Merge pull request #6048 from OpenNuvoton/nuvoton_ticker

Nuvoton: Rework us_ticker and lp_ticker

Author: cmonr

targets/TARGET_NUVOTON/TARGET_M451/lp_ticker.c

@@ -13,37 +13,38 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
- 
+
 #include "lp_ticker_api.h"
 
 #if DEVICE_LOWPOWERTIMER
 
 #include "sleep_api.h"
+#include "mbed_wait_api.h"
+#include "mbed_assert.h"
 #include "nu_modutil.h"
 #include "nu_miscutil.h"
-#include "mbed_critical.h"
-
-// lp_ticker tick = us = timestamp
-#define US_PER_TICK             (1)
-#define US_PER_SEC              (1000 * 1000)
 
-#define US_PER_TMR2_INT         (US_PER_SEC * 10)
-#define TMR2_CLK_PER_SEC        (__LXT)
-#define TMR2_CLK_PER_TMR2_INT   ((uint32_t) ((uint64_t) US_PER_TMR2_INT * TMR2_CLK_PER_SEC / US_PER_SEC))
-#define TMR3_CLK_PER_SEC        (__LXT)
+/* Micro seconds per second */
+#define NU_US_PER_SEC               1000000
+/* Timer clock per lp_ticker tick */
+#define NU_TMRCLK_PER_TICK          1
+/* Timer clock per second */
+#define NU_TMRCLK_PER_SEC           (__LXT)
+/* Timer max counter bit size */
+#define NU_TMR_MAXCNT_BITSIZE       24
+/* Timer max counter */
+#define NU_TMR_MAXCNT               ((1 << NU_TMR_MAXCNT_BITSIZE) - 1)
 
 static void tmr2_vec(void);
 static void tmr3_vec(void);
-static void lp_ticker_arm_cd(void);
+/* Configure scheduled alarm */
+static void arm_alarm(uint32_t cd_clk);
 
-static int lp_ticker_inited = 0;
-static volatile uint32_t counter_major = 0;
-static volatile uint32_t cd_major_minor_clks = 0;
-static volatile uint32_t cd_minor_clks = 0;
-static volatile uint32_t wakeup_tick = (uint32_t) -1;
+static int ticker_inited = 0;
+static uint32_t ticker_last_read_clk = 0;
 
-// NOTE: To wake the system from power down mode, timer clock source must be ether LXT or LIRC.
-// NOTE: TIMER_2 for normal counting and TIMER_3 for scheduled wakeup
+/* NOTE: To wake the system from power down mode, timer clock source must be ether LXT or LIRC. */
+/* NOTE: TIMER_2 for normal counting and TIMER_3 for scheduled alarm */
 static const struct nu_modinit_s timer2_modinit = {TIMER_2, TMR2_MODULE, CLK_CLKSEL1_TMR2SEL_LXT, 0, TMR2_RST, TMR2_IRQn, (void *) tmr2_vec};
 static const struct nu_modinit_s timer3_modinit = {TIMER_3, TMR3_MODULE, CLK_CLKSEL1_TMR3SEL_LXT, 0, TMR3_RST, TMR3_IRQn, (void *) tmr3_vec};
 
@@ -52,20 +53,17 @@ static const struct nu_modinit_s timer3_modinit = {TIMER_3, TMR3_MODULE, CLK_CLK
 
 void lp_ticker_init(void)
 {
-    if (lp_ticker_inited) {
+    if (ticker_inited) {
         return;
     }
-    lp_ticker_inited = 1;
-    
-    counter_major = 0;
-    cd_major_minor_clks = 0;
-    cd_minor_clks = 0;
-    wakeup_tick = (uint32_t) -1;
+    ticker_inited = 1;
+
+    ticker_last_read_clk = 0;
 
     // Reset module
     SYS_ResetModule(timer2_modinit.rsetidx);
     SYS_ResetModule(timer3_modinit.rsetidx);
-    
+
     // Select IP clock source
     CLK_SetModuleClock(timer2_modinit.clkidx, timer2_modinit.clksrc, timer2_modinit.clkdiv);
     CLK_SetModuleClock(timer3_modinit.clkidx, timer3_modinit.clksrc, timer3_modinit.clkdiv);
@@ -75,93 +73,114 @@ void lp_ticker_init(void)
 
     // Configure clock
     uint32_t clk_timer2 = TIMER_GetModuleClock((TIMER_T *) NU_MODBASE(timer2_modinit.modname));
-    uint32_t prescale_timer2 = clk_timer2 / TMR2_CLK_PER_SEC - 1;
+    uint32_t prescale_timer2 = clk_timer2 / NU_TMRCLK_PER_SEC - 1;
     MBED_ASSERT((prescale_timer2 != (uint32_t) -1) && prescale_timer2 <= 127);
-    MBED_ASSERT((clk_timer2 % TMR2_CLK_PER_SEC) == 0);
-    uint32_t cmp_timer2 = TMR2_CLK_PER_TMR2_INT;
+    MBED_ASSERT((clk_timer2 % NU_TMRCLK_PER_SEC) == 0);
+    uint32_t cmp_timer2 = TMR_CMP_MAX;
     MBED_ASSERT(cmp_timer2 >= TMR_CMP_MIN && cmp_timer2 <= TMR_CMP_MAX);
     // Continuous mode
     // NOTE: TIMER_CTL_CNTDATEN_Msk exists in NUC472, but not in M451. In M451, TIMER_CNT is updated continuously by default.
     ((TIMER_T *) NU_MODBASE(timer2_modinit.modname))->CTL = TIMER_PERIODIC_MODE | prescale_timer2/* | TIMER_CTL_CNTDATEN_Msk*/;
     ((TIMER_T *) NU_MODBASE(timer2_modinit.modname))->CMP = cmp_timer2;
-    
+
     // Set vector
     NVIC_SetVector(timer2_modinit.irq_n, (uint32_t) timer2_modinit.var);
     NVIC_SetVector(timer3_modinit.irq_n, (uint32_t) timer3_modinit.var);
-    
+
     NVIC_EnableIRQ(timer2_modinit.irq_n);
     NVIC_EnableIRQ(timer3_modinit.irq_n);
-    
+
     TIMER_EnableInt((TIMER_T *) NU_MODBASE(timer2_modinit.modname));
     TIMER_EnableWakeup((TIMER_T *) NU_MODBASE(timer2_modinit.modname));
-    
-    // NOTE: TIMER_Start() first and then lp_ticker_set_interrupt(); otherwise, we may get stuck in lp_ticker_read() because
-    //       timer is not running.
-    
-    // Start timer
+    /* NOTE: When engine is clocked by low power clock source (LXT/LIRC), we need to wait for 3 engine clocks. */
+    wait_us((NU_US_PER_SEC / NU_TMRCLK_PER_SEC) * 3);
     TIMER_Start((TIMER_T *) NU_MODBASE(timer2_modinit.modname));
-    
-    // Schedule wakeup to match semantics of lp_ticker_get_compare_match()
-    lp_ticker_set_interrupt(wakeup_tick);
 }
 
 timestamp_t lp_ticker_read()
-{    
-    if (! lp_ticker_inited) {
+{
+    if (! ticker_inited) {
         lp_ticker_init();
     }
-    
+
     TIMER_T * timer2_base = (TIMER_T *) NU_MODBASE(timer2_modinit.modname);
-    
-    do {
-        uint64_t major_minor_clks;
-        uint32_t minor_clks;
-        
-        // NOTE: As TIMER_CNT = TIMER_CMP and counter_major has increased by one, TIMER_CNT doesn't change to 0 for one tick time.
-        // NOTE: As TIMER_CNT = TIMER_CMP or TIMER_CNT = 0, counter_major (ISR) may not sync with TIMER_CNT. So skip and fetch stable one at the cost of 1 clock delay on this read.
-        do {
-            core_util_critical_section_enter();
-        
-            // NOTE: Order of reading minor_us/carry here is significant.
-            minor_clks = TIMER_GetCounter(timer2_base);
-            uint32_t carry = (timer2_base->INTSTS & TIMER_INTSTS_TIF_Msk) ? 1 : 0;
-            // When TIMER_CNT approaches TIMER_CMP and will wrap soon, we may get carry but TIMER_CNT not wrapped. Hanlde carefully carry == 1 && TIMER_CNT is near TIMER_CMP.
-            if (carry && minor_clks > (TMR2_CLK_PER_TMR2_INT / 2)) {
-                major_minor_clks = (counter_major + 1) * TMR2_CLK_PER_TMR2_INT;
-            }
-            else {
-                major_minor_clks = (counter_major + carry) * TMR2_CLK_PER_TMR2_INT + minor_clks;
-            }
-            
-            core_util_critical_section_exit();
-        }
-        while (minor_clks == 0 || minor_clks == TMR2_CLK_PER_TMR2_INT);
-
-        // Add power-down compensation
-        return ((uint64_t) major_minor_clks * US_PER_SEC / TMR2_CLK_PER_SEC / US_PER_TICK);
-    }
-    while (0);
+
+    ticker_last_read_clk = TIMER_GetCounter(timer2_base);
+    return  (ticker_last_read_clk / NU_TMRCLK_PER_TICK);
 }
 
 void lp_ticker_set_interrupt(timestamp_t timestamp)
 {
-    uint32_t delta = timestamp - lp_ticker_read();
-    wakeup_tick = timestamp;
-    
     TIMER_Stop((TIMER_T *) NU_MODBASE(timer3_modinit.modname));
+
+    /* We need to get alarm interval from alarm timestamp `timestamp` to configure H/W timer.
+     *  
+     * Because both `timestamp` and xx_ticker_read() would wrap around, we have difficulties in distinguishing
+     * long future event and past event. To distinguish them, we need `tick_last_read` against which 
+     * `timestamp` is calculated out. In timeline, we would always have below after fixing wrap-around:
+     * (1) tick_last_read <= present_clk
+     * (2) tick_last_read <= alarm_ts_clk
+     *
+     *
+     * 1. Future event case:
+     *
+     * tick_last_read     present_clk                         alarm_ts_clk
+     * |                  |                                   |
+     * --------------------------------------------------------
+     * |-alarm_intvl1_clk-|
+     * |-------------------alarm_intvl2_clk-------------------|
+     *
+     * 2. Past event case:
+     *
+     * tick_last_read     alarm_ts_clk                        present_clk
+     * |                  |                                   |
+     * --------------------------------------------------------
+     * |-------------------alarm_intvl1_clk-------------------|
+     * |-alarm_intvl2_clk-|
+     *
+     * Unfortunately, `tick_last_read` is not passed along the xx_ticker_set_interrupt() call. To solve it, we
+     * assume that `tick_last_read` tick is exactly the one returned by the last xx_ticker_read() call before
+     * xx_ticker_set_interrupt() is invoked. With this assumption, we can hold it via `xx_ticker_last_read_clk`
+     * in xx_ticker_read().
+     */
+     
+    /* ticker_last_read_clk will update in lp_ticker_read(). Keep it beforehand. */
+    uint32_t last_read_clk = ticker_last_read_clk;
+    uint32_t present_clk = lp_ticker_read() * NU_TMRCLK_PER_TICK;
+    uint32_t alarm_ts_clk = timestamp * NU_TMRCLK_PER_TICK;
+    uint32_t alarm_intvl1_clk, alarm_intvl2_clk;
 
-    cd_major_minor_clks = (uint64_t) delta * US_PER_TICK * TMR3_CLK_PER_SEC / US_PER_SEC;
-    lp_ticker_arm_cd();
-}
+    /* alarm_intvl1_clk = present_clk - last_read_clk
+     *
+     * NOTE: Don't miss the `=` sign here. Otherwise, we would get the wrong result.
+     */
+    if (present_clk >= last_read_clk) {
+        alarm_intvl1_clk = present_clk - last_read_clk;
+    } else {
+        alarm_intvl1_clk = (uint32_t) (((uint64_t) NU_TMR_MAXCNT) + 1 + present_clk - last_read_clk);
+    }
 
-void lp_ticker_fire_interrupt(void)
-{
-    cd_major_minor_clks = cd_minor_clks = 0;
-    /**
-     * This event was in the past. Set the interrupt as pending, but don't process it here.
-     * This prevents a recurive loop under heavy load which can lead to a stack overflow.
-     */  
-    NVIC_SetPendingIRQ(timer3_modinit.irq_n);
+    /* alarm_intvl2_clk = alarm_ts_clk - last_read_clk
+     * 
+     * NOTE: Don't miss the `=` sign here. Otherwise, we would get the wrong result.
+     */
+    if (alarm_ts_clk >= last_read_clk) {
+        alarm_intvl2_clk = alarm_ts_clk - last_read_clk;
+    } else {
+        alarm_intvl2_clk = (uint32_t) (((uint64_t) NU_TMR_MAXCNT) + 1 + alarm_ts_clk - last_read_clk);
+    }
+
+    /* Distinguish (long) future event and past event
+     * 
+     * NOTE: No '=' sign here. Alarm should go off immediately in equal case.
+     */
+    if (alarm_intvl2_clk > alarm_intvl1_clk) {
+        /* Schedule for future event */
+        arm_alarm(alarm_intvl2_clk - alarm_intvl1_clk);
+    } else {
+        /* Go off immediately for past event, including equal case */
+        lp_ticker_fire_interrupt();
+    }
 }
 
 void lp_ticker_disable_interrupt(void)
@@ -174,48 +193,64 @@ void lp_ticker_clear_interrupt(void)
     TIMER_ClearIntFlag((TIMER_T *) NU_MODBASE(timer3_modinit.modname));
 }
 
+void lp_ticker_fire_interrupt(void)
+{
+    // NOTE: This event was in the past. Set the interrupt as pending, but don't process it here.
+    //       This prevents a recursive loop under heavy load which can lead to a stack overflow.
+    NVIC_SetPendingIRQ(timer3_modinit.irq_n);
+}
+
 static void tmr2_vec(void)
 {
     TIMER_ClearIntFlag((TIMER_T *) NU_MODBASE(timer2_modinit.modname));
     TIMER_ClearWakeupFlag((TIMER_T *) NU_MODBASE(timer2_modinit.modname));
-    counter_major ++;
 }
 
 static void tmr3_vec(void)
 {
     TIMER_ClearIntFlag((TIMER_T *) NU_MODBASE(timer3_modinit.modname));
     TIMER_ClearWakeupFlag((TIMER_T *) NU_MODBASE(timer3_modinit.modname));
-    cd_major_minor_clks = (cd_major_minor_clks > cd_minor_clks) ? (cd_major_minor_clks - cd_minor_clks) : 0;
-    if (cd_major_minor_clks == 0) {
-        // NOTE: lp_ticker_set_interrupt() may get called in lp_ticker_irq_handler();
-        lp_ticker_irq_handler();
-    }
-    else {
-        lp_ticker_arm_cd();
-    }
+
+    // NOTE: lp_ticker_set_interrupt() may get called in lp_ticker_irq_handler();
+    lp_ticker_irq_handler();
+    
 }
 
-static void lp_ticker_arm_cd(void)
+static void arm_alarm(uint32_t cd_clk)
 {
     TIMER_T * timer3_base = (TIMER_T *) NU_MODBASE(timer3_modinit.modname);
-    
+
     // Reset 8-bit PSC counter, 24-bit up counter value and CNTEN bit
     timer3_base->CTL |= TIMER_CTL_RSTCNT_Msk;
     // One-shot mode, Clock = 1 KHz 
     uint32_t clk_timer3 = TIMER_GetModuleClock((TIMER_T *) NU_MODBASE(timer3_modinit.modname));
-    uint32_t prescale_timer3 = clk_timer3 / TMR3_CLK_PER_SEC - 1;
+    uint32_t prescale_timer3 = clk_timer3 / NU_TMRCLK_PER_SEC - 1;
     MBED_ASSERT((prescale_timer3 != (uint32_t) -1) && prescale_timer3 <= 127);
-    MBED_ASSERT((clk_timer3 % TMR3_CLK_PER_SEC) == 0);
+    MBED_ASSERT((clk_timer3 % NU_TMRCLK_PER_SEC) == 0);
     // NOTE: TIMER_CTL_CNTDATEN_Msk exists in NUC472, but not in M451. In M451, TIMER_CNT is updated continuously by default.
     timer3_base->CTL &= ~(TIMER_CTL_OPMODE_Msk | TIMER_CTL_PSC_Msk/* | TIMER_CTL_CNTDATEN_Msk*/);
     timer3_base->CTL |= TIMER_ONESHOT_MODE | prescale_timer3/* | TIMER_CTL_CNTDATEN_Msk*/;
-    
-    cd_minor_clks = cd_major_minor_clks;
-    cd_minor_clks = NU_CLAMP(cd_minor_clks, TMR_CMP_MIN, TMR_CMP_MAX);
-    timer3_base->CMP = cd_minor_clks;
-    
+
+    /* NOTE: Because H/W timer requests min compare value, our implementation would have alarm delay of 
+     *       (TMR_CMP_MIN - interval_clk) clocks when interval_clk is between [1, TMR_CMP_MIN). */
+    uint32_t cmp_timer3 = cd_clk;
+    cmp_timer3 = NU_CLAMP(cmp_timer3, TMR_CMP_MIN, TMR_CMP_MAX);
+    timer3_base->CMP = cmp_timer3;
+
     TIMER_EnableInt(timer3_base);
     TIMER_EnableWakeup((TIMER_T *) NU_MODBASE(timer3_modinit.modname));
+    /* NOTE: When engine is clocked by low power clock source (LXT/LIRC), we need to wait for 3 engine clocks. */
+    wait_us((NU_US_PER_SEC / NU_TMRCLK_PER_SEC) * 3);
     TIMER_Start(timer3_base);
 }
+
+const ticker_info_t* lp_ticker_get_info()
+{
+    static const ticker_info_t info = {
+        NU_TMRCLK_PER_SEC / NU_TMRCLK_PER_TICK,
+        NU_TMR_MAXCNT_BITSIZE
+    };
+    return &info;
+}
+
 #endif