the "if (deadline > 0) { ... }"
part, I added:
CPUState *cpu;
CPU_FOREACH(cpu) {
atomic_mb_set(&cpu->exit_request, 1);
}
I do not understand more than 5% of the code I am messing up, so this
hack is probably broken...
Then I tested a bit more the code with different testcases... and I
found a new bug when writing a reload value smaller than the current
counter (the counter will then read as 0). It is due to this piece of
code in armv7m_systick.c : systick_read() :
/* The interrupt in triggered when the timer reaches zero.
However the counter is not reloaded until the next clock
tick. This is a hack to return zero during the first tick. */
if (val > s->reload) {
val = 0;
}
Well this is not really a prb for me with normal code, and it looks like
under control, but I can open another bug if needed.
--
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https://bugs.launchpad.net/bugs/1754038
Title:
ARM M: Systick first wrap delayed (qemu-timers/icount prb?)
Status in QEMU:
New
Bug description:
When running this kind of code with qemu:
static void SysTickISR(void)
{
printf("SysTick\n");
}
void main()
{
volatile int i, j;
printf("setup timer\n");
*(uint32_t*) 0xE000E014 = 0x8FFFFF; //reload value
*(uint32_t*) 0xE000E018 = 0; //force reload
*(uint32_t*) 0xE000E010 = 7; //cpu clk + ISR + enable
for (j = 0; j < 0x100; j++) {
for (i = 0; i < 0x100000; i++)
;
printf("cnt %08x -- %8x\n", *(uint32_t*) 0xE000E018,
*(uint32_t*)0xE000E010);
}
}
I get the following output (comments added after '#'):
setup timer
cnt 007cccca -- 7
cnt 006998a2 -- 7
cnt 00566479 -- 7
cnt 0043304f -- 7
cnt 002ffc26 -- 7
cnt 001cc7fd -- 7
cnt 000993d5 -- 7
cnt 00000000 -- 7 <--- problem here, systick should wrap and raise
isr
cnt 00000000 -- 7
cnt 00000000 -- 7
cnt 00000000 -- 7
cnt 00000000 -- 7
cnt 00000000 -- 7
cnt 00000000 -- 7
cnt 00000000 -- 7
cnt 00000000 -- 7
cnt 00000000 -- 7
cnt 00000000 -- 7
cnt 00000000 -- 7
cnt 00000000 -- 7
cnt 00000000 -- 7
SysTick <--- delayed isr occuring here
cnt 000986e0 -- 10007
SysTick
cnt 00865290 -- 10007 <---- then running fine as long as regs not
modified
cnt 00731e51 -- 7
cnt 005fea27 -- 7
cnt 004cb5ff -- 7
cnt 003981d6 -- 7
cnt 00264dad -- 7
cnt 00131984 -- 7
SysTick
cnt 008fe545 -- 10007
cnt 007cb106 -- 7
cnt 00697cdd -- 7
cnt 005648b4 -- 7
cnt 0043148b -- 7
cnt 002fe061 -- 7
cnt 001cac38 -- 7
cnt 00097810 -- 7
SysTick
cnt 008643d6 -- 10007
cnt 00730f97 -- 7
cnt 005fdb6d -- 7
cnt 004ca745 -- 7
cnt 0039731c -- 7
cnt 00263ef3 -- 7
cnt 00130aca -- 7
SysTick
cnt 008fd68b -- 10007
cnt 007ca24c -- 7
cnt 00696e23 -- 7
cnt 005639fa -- 7
cnt 004305d1 -- 7
cnt 002fd1a8 -- 7
cnt 001c9d7f -- 7
cnt 00096956 -- 7
SysTick
cnt 0086351d -- 10007
cnt 007300dd -- 7
cnt 005fccb4 -- 7
cnt 004c988c -- 7
cnt 00396463 -- 7
cnt 00263039 -- 7
cnt 0012fc10 -- 7
[...]
Command line and version:
qemu-system-arm -M lm3s6965evb -nographic -kernel hello.bin -monitor stdio
-serial file:/dev/pts/6 -icount 4 -cpu cortex-m4
QEMU 2.11.50
I am compiling from git repo, head is:
commit f32408f3b472a088467474ab152be3b6285b2d7b
Author: Daniel P. Berrangé <berra...@redhat.com>
Date: Tue Mar 6 13:43:17 2018 +0000
Config options:
./configure --target-list=arm-softmmu --enable-debug --disable-slirp
--enable-tcg-interpreter --disable-blobs --disable-docs --disable-guest-agent
--disable-gnutls --disable-nettle --disable-gcrypt --disable-sdl --disable-gtk
--disable-vnc --disable-virtfs --disable-mpath --disable-xen --disable-brlapi
--disable-curl --disable-bluez --disable-kvm --disable-hax --disable-hvf
--disable-whpx --disable-rdma --disable-vde --disable-netmap
--disable-linux-aio --disable-cap-ng --disable-attr --disable-vhost-net
--disable-spice --disable-rbd --disable-libiscsi --disable-libnfs
--disable-smartcard --disable-libusb --disable-live-block-migration
--disable-usb-redir --disable-lzo --disable-snappy --disable-bzip2
--disable-seccomp --disable-glusterfs --disable-tpm --disable-libssh2
--disable-numa --disable-libxml2 --disable-tcmalloc --disable-jemalloc
--disable-replication --disable-vhost-vsock --disable-opengl
--disable-virglrenderer --disable-xfsctl --disable-qom-cast-debug
--disable-vxhs --disable-crypto-afalg --disable-vhost-user --disable-capstone
--disable-pie --extra-cflags=-mtune=native
Not working with git tag 2.10.0 (almost same config)
Working with stock qemu-arm 2.5.0 from Ubuntu 16.04.
I started investigating, though I am not familiar with qemu code and I
could see that the execution is not geting out of
qemu_tcg_rr_cpu_thread_fn() 'while' loop and timers are not triggered
because the values in cpu->icount_extra or cpu->icount_budget are not
to modified accordingly after the timer is set (host side) when the
systick register is written (target side).
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