Le 10/03/2021 à 09:09, Mark Cave-Ayland a écrit :
> The original implementation of the Macintosh VIA devices in commit 6dca62a000
> "hw/m68k: add VIA support" used timer optimisations to reduce high CPU usage
> on
> the host when booting Linux. These optimisations worked by waiting until VIA1
> port B was accessed before re-arming the timers.
>
> The MacOS toolbox ROM constantly writes to VIA1 port B which calls
> via1_one_second_update() and via1_sixty_hz_update() to calculate the new
> expiry
> time, causing the timers to constantly reset and never fire. The effect of
> this
> is that the Ticks (0x16a) global variable holding the number of 60Hz timer
> ticks
> since reset is never incremented by the interrupt causing time to stand still.
>
> Whilst the code was introduced as a performance optimisation, it is likely
> that
> the high CPU usage was actually caused by the incorrect 60Hz timer interval
> fixed in the previous patch. Remove the optimisation to keep everything simple
> and enable the MacOS toolbox ROM to start keeping time.
>
> Signed-off-by: Mark Cave-Ayland <mark.cave-ayl...@ilande.co.uk>
> ---
> hw/misc/mac_via.c | 43 ++++---------------------------------------
> 1 file changed, 4 insertions(+), 39 deletions(-)
>
> diff --git a/hw/misc/mac_via.c b/hw/misc/mac_via.c
> index c6e1552a59..23b11dd522 100644
> --- a/hw/misc/mac_via.c
> +++ b/hw/misc/mac_via.c
> @@ -299,30 +299,17 @@ enum {
>
> static void via1_sixty_hz_update(MOS6522Q800VIA1State *v1s)
> {
> - MOS6522State *s = MOS6522(v1s);
> -
> /* 60 Hz irq */
> v1s->next_sixty_hz = (qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + 16630000) /
> 16630000 * 16630000;
> -
> - if (s->ier & VIA1_IRQ_60HZ) {
> - timer_mod(v1s->sixty_hz_timer, v1s->next_sixty_hz);
> - } else {
> - timer_del(v1s->sixty_hz_timer);
> - }
> + timer_mod(v1s->sixty_hz_timer, v1s->next_sixty_hz);
> }
>
> static void via1_one_second_update(MOS6522Q800VIA1State *v1s)
> {
> - MOS6522State *s = MOS6522(v1s);
> -
> v1s->next_second = (qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) + 1000) /
> 1000 * 1000;
> - if (s->ier & VIA1_IRQ_ONE_SECOND) {
> - timer_mod(v1s->one_second_timer, v1s->next_second);
> - } else {
> - timer_del(v1s->one_second_timer);
> - }
> + timer_mod(v1s->one_second_timer, v1s->next_second);
> }
>
> static void via1_sixty_hz(void *opaque)
> @@ -893,21 +880,6 @@ static uint64_t mos6522_q800_via1_read(void *opaque,
> hwaddr addr, unsigned size)
> {
> MOS6522Q800VIA1State *s = MOS6522_Q800_VIA1(opaque);
> MOS6522State *ms = MOS6522(s);
> - int64_t now = qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL);
> -
> - /*
> - * If IRQs are disabled, timers are disabled, but we need to update
> - * VIA1_IRQ_60HZ and VIA1_IRQ_ONE_SECOND bits in the IFR
> - */
> -
> - if (now >= s->next_sixty_hz) {
> - ms->ifr |= VIA1_IRQ_60HZ;
> - via1_sixty_hz_update(s);
> - }
> - if (now >= s->next_second) {
> - ms->ifr |= VIA1_IRQ_ONE_SECOND;
> - via1_one_second_update(s);
> - }
>
> addr = (addr >> 9) & 0xf;
> return mos6522_read(ms, addr, size);
> @@ -931,9 +903,6 @@ static void mos6522_q800_via1_write(void *opaque, hwaddr
> addr, uint64_t val,
> v1s->last_b = ms->b;
> break;
> }
> -
> - via1_one_second_update(v1s);
> - via1_sixty_hz_update(v1s);
> }
>
> static const MemoryRegionOps mos6522_q800_via1_ops = {
> @@ -978,16 +947,10 @@ static const MemoryRegionOps mos6522_q800_via2_ops = {
> static void mac_via_reset(DeviceState *dev)
> {
> MacVIAState *m = MAC_VIA(dev);
> - MOS6522Q800VIA1State *v1s = &m->mos6522_via1;
> ADBBusState *adb_bus = &m->adb_bus;
>
> adb_set_autopoll_enabled(adb_bus, true);
>
> - timer_del(v1s->sixty_hz_timer);
> - v1s->next_sixty_hz = 0;
> - timer_del(v1s->one_second_timer);
> - v1s->next_second = 0;
> -
> m->cmd = REG_EMPTY;
> m->alt = REG_EMPTY;
> }
> @@ -1026,9 +989,11 @@ static void mac_via_realize(DeviceState *dev, Error
> **errp)
> m->mos6522_via1.one_second_timer = timer_new_ms(QEMU_CLOCK_VIRTUAL,
> via1_one_second,
> &m->mos6522_via1);
> + via1_one_second_update(&m->mos6522_via1);
> m->mos6522_via1.sixty_hz_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
> via1_sixty_hz,
> &m->mos6522_via1);
> + via1_sixty_hz_update(&m->mos6522_via1);
>
> qemu_get_timedate(&tm, 0);
> m->tick_offset = (uint32_t)mktimegm(&tm) + RTC_OFFSET;
>
Reviewed-by: Laurent Vivier <laur...@vivier.eu>
