diff mbox series

[rc1,12/24] hw/timer: Add limited support for Atmel 16 bit timer peripheral

Message ID 20200123000307.11541-13-richard.henderson@linaro.org
State New
Headers show
Series target/avr merger | expand

Commit Message

Richard Henderson Jan. 23, 2020, 12:02 a.m. UTC
From: Michael Rolnik <mrolnik@gmail.com>

These were designed to facilitate testing but should provide enough
function to be useful in other contexts.  Only a subset of the functions
of each peripheral is implemented, mainly due to the lack of a standard
way to handle electrical connections (like GPIO pins).

Signed-off-by: Sarah Harris <S.E.Harris@kent.ac.uk>
Message-Id: <20200118191416.19934-13-mrolnik@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
[rth: Squash info mtree fixes and a file rename from f4bug, which was:]
Suggested-by: Aleksandar Markovic <aleksandar.m.mail@gmail.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 include/hw/timer/atmel_timer16.h |  94 +++++
 hw/timer/atmel_timer16.c         | 602 +++++++++++++++++++++++++++++++
 hw/timer/Kconfig                 |   3 +
 hw/timer/Makefile.objs           |   2 +
 4 files changed, 701 insertions(+)
 create mode 100644 include/hw/timer/atmel_timer16.h
 create mode 100644 hw/timer/atmel_timer16.c

Comments

Thomas Huth Jan. 23, 2020, 4:49 a.m. UTC | #1
On 23/01/2020 01.02, Richard Henderson wrote:
> From: Michael Rolnik <mrolnik@gmail.com>
> 
> These were designed to facilitate testing but should provide enough
> function to be useful in other contexts.  Only a subset of the functions
> of each peripheral is implemented, mainly due to the lack of a standard
> way to handle electrical connections (like GPIO pins).
> 
> Signed-off-by: Sarah Harris <S.E.Harris@kent.ac.uk>
> Message-Id: <20200118191416.19934-13-mrolnik@gmail.com>
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> [rth: Squash info mtree fixes and a file rename from f4bug, which was:]
> Suggested-by: Aleksandar Markovic <aleksandar.m.mail@gmail.com>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
[...]
> +static void avr_timer16_clksrc_update(AVRTimer16State *t16)
> +{
> +    uint16_t divider = 0;
> +    switch (CLKSRC(t16)) {
> +    case T16_CLKSRC_EXT_FALLING:
> +    case T16_CLKSRC_EXT_RISING:
> +        ERROR("external clock source unsupported");

Maybe this should rather be qemu_log_mask(LOG_UNIMP, ...) instead?

> +        goto end;
> +    case T16_CLKSRC_STOPPED:
> +        goto end;
> +    case T16_CLKSRC_DIV1:
> +        divider = 1;
> +        break;
> +    case T16_CLKSRC_DIV8:
> +        divider = 8;
> +        break;
> +    case T16_CLKSRC_DIV64:
> +        divider = 64;
> +        break;
> +    case T16_CLKSRC_DIV256:
> +        divider = 256;
> +        break;
> +    case T16_CLKSRC_DIV1024:
> +        divider = 1024;
> +        break;
> +    default:
> +        goto end;
> +    }
> +    t16->freq_hz = t16->cpu_freq_hz / divider;
> +    t16->period_ns = NANOSECONDS_PER_SECOND / t16->freq_hz;
> +    DB_PRINT("Timer frequency %" PRIu64 " hz, period %" PRIu64 " ns (%f s)",
> +             t16->freq_hz, t16->period_ns, 1 / (double)t16->freq_hz);
> +end:
> +    return;
> +}

Nit: You could use an early "return" instead of "goto end" and the
superfluous return statement at the end of the function.

> +static void avr_timer16_set_alarm(AVRTimer16State *t16)
> +{
> +    if (CLKSRC(t16) == T16_CLKSRC_EXT_FALLING ||
> +        CLKSRC(t16) == T16_CLKSRC_EXT_RISING ||
> +        CLKSRC(t16) == T16_CLKSRC_STOPPED) {
> +        /* Timer is disabled or set to external clock source (unsupported) */
> +        goto end;
> +    }
> +
> +    uint64_t alarm_offset = 0xffff;
> +    enum NextInterrupt next_interrupt = OVERFLOW;
> +
> +    switch (MODE(t16)) {
> +    case T16_MODE_NORMAL:
> +        /* Normal mode */
> +        if (OCRA(t16) < alarm_offset && OCRA(t16) > CNT(t16) &&
> +            (t16->imsk & T16_INT_OCA)) {
> +            alarm_offset = OCRA(t16);
> +            next_interrupt = COMPA;
> +        }
> +        break;
> +    case T16_MODE_CTC_OCRA:
> +        /* CTC mode, top = ocra */
> +        if (OCRA(t16) < alarm_offset && OCRA(t16) > CNT(t16)) {
> +            alarm_offset = OCRA(t16);
> +            next_interrupt = COMPA;
> +        }
> +       break;
> +    case T16_MODE_CTC_ICR:
> +        /* CTC mode, top = icr */
> +        if (ICR(t16) < alarm_offset && ICR(t16) > CNT(t16)) {
> +            alarm_offset = ICR(t16);
> +            next_interrupt = CAPT;
> +        }
> +        if (OCRA(t16) < alarm_offset && OCRA(t16) > CNT(t16) &&
> +            (t16->imsk & T16_INT_OCA)) {
> +            alarm_offset = OCRA(t16);
> +            next_interrupt = COMPA;
> +        }
> +        break;
> +    default:
> +        ERROR("pwm modes are unsupported");

qemu_log_mask(LOG_UNIMP, ...) ?

> +        goto end;
> +    }
> +    if (OCRB(t16) < alarm_offset && OCRB(t16) > CNT(t16) &&
> +        (t16->imsk & T16_INT_OCB)) {
> +        alarm_offset = OCRB(t16);
> +        next_interrupt = COMPB;
> +    }
> +    if (OCRC(t16) < alarm_offset && OCRB(t16) > CNT(t16) &&
> +        (t16->imsk & T16_INT_OCC)) {
> +        alarm_offset = OCRB(t16);
> +        next_interrupt = COMPC;
> +    }
> +    alarm_offset -= CNT(t16);
> +
> +    t16->next_interrupt = next_interrupt;
> +    uint64_t alarm_ns =
> +        t16->reset_time_ns + ((CNT(t16) + alarm_offset) * t16->period_ns);
> +    timer_mod(t16->timer, alarm_ns);
> +
> +    DB_PRINT("next alarm %" PRIu64 " ns from now",
> +        alarm_offset * t16->period_ns);
> +
> +end:
> +    return;
> +}

This function could also use early returns instead of "goto end".

(no need to respin just because of these nits ... but maybe something to
consider if you respin anyway)

 Thomas
Philippe Mathieu-Daudé Jan. 23, 2020, 5:29 p.m. UTC | #2
On 1/23/20 5:49 AM, Thomas Huth wrote:
> On 23/01/2020 01.02, Richard Henderson wrote:
>> From: Michael Rolnik <mrolnik@gmail.com>
>>
>> These were designed to facilitate testing but should provide enough
>> function to be useful in other contexts.  Only a subset of the functions
>> of each peripheral is implemented, mainly due to the lack of a standard
>> way to handle electrical connections (like GPIO pins).
>>
>> Signed-off-by: Sarah Harris <S.E.Harris@kent.ac.uk>
>> Message-Id: <20200118191416.19934-13-mrolnik@gmail.com>
>> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>> [rth: Squash info mtree fixes and a file rename from f4bug, which was:]
>> Suggested-by: Aleksandar Markovic <aleksandar.m.mail@gmail.com>
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> ---
> [...]
>> +static void avr_timer16_clksrc_update(AVRTimer16State *t16)
>> +{
>> +    uint16_t divider = 0;
>> +    switch (CLKSRC(t16)) {
>> +    case T16_CLKSRC_EXT_FALLING:
>> +    case T16_CLKSRC_EXT_RISING:
>> +        ERROR("external clock source unsupported");
> 
> Maybe this should rather be qemu_log_mask(LOG_UNIMP, ...) instead?

Yes.

>> +        goto end;
>> +    case T16_CLKSRC_STOPPED:
>> +        goto end;
>> +    case T16_CLKSRC_DIV1:
>> +        divider = 1;
>> +        break;
>> +    case T16_CLKSRC_DIV8:
>> +        divider = 8;
>> +        break;
>> +    case T16_CLKSRC_DIV64:
>> +        divider = 64;
>> +        break;
>> +    case T16_CLKSRC_DIV256:
>> +        divider = 256;
>> +        break;
>> +    case T16_CLKSRC_DIV1024:
>> +        divider = 1024;
>> +        break;
>> +    default:
>> +        goto end;
>> +    }
>> +    t16->freq_hz = t16->cpu_freq_hz / divider;
>> +    t16->period_ns = NANOSECONDS_PER_SECOND / t16->freq_hz;
>> +    DB_PRINT("Timer frequency %" PRIu64 " hz, period %" PRIu64 " ns (%f s)",
>> +             t16->freq_hz, t16->period_ns, 1 / (double)t16->freq_hz);
>> +end:
>> +    return;
>> +}
> 
> Nit: You could use an early "return" instead of "goto end" and the
> superfluous return statement at the end of the function.

I'd prefer use a 'break' statement, and check if divider != then { set 
values and log trace event}.

>> +static void avr_timer16_set_alarm(AVRTimer16State *t16)
>> +{
>> +    if (CLKSRC(t16) == T16_CLKSRC_EXT_FALLING ||
>> +        CLKSRC(t16) == T16_CLKSRC_EXT_RISING ||
>> +        CLKSRC(t16) == T16_CLKSRC_STOPPED) {
>> +        /* Timer is disabled or set to external clock source (unsupported) */
>> +        goto end;
>> +    }
>> +
>> +    uint64_t alarm_offset = 0xffff;
>> +    enum NextInterrupt next_interrupt = OVERFLOW;
>> +
>> +    switch (MODE(t16)) {
>> +    case T16_MODE_NORMAL:
>> +        /* Normal mode */
>> +        if (OCRA(t16) < alarm_offset && OCRA(t16) > CNT(t16) &&
>> +            (t16->imsk & T16_INT_OCA)) {
>> +            alarm_offset = OCRA(t16);
>> +            next_interrupt = COMPA;
>> +        }
>> +        break;
>> +    case T16_MODE_CTC_OCRA:
>> +        /* CTC mode, top = ocra */
>> +        if (OCRA(t16) < alarm_offset && OCRA(t16) > CNT(t16)) {
>> +            alarm_offset = OCRA(t16);
>> +            next_interrupt = COMPA;
>> +        }
>> +       break;
>> +    case T16_MODE_CTC_ICR:
>> +        /* CTC mode, top = icr */
>> +        if (ICR(t16) < alarm_offset && ICR(t16) > CNT(t16)) {
>> +            alarm_offset = ICR(t16);
>> +            next_interrupt = CAPT;
>> +        }
>> +        if (OCRA(t16) < alarm_offset && OCRA(t16) > CNT(t16) &&
>> +            (t16->imsk & T16_INT_OCA)) {
>> +            alarm_offset = OCRA(t16);
>> +            next_interrupt = COMPA;
>> +        }
>> +        break;
>> +    default:
>> +        ERROR("pwm modes are unsupported");
> 
> qemu_log_mask(LOG_UNIMP, ...) ?
> 
>> +        goto end;
>> +    }
>> +    if (OCRB(t16) < alarm_offset && OCRB(t16) > CNT(t16) &&
>> +        (t16->imsk & T16_INT_OCB)) {
>> +        alarm_offset = OCRB(t16);
>> +        next_interrupt = COMPB;
>> +    }
>> +    if (OCRC(t16) < alarm_offset && OCRB(t16) > CNT(t16) &&
>> +        (t16->imsk & T16_INT_OCC)) {
>> +        alarm_offset = OCRB(t16);
>> +        next_interrupt = COMPC;
>> +    }
>> +    alarm_offset -= CNT(t16);
>> +
>> +    t16->next_interrupt = next_interrupt;
>> +    uint64_t alarm_ns =
>> +        t16->reset_time_ns + ((CNT(t16) + alarm_offset) * t16->period_ns);
>> +    timer_mod(t16->timer, alarm_ns);
>> +
>> +    DB_PRINT("next alarm %" PRIu64 " ns from now",
>> +        alarm_offset * t16->period_ns);
>> +
>> +end:
>> +    return;
>> +}
> 
> This function could also use early returns instead of "goto end".
> 
> (no need to respin just because of these nits ... but maybe something to
> consider if you respin anyway)
> 
>   Thomas
> 
>
diff mbox series

Patch

diff --git a/include/hw/timer/atmel_timer16.h b/include/hw/timer/atmel_timer16.h
new file mode 100644
index 0000000000..f0516c41cf
--- /dev/null
+++ b/include/hw/timer/atmel_timer16.h
@@ -0,0 +1,94 @@ 
+/*
+ * Atmel AVR 16 bit timer
+ *
+ * Copyright (c) 2018 University of Kent
+ * Author: Ed Robbins
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see
+ * <http://www.gnu.org/licenses/lgpl-2.1.html>
+ */
+
+/*
+ * Driver for 16 bit timers on 8 bit AVR devices.
+ * Note:
+ * On ATmega640/V-1280/V-1281/V-2560/V-2561/V timers 1, 3, 4 and 5 are 16 bit
+ */
+
+#ifndef HW_TIMER_ATMEL_TIMER16_H
+#define HW_TIMER_ATMEL_TIMER16_H
+
+#include "hw/sysbus.h"
+#include "qemu/timer.h"
+#include "hw/hw.h"
+
+enum NextInterrupt {
+    OVERFLOW,
+    COMPA,
+    COMPB,
+    COMPC,
+    CAPT
+};
+
+#define TYPE_AVR_TIMER16 "atmel-timer16"
+#define AVR_TIMER16(obj) \
+    OBJECT_CHECK(AVRTimer16State, (obj), TYPE_AVR_TIMER16)
+
+typedef struct AVRTimer16State {
+    /* <private> */
+    SysBusDevice parent_obj;
+
+    /* <public> */
+    MemoryRegion iomem;
+    MemoryRegion imsk_iomem;
+    MemoryRegion ifr_iomem;
+    QEMUTimer *timer;
+    qemu_irq capt_irq;
+    qemu_irq compa_irq;
+    qemu_irq compb_irq;
+    qemu_irq compc_irq;
+    qemu_irq ovf_irq;
+
+    bool enabled;
+
+    /* registers */
+    uint8_t cra;
+    uint8_t crb;
+    uint8_t crc;
+    uint8_t cntl;
+    uint8_t cnth;
+    uint8_t icrl;
+    uint8_t icrh;
+    uint8_t ocral;
+    uint8_t ocrah;
+    uint8_t ocrbl;
+    uint8_t ocrbh;
+    uint8_t ocrcl;
+    uint8_t ocrch;
+    /*
+     * Reads and writes to CNT and ICR utilise a bizarre temporary
+     * register, which we emulate
+     */
+    uint8_t rtmp;
+    uint8_t imsk;
+    uint8_t ifr;
+
+    uint8_t id;
+    uint64_t cpu_freq_hz;
+    uint64_t freq_hz;
+    uint64_t period_ns;
+    uint64_t reset_time_ns;
+    enum NextInterrupt next_interrupt;
+} AVRTimer16State;
+
+#endif /* HW_TIMER_ATMEL_TIMER16_H */
diff --git a/hw/timer/atmel_timer16.c b/hw/timer/atmel_timer16.c
new file mode 100644
index 0000000000..3b06d6e4e5
--- /dev/null
+++ b/hw/timer/atmel_timer16.c
@@ -0,0 +1,602 @@ 
+/*
+ * Atmel AVR 16 bit timer
+ *
+ * Copyright (c) 2018 University of Kent
+ * Author: Ed Robbins
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see
+ * <http://www.gnu.org/licenses/lgpl-2.1.html>
+ */
+
+/*
+ * Driver for 16 bit timers on 8 bit AVR devices.
+ * Note:
+ * ATmega640/V-1280/V-1281/V-2560/V-2561/V timers 1, 3, 4 and 5 are 16 bit
+ */
+
+/*
+ * XXX TODO: Power Reduction Register support
+ *           prescaler pause support
+ *           PWM modes, GPIO, output capture pins, input compare pin
+ */
+
+#include "qemu/osdep.h"
+#include "hw/timer/atmel_timer16.h"
+#include "qemu/log.h"
+#include "hw/irq.h"
+#include "hw/qdev-properties.h"
+
+/* Register offsets */
+#define T16_CRA     0x0
+#define T16_CRB     0x1
+#define T16_CRC     0x2
+#define T16_CNTL    0x4
+#define T16_CNTH    0x5
+#define T16_ICRL    0x6
+#define T16_ICRH    0x7
+#define T16_OCRAL   0x8
+#define T16_OCRAH   0x9
+#define T16_OCRBL   0xa
+#define T16_OCRBH   0xb
+#define T16_OCRCL   0xc
+#define T16_OCRCH   0xd
+
+/* Field masks */
+#define T16_CRA_WGM01   0x3
+#define T16_CRA_COMC    0xc
+#define T16_CRA_COMB    0x30
+#define T16_CRA_COMA    0xc0
+#define T16_CRA_OC_CONF \
+    (T16_CRA_COMA | T16_CRA_COMB | T16_CRA_COMC)
+
+#define T16_CRB_CS      0x7
+#define T16_CRB_WGM23   0x18
+#define T16_CRB_ICES    0x40
+#define T16_CRB_ICNC    0x80
+
+#define T16_CRC_FOCC    0x20
+#define T16_CRC_FOCB    0x40
+#define T16_CRC_FOCA    0x80
+
+/* Fields masks both TIMSK and TIFR (interrupt mask/flag registers) */
+#define T16_INT_TOV    0x1 /* Timer overflow */
+#define T16_INT_OCA    0x2 /* Output compare A */
+#define T16_INT_OCB    0x4 /* Output compare B */
+#define T16_INT_OCC    0x8 /* Output compare C */
+#define T16_INT_IC     0x20 /* Input capture */
+
+/* Clock source values */
+#define T16_CLKSRC_STOPPED     0
+#define T16_CLKSRC_DIV1        1
+#define T16_CLKSRC_DIV8        2
+#define T16_CLKSRC_DIV64       3
+#define T16_CLKSRC_DIV256      4
+#define T16_CLKSRC_DIV1024     5
+#define T16_CLKSRC_EXT_FALLING 6
+#define T16_CLKSRC_EXT_RISING  7
+
+/* Timer mode values (not including PWM modes) */
+#define T16_MODE_NORMAL     0
+#define T16_MODE_CTC_OCRA   4
+#define T16_MODE_CTC_ICR    12
+
+/* Accessors */
+#define CLKSRC(t16) (t16->crb & T16_CRB_CS)
+#define MODE(t16)   (((t16->crb & T16_CRB_WGM23) >> 1) | \
+                     (t16->cra & T16_CRA_WGM01))
+#define CNT(t16)    VAL16(t16->cntl, t16->cnth)
+#define OCRA(t16)   VAL16(t16->ocral, t16->ocrah)
+#define OCRB(t16)   VAL16(t16->ocrbl, t16->ocrbh)
+#define OCRC(t16)   VAL16(t16->ocrcl, t16->ocrch)
+#define ICR(t16)    VAL16(t16->icrl, t16->icrh)
+
+/* Helper macros */
+#define VAL16(l, h) ((h << 8) | l)
+#define ERROR(fmt, args...) \
+    qemu_log_mask(LOG_GUEST_ERROR, "%s: " fmt "\n", __func__, ## args)
+#define DB_PRINT(fmt, args...) /* Nothing */
+/*#define DB_PRINT(fmt, args...) printf("%s: " fmt "\n", __func__, ## args)*/
+
+static inline int64_t avr_timer16_ns_to_ticks(AVRTimer16State *t16, int64_t t)
+{
+    if (t16->period_ns == 0) {
+        return 0;
+    }
+    return t / t16->period_ns;
+}
+
+static void avr_timer16_update_cnt(AVRTimer16State *t16)
+{
+    uint16_t cnt;
+    cnt = avr_timer16_ns_to_ticks(t16, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) -
+                                       t16->reset_time_ns);
+    t16->cntl = (uint8_t)(cnt & 0xff);
+    t16->cnth = (uint8_t)((cnt & 0xff00) >> 8);
+}
+
+static inline void avr_timer16_recalc_reset_time(AVRTimer16State *t16)
+{
+    t16->reset_time_ns = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) -
+                         CNT(t16) * t16->period_ns;
+}
+
+static void avr_timer16_clock_reset(AVRTimer16State *t16)
+{
+    t16->cntl = 0;
+    t16->cnth = 0;
+    t16->reset_time_ns = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
+}
+
+static void avr_timer16_clksrc_update(AVRTimer16State *t16)
+{
+    uint16_t divider = 0;
+    switch (CLKSRC(t16)) {
+    case T16_CLKSRC_EXT_FALLING:
+    case T16_CLKSRC_EXT_RISING:
+        ERROR("external clock source unsupported");
+        goto end;
+    case T16_CLKSRC_STOPPED:
+        goto end;
+    case T16_CLKSRC_DIV1:
+        divider = 1;
+        break;
+    case T16_CLKSRC_DIV8:
+        divider = 8;
+        break;
+    case T16_CLKSRC_DIV64:
+        divider = 64;
+        break;
+    case T16_CLKSRC_DIV256:
+        divider = 256;
+        break;
+    case T16_CLKSRC_DIV1024:
+        divider = 1024;
+        break;
+    default:
+        goto end;
+    }
+    t16->freq_hz = t16->cpu_freq_hz / divider;
+    t16->period_ns = NANOSECONDS_PER_SECOND / t16->freq_hz;
+    DB_PRINT("Timer frequency %" PRIu64 " hz, period %" PRIu64 " ns (%f s)",
+             t16->freq_hz, t16->period_ns, 1 / (double)t16->freq_hz);
+end:
+    return;
+}
+
+static void avr_timer16_set_alarm(AVRTimer16State *t16)
+{
+    if (CLKSRC(t16) == T16_CLKSRC_EXT_FALLING ||
+        CLKSRC(t16) == T16_CLKSRC_EXT_RISING ||
+        CLKSRC(t16) == T16_CLKSRC_STOPPED) {
+        /* Timer is disabled or set to external clock source (unsupported) */
+        goto end;
+    }
+
+    uint64_t alarm_offset = 0xffff;
+    enum NextInterrupt next_interrupt = OVERFLOW;
+
+    switch (MODE(t16)) {
+    case T16_MODE_NORMAL:
+        /* Normal mode */
+        if (OCRA(t16) < alarm_offset && OCRA(t16) > CNT(t16) &&
+            (t16->imsk & T16_INT_OCA)) {
+            alarm_offset = OCRA(t16);
+            next_interrupt = COMPA;
+        }
+        break;
+    case T16_MODE_CTC_OCRA:
+        /* CTC mode, top = ocra */
+        if (OCRA(t16) < alarm_offset && OCRA(t16) > CNT(t16)) {
+            alarm_offset = OCRA(t16);
+            next_interrupt = COMPA;
+        }
+       break;
+    case T16_MODE_CTC_ICR:
+        /* CTC mode, top = icr */
+        if (ICR(t16) < alarm_offset && ICR(t16) > CNT(t16)) {
+            alarm_offset = ICR(t16);
+            next_interrupt = CAPT;
+        }
+        if (OCRA(t16) < alarm_offset && OCRA(t16) > CNT(t16) &&
+            (t16->imsk & T16_INT_OCA)) {
+            alarm_offset = OCRA(t16);
+            next_interrupt = COMPA;
+        }
+        break;
+    default:
+        ERROR("pwm modes are unsupported");
+        goto end;
+    }
+    if (OCRB(t16) < alarm_offset && OCRB(t16) > CNT(t16) &&
+        (t16->imsk & T16_INT_OCB)) {
+        alarm_offset = OCRB(t16);
+        next_interrupt = COMPB;
+    }
+    if (OCRC(t16) < alarm_offset && OCRB(t16) > CNT(t16) &&
+        (t16->imsk & T16_INT_OCC)) {
+        alarm_offset = OCRB(t16);
+        next_interrupt = COMPC;
+    }
+    alarm_offset -= CNT(t16);
+
+    t16->next_interrupt = next_interrupt;
+    uint64_t alarm_ns =
+        t16->reset_time_ns + ((CNT(t16) + alarm_offset) * t16->period_ns);
+    timer_mod(t16->timer, alarm_ns);
+
+    DB_PRINT("next alarm %" PRIu64 " ns from now",
+        alarm_offset * t16->period_ns);
+
+end:
+    return;
+}
+
+static void avr_timer16_interrupt(void *opaque)
+{
+    AVRTimer16State *t16 = opaque;
+    uint8_t mode = MODE(t16);
+
+    avr_timer16_update_cnt(t16);
+
+    if (CLKSRC(t16) == T16_CLKSRC_EXT_FALLING ||
+        CLKSRC(t16) == T16_CLKSRC_EXT_RISING ||
+        CLKSRC(t16) == T16_CLKSRC_STOPPED) {
+        /* Timer is disabled or set to external clock source (unsupported) */
+        return;
+    }
+
+    DB_PRINT("interrupt, cnt = %d", CNT(t16));
+
+    /* Counter overflow */
+    if (t16->next_interrupt == OVERFLOW) {
+        DB_PRINT("0xffff overflow");
+        avr_timer16_clock_reset(t16);
+        if (t16->imsk & T16_INT_TOV) {
+            t16->ifr |= T16_INT_TOV;
+            qemu_set_irq(t16->ovf_irq, 1);
+        }
+    }
+    /* Check for ocra overflow in CTC mode */
+    if (mode == T16_MODE_CTC_OCRA && t16->next_interrupt == COMPA) {
+        DB_PRINT("CTC OCRA overflow");
+        avr_timer16_clock_reset(t16);
+    }
+    /* Check for icr overflow in CTC mode */
+    if (mode == T16_MODE_CTC_ICR && t16->next_interrupt == CAPT) {
+        DB_PRINT("CTC ICR overflow");
+        avr_timer16_clock_reset(t16);
+        if (t16->imsk & T16_INT_IC) {
+            t16->ifr |= T16_INT_IC;
+            qemu_set_irq(t16->capt_irq, 1);
+        }
+    }
+    /* Check for output compare interrupts */
+    if (t16->imsk & T16_INT_OCA && t16->next_interrupt == COMPA) {
+        t16->ifr |= T16_INT_OCA;
+        qemu_set_irq(t16->compa_irq, 1);
+    }
+    if (t16->imsk & T16_INT_OCB && t16->next_interrupt == COMPB) {
+        t16->ifr |= T16_INT_OCB;
+        qemu_set_irq(t16->compb_irq, 1);
+    }
+    if (t16->imsk & T16_INT_OCC && t16->next_interrupt == COMPC) {
+        t16->ifr |= T16_INT_OCC;
+        qemu_set_irq(t16->compc_irq, 1);
+    }
+    avr_timer16_set_alarm(t16);
+}
+
+static void avr_timer16_reset(DeviceState *dev)
+{
+    AVRTimer16State *t16 = AVR_TIMER16(dev);
+
+    avr_timer16_clock_reset(t16);
+    avr_timer16_clksrc_update(t16);
+    avr_timer16_set_alarm(t16);
+
+    qemu_set_irq(t16->capt_irq, 0);
+    qemu_set_irq(t16->compa_irq, 0);
+    qemu_set_irq(t16->compb_irq, 0);
+    qemu_set_irq(t16->compc_irq, 0);
+    qemu_set_irq(t16->ovf_irq, 0);
+}
+
+static uint64_t avr_timer16_read(void *opaque, hwaddr offset, unsigned size)
+{
+    assert(size == 1);
+    AVRTimer16State *t16 = opaque;
+    uint8_t retval = 0;
+
+    switch (offset) {
+    case T16_CRA:
+        retval = t16->cra;
+        break;
+    case T16_CRB:
+        retval = t16->crb;
+        break;
+    case T16_CRC:
+        retval = t16->crc;
+        break;
+    case T16_CNTL:
+        avr_timer16_update_cnt(t16);
+        t16->rtmp = t16->cnth;
+        retval = t16->cntl;
+        break;
+    case T16_CNTH:
+        retval = t16->rtmp;
+        break;
+    case T16_ICRL:
+        /*
+         * The timer copies cnt to icr when the input capture pin changes
+         * state or when the analog comparator has a match. We don't
+         * emulate this behaviour. We do support it's use for defining a
+         * TOP value in T16_MODE_CTC_ICR
+         */
+        t16->rtmp = t16->icrh;
+        retval = t16->icrl;
+        break;
+    case T16_ICRH:
+        retval = t16->rtmp;
+        break;
+    case T16_OCRAL:
+        retval = t16->ocral;
+        break;
+    case T16_OCRAH:
+        retval = t16->ocrah;
+        break;
+    case T16_OCRBL:
+        retval = t16->ocrbl;
+        break;
+    case T16_OCRBH:
+        retval = t16->ocrbh;
+        break;
+    case T16_OCRCL:
+        retval = t16->ocrcl;
+        break;
+    case T16_OCRCH:
+        retval = t16->ocrch;
+        break;
+    default:
+        break;
+    }
+    return (uint64_t)retval;
+}
+
+static void avr_timer16_write(void *opaque, hwaddr offset,
+                              uint64_t val64, unsigned size)
+{
+    assert(size == 1);
+    AVRTimer16State *t16 = opaque;
+    uint8_t val8 = (uint8_t)val64;
+    uint8_t prev_clk_src = CLKSRC(t16);
+
+    DB_PRINT("write %d to offset %d", val8, (uint8_t)offset);
+
+    switch (offset) {
+    case T16_CRA:
+        t16->cra = val8;
+        if (t16->cra & T16_CRA_OC_CONF) {
+            ERROR("output compare pins unsupported");
+        }
+        break;
+    case T16_CRB:
+        t16->crb = val8;
+        if (t16->crb & T16_CRB_ICNC) {
+            ERROR("input capture noise canceller unsupported");
+        }
+        if (t16->crb & T16_CRB_ICES) {
+            ERROR("input capture unsupported");
+        }
+        if (CLKSRC(t16) != prev_clk_src) {
+            avr_timer16_clksrc_update(t16);
+            if (prev_clk_src == T16_CLKSRC_STOPPED) {
+                t16->reset_time_ns = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
+            }
+        }
+        break;
+    case T16_CRC:
+        t16->crc = val8;
+        ERROR("output compare pins unsupported");
+        break;
+    case T16_CNTL:
+        /*
+         * CNT is the 16-bit counter value, it must be read/written via
+         * a temporary register (rtmp) to make the read/write atomic.
+         */
+        /* ICR also has this behaviour, and shares rtmp */
+        /*
+         * Writing CNT blocks compare matches for one clock cycle.
+         * Writing CNT to TOP or to an OCR value (if in use) will
+         * skip the relevant interrupt
+         */
+        t16->cntl = val8;
+        t16->cnth = t16->rtmp;
+        avr_timer16_recalc_reset_time(t16);
+        break;
+    case T16_CNTH:
+        t16->rtmp = val8;
+        break;
+    case T16_ICRL:
+        /* ICR can only be written in mode T16_MODE_CTC_ICR */
+        if (MODE(t16) == T16_MODE_CTC_ICR) {
+            t16->icrl = val8;
+            t16->icrh = t16->rtmp;
+        }
+        break;
+    case T16_ICRH:
+        if (MODE(t16) == T16_MODE_CTC_ICR) {
+            t16->rtmp = val8;
+        }
+        break;
+    case T16_OCRAL:
+        /*
+         * OCRn cause the relevant output compare flag to be raised, and
+         * trigger an interrupt, when CNT is equal to the value here
+         */
+        t16->ocral = val8;
+        break;
+    case T16_OCRAH:
+        t16->ocrah = val8;
+        break;
+    case T16_OCRBL:
+        t16->ocrbl = val8;
+        break;
+    case T16_OCRBH:
+        t16->ocrbh = val8;
+        break;
+    case T16_OCRCL:
+        t16->ocrcl = val8;
+        break;
+    case T16_OCRCH:
+        t16->ocrch = val8;
+        break;
+    default:
+        break;
+    }
+    avr_timer16_set_alarm(t16);
+}
+
+static uint64_t avr_timer16_imsk_read(void *opaque,
+                                      hwaddr offset,
+                                      unsigned size)
+{
+    assert(size == 1);
+    AVRTimer16State *t16 = opaque;
+    if (offset != 0) {
+        return 0;
+    }
+    return t16->imsk;
+}
+
+static void avr_timer16_imsk_write(void *opaque, hwaddr offset,
+                                   uint64_t val64, unsigned size)
+{
+    assert(size == 1);
+    AVRTimer16State *t16 = opaque;
+    if (offset != 0) {
+        return;
+    }
+    t16->imsk = (uint8_t)val64;
+}
+
+static uint64_t avr_timer16_ifr_read(void *opaque,
+                                     hwaddr offset,
+                                     unsigned size)
+{
+    assert(size == 1);
+    AVRTimer16State *t16 = opaque;
+    if (offset != 0) {
+        return 0;
+    }
+    return t16->ifr;
+}
+
+static void avr_timer16_ifr_write(void *opaque, hwaddr offset,
+                                  uint64_t val64, unsigned size)
+{
+    assert(size == 1);
+    AVRTimer16State *t16 = opaque;
+    if (offset != 0) {
+        return;
+    }
+    t16->ifr = (uint8_t)val64;
+}
+
+static const MemoryRegionOps avr_timer16_ops = {
+    .read = avr_timer16_read,
+    .write = avr_timer16_write,
+    .endianness = DEVICE_NATIVE_ENDIAN,
+    .impl = {.max_access_size = 1}
+};
+
+static const MemoryRegionOps avr_timer16_imsk_ops = {
+    .read = avr_timer16_imsk_read,
+    .write = avr_timer16_imsk_write,
+    .endianness = DEVICE_NATIVE_ENDIAN,
+    .impl = {.max_access_size = 1}
+};
+
+static const MemoryRegionOps avr_timer16_ifr_ops = {
+    .read = avr_timer16_ifr_read,
+    .write = avr_timer16_ifr_write,
+    .endianness = DEVICE_NATIVE_ENDIAN,
+    .impl = {.max_access_size = 1}
+};
+
+static Property avr_timer16_properties[] = {
+    DEFINE_PROP_UINT8("id", struct AVRTimer16State, id, 0),
+    DEFINE_PROP_UINT64("cpu-frequency-hz", struct AVRTimer16State,
+                       cpu_freq_hz, 20000000),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
+static void avr_timer16_pr(void *opaque, int irq, int level)
+{
+    AVRTimer16State *s = AVR_TIMER16(opaque);
+
+    s->enabled = !level;
+
+    if (!s->enabled) {
+        avr_timer16_reset(DEVICE(s));
+    }
+}
+
+static void avr_timer16_init(Object *obj)
+{
+    AVRTimer16State *s = AVR_TIMER16(obj);
+
+    sysbus_init_irq(SYS_BUS_DEVICE(obj), &s->capt_irq);
+    sysbus_init_irq(SYS_BUS_DEVICE(obj), &s->compa_irq);
+    sysbus_init_irq(SYS_BUS_DEVICE(obj), &s->compb_irq);
+    sysbus_init_irq(SYS_BUS_DEVICE(obj), &s->compc_irq);
+    sysbus_init_irq(SYS_BUS_DEVICE(obj), &s->ovf_irq);
+
+    memory_region_init_io(&s->iomem, obj, &avr_timer16_ops,
+                          s, "avr-timer16", 0xe);
+    memory_region_init_io(&s->imsk_iomem, obj, &avr_timer16_imsk_ops,
+                          s, "avr-timer16-intmask", 0x1);
+    memory_region_init_io(&s->ifr_iomem, obj, &avr_timer16_ifr_ops,
+                          s, "avr-timer16-intflag", 0x1);
+
+    sysbus_init_mmio(SYS_BUS_DEVICE(obj), &s->iomem);
+    sysbus_init_mmio(SYS_BUS_DEVICE(obj), &s->imsk_iomem);
+    sysbus_init_mmio(SYS_BUS_DEVICE(obj), &s->ifr_iomem);
+    qdev_init_gpio_in(DEVICE(s), avr_timer16_pr, 1);
+
+    s->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, avr_timer16_interrupt, s);
+    s->enabled = true;
+}
+
+static void avr_timer16_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+
+    dc->reset = avr_timer16_reset;
+    dc->props = avr_timer16_properties;
+}
+
+static const TypeInfo avr_timer16_info = {
+    .name          = TYPE_AVR_TIMER16,
+    .parent        = TYPE_SYS_BUS_DEVICE,
+    .instance_size = sizeof(AVRTimer16State),
+    .instance_init = avr_timer16_init,
+    .class_init    = avr_timer16_class_init,
+};
+
+static void avr_timer16_register_types(void)
+{
+    type_register_static(&avr_timer16_info);
+}
+
+type_init(avr_timer16_register_types)
diff --git a/hw/timer/Kconfig b/hw/timer/Kconfig
index 59b3f44d69..cc66b60ef1 100644
--- a/hw/timer/Kconfig
+++ b/hw/timer/Kconfig
@@ -35,3 +35,6 @@  config CMSDK_APB_TIMER
 config CMSDK_APB_DUALTIMER
     bool
     select PTIMER
+
+config ATMEL_TIMER16
+    bool
diff --git a/hw/timer/Makefile.objs b/hw/timer/Makefile.objs
index dece235fd7..08a8a5cee9 100644
--- a/hw/timer/Makefile.objs
+++ b/hw/timer/Makefile.objs
@@ -35,3 +35,5 @@  common-obj-$(CONFIG_CMSDK_APB_TIMER) += cmsdk-apb-timer.o
 common-obj-$(CONFIG_CMSDK_APB_DUALTIMER) += cmsdk-apb-dualtimer.o
 common-obj-$(CONFIG_MSF2) += mss-timer.o
 common-obj-$(CONFIG_RASPI) += bcm2835_systmr.o
+
+obj-$(CONFIG_ATMEL_TIMER16) += atmel_timer16.o