AS3525v1/2: Enable nested handling of interrupts

Mostly for the sake of reducing latency for audio servicing where other service
routines can take a long time to complete, leading to occasional drops of a
few samples, especially in recording, where they are fairly frequent.

One mystery that remains is GPIOA IRQ being interrupted causes strange
undefined instruction exceptions, most easily produced on my Fuze V2 with a
scrollwheel. Making GPIOA the top ISR for now, thus not interruptible, cures it.

SVC mode is used during the actual calls. Hopefully the SVC stack size is
sufficient. Prologue and epilogue code only uses the IRQ stack and is large
enough.

Any routine code that should not be interrupted should disable IRQ itself from
here on in.


git-svn-id: svn://svn.rockbox.org/rockbox/trunk@31642 a1c6a512-1295-4272-9138-f99709370657

8 files changed, 105 insertions, 48 deletions

diff --git a/firmware/kernel.c b/firmware/kernel.c
index 155205749f..0b39e29126 100644
--- a/firmware/kernel.c
+++ b/firmware/kernel.c
@@ -1195,9 +1195,7 @@ int semaphore_wait(struct semaphore *s, int timeout)
  * in 'semaphore_init'. */
 void semaphore_release(struct semaphore *s)
 {
-#if defined(HAVE_PRIORITY_SCHEDULING) && defined(irq_enabled_checkval)
     unsigned int result = THREAD_NONE;
-#endif
     int oldlevel;
 
     oldlevel = disable_irq_save();
@@ -1209,11 +1207,7 @@ void semaphore_release(struct semaphore *s)
         KERNEL_ASSERT(s->count == 0,
             "semaphore_release->threads queued but count=%d!\n", s->count);
         s->queue->retval = OBJ_WAIT_SUCCEEDED; /* indicate explicit wake */
-#if defined(HAVE_PRIORITY_SCHEDULING) && defined(irq_enabled_checkval)
         result = wakeup_thread(&s->queue);
-#else
-        wakeup_thread(&s->queue);
-#endif
     }
     else
     {
@@ -1228,11 +1222,11 @@ void semaphore_release(struct semaphore *s)
     corelock_unlock(&s->cl);
     restore_irq(oldlevel);
 
-#if defined(HAVE_PRIORITY_SCHEDULING) && defined(irq_enabled_checkval)
-    /* No thread switch if IRQ disabled - it's probably called via ISR.
-     * switch_thread would as well enable them anyway. */
-    if((result & THREAD_SWITCH) && irq_enabled_checkval(oldlevel))
+#if defined(HAVE_PRIORITY_SCHEDULING) && defined(is_thread_context)
+    /* No thread switch if not thread context */
+    if((result & THREAD_SWITCH) && is_thread_context())
         switch_thread();
 #endif
+    (void)result;
 }
 #endif /* HAVE_SEMAPHORE_OBJECTS */
diff --git a/firmware/target/arm/as3525/fmradio-i2c-as3525.c b/firmware/target/arm/as3525/fmradio-i2c-as3525.c
index 3da42e31b2..5d05956799 100644
--- a/firmware/target/arm/as3525/fmradio-i2c-as3525.c
+++ b/firmware/target/arm/as3525/fmradio-i2c-as3525.c
@@ -195,8 +195,8 @@ void tuner_isr(void)
     /* read and clear the interrupt */
     if (GPIOA_MIS & (1<<4)) {
         semaphore_release(&rds_sema);
+        GPIOA_IC = (1<<4);
     }
-    GPIOA_IC = (1<<4);
 }
 
 /* Captures RDS data and processes it */
diff --git a/firmware/target/arm/as3525/sansa-fuzev2/button-fuzev2.c b/firmware/target/arm/as3525/sansa-fuzev2/button-fuzev2.c
index 7f82b692c7..8244c475fa 100644
--- a/firmware/target/arm/as3525/sansa-fuzev2/button-fuzev2.c
+++ b/firmware/target/arm/as3525/sansa-fuzev2/button-fuzev2.c
@@ -30,6 +30,7 @@ static bool hold_button = false;
 
 #ifdef HAVE_SCROLLWHEEL
 #define SCROLLWHEEL_BITS        (1<<7|1<<6)
+#define SCROLLWHEEL_BITS_POS    6
                                                       /* TIMER units */
 #define TIMER_TICK              (KERNEL_TIMER_FREQ/HZ)/* how long a tick lasts */
 #define TIMER_MS                (TIMER_TICK/(1000/HZ))/* how long a ms lasts */
@@ -78,10 +79,17 @@ static void scrollwheel(unsigned int wheel_value)
 
     unsigned int btn = BUTTON_NONE;
 
-    if (old_wheel_value == wheel_tbl[0][wheel_value])
+    if (hold_button)
+    {
+    }
+    else if (old_wheel_value == wheel_tbl[0][wheel_value])
+    {
         btn = BUTTON_SCROLL_FWD;
+    }
     else if (old_wheel_value == wheel_tbl[1][wheel_value])
+    {
         btn = BUTTON_SCROLL_BACK;
+    }
 
     if (btn == BUTTON_NONE)
     {
@@ -200,11 +208,13 @@ void button_gpioa_isr(void)
 {
 #if defined(HAVE_SCROLLWHEEL)
     /* scroll wheel handling */
-    if (GPIOA_MIS & SCROLLWHEEL_BITS)
-        scrollwheel(GPIOA_PIN_MASK(0xc0) >> 6);
+    unsigned long bits = GPIOA_MIS & SCROLLWHEEL_BITS;
 
-    /* ack interrupt */
-    GPIOA_IC = SCROLLWHEEL_BITS;
+    if (bits)
+    {
+        scrollwheel(GPIOA_PIN_MASK(SCROLLWHEEL_BITS) >> SCROLLWHEEL_BITS_POS);
+        GPIOA_IC = bits; /* ack interrupt */
+    }
 #endif
 }
 
@@ -225,8 +235,10 @@ int button_read_device(void)
     int delay = 30;
     while(delay--) nop;
 
+    disable_irq();
+
     bool ccu_io_bit12 = CCU_IO & (1<<12);
-    bitclr32(&CCU_IO, 1<<12);
+    CCU_IO &= ~(1<<12);
 
     /* B1 is shared with FM i2c */
     bool gpiob_pin0_dir = GPIOB_DIR & (1<<1);
@@ -256,7 +268,9 @@ int button_read_device(void)
         GPIOB_DIR |= 1<<1;
 
     if(ccu_io_bit12)
-        bitset32(&CCU_IO, 1<<12);
+        CCU_IO |= (1<<12);
+
+    enable_irq();
 
 #ifdef HAS_BUTTON_HOLD
 #ifndef BOOTLOADER
@@ -265,12 +279,6 @@ int button_read_device(void)
     {
         hold_button = hold;
         backlight_hold_changed(hold);
-        /* mask scrollwheel irq so we don't need to check for
-         * the hold button in the isr */
-        if (hold)
-            GPIOA_IE &= ~SCROLLWHEEL_BITS;
-        else
-            GPIOA_IE |= SCROLLWHEEL_BITS;
     }
 #else
     hold_button = hold;
diff --git a/firmware/target/arm/as3525/sd-as3525.c b/firmware/target/arm/as3525/sd-as3525.c
index 17f1bfa11d..5bed36e51e 100644
--- a/firmware/target/arm/as3525/sd-as3525.c
+++ b/firmware/target/arm/as3525/sd-as3525.c
@@ -178,10 +178,12 @@ static int sd1_oneshot_callback(struct timeout *tmo)
 void sd_gpioa_isr(void)
 {
     static struct timeout sd1_oneshot;
+
     if (GPIOA_MIS & EXT_SD_BITS)
+    {
         timeout_register(&sd1_oneshot, sd1_oneshot_callback, (3*HZ/10), 0);
-    /* acknowledge interrupt */
-    GPIOA_IC = EXT_SD_BITS;
+        GPIOA_IC = EXT_SD_BITS; /* acknowledge interrupt */
+    }
 }
 #endif  /* HAVE_HOTSWAP */
 
diff --git a/firmware/target/arm/as3525/sd-as3525v2.c b/firmware/target/arm/as3525/sd-as3525v2.c
index 717d5dd744..9edc598edf 100644
--- a/firmware/target/arm/as3525/sd-as3525v2.c
+++ b/firmware/target/arm/as3525/sd-as3525v2.c
@@ -1041,10 +1041,12 @@ static int sd1_oneshot_callback(struct timeout *tmo)
 void sd_gpioa_isr(void)
 {
     static struct timeout sd1_oneshot;
+
     if (GPIOA_MIS & EXT_SD_BITS)
+    {
         timeout_register(&sd1_oneshot, sd1_oneshot_callback, (3*HZ/10), 0);
-    /* acknowledge interrupt */
-    GPIOA_IC = EXT_SD_BITS;
+        GPIOA_IC = EXT_SD_BITS; /* acknowledge interrupt */
+    }
 }
 #endif /* HAVE_HOTSWAP */
 
diff --git a/firmware/target/arm/as3525/system-as3525.c b/firmware/target/arm/as3525/system-as3525.c
index 01aaeaccbe..f0ed75d2bd 100644
--- a/firmware/target/arm/as3525/system-as3525.c
+++ b/firmware/target/arm/as3525/system-as3525.c
@@ -51,7 +51,7 @@
   extern __attribute__((weak,alias("UIRQ"))) void name (void)
 
 static void UIRQ (void) __attribute__((interrupt ("IRQ")));
-void irq_handler(void) __attribute__((interrupt ("IRQ")));
+void irq_handler(void) __attribute__((naked, interrupt ("IRQ")));
 void fiq_handler(void) __attribute__((interrupt ("FIQ")));
 
 default_interrupt(INT_WATCHDOG);
@@ -121,6 +121,11 @@ static void UIRQ(void)
 static const struct { int source; void (*isr) (void); } vec_int_srcs[] =
 {
     /* Highest priority at the top of the list */
+#if defined(HAVE_HOTSWAP) || defined(HAVE_RDS_CAP) || \
+    (defined(SANSA_FUZEV2) && !INCREASED_SCROLLWHEEL_POLLING)
+    /* If GPIOA ISR is interrupted, things seem to go wonky ?? */
+    { INT_SRC_GPIOA, INT_GPIOA },
+#endif
 #ifdef HAVE_RECORDING
     { INT_SRC_I2SIN, INT_I2SIN }, /* For recording */
 #endif
@@ -134,29 +139,26 @@ static const struct { int source; void (*isr) (void); } vec_int_srcs[] =
     { INT_SRC_TIMER2, INT_TIMER2 },
     { INT_SRC_I2C_AUDIO, INT_I2C_AUDIO },
     { INT_SRC_AUDIO, INT_AUDIO },
-#if defined(HAVE_HOTSWAP) || \
-    (defined(SANSA_FUZEV2) && !INCREASED_SCROLLWHEEL_POLLING)
-    { INT_SRC_GPIOA, INT_GPIOA, },
-#endif
     /* Lowest priority at the end of the list */
 };
 
 static void setup_vic(void)
 {
-    const unsigned int n = sizeof(vec_int_srcs)/sizeof(vec_int_srcs[0]);
-    unsigned int i;
-
     CGU_PERI |= CGU_VIC_CLOCK_ENABLE; /* enable VIC */
     VIC_INT_EN_CLEAR = 0xffffffff; /* disable all interrupt lines */
     VIC_INT_SELECT = 0; /* only IRQ, no FIQ */
 
     *VIC_DEF_VECT_ADDR = UIRQ;
 
-    for(i = 0; i < n; i++)
+    for(unsigned int i = 0; i < ARRAYLEN(vec_int_srcs); i++)
     {
         VIC_VECT_ADDRS[i] = vec_int_srcs[i].isr;
         VIC_VECT_CNTLS[i] = (1<<5) | vec_int_srcs[i].source;
     }
+
+    /* Reset priority hardware */
+    for(unsigned int i = 0; i < 32; i++)
+        *VIC_VECT_ADDR = 0;
 }
 
 void INT_GPIOA(void)
@@ -177,8 +179,36 @@ void INT_GPIOA(void)
 
 void irq_handler(void)
 {
-    (*VIC_VECT_ADDR)(); /* call the isr */
-    *VIC_VECT_ADDR = (void*)VIC_VECT_ADDR; /* any write will ack the irq */
+    /* Worst-case IRQ stack usage with 10 vectors:
+     * 10*4*10 = 400 bytes (100 words)
+     *
+     * No SVC stack is used by pro/epi-logue code
+     */
+    asm volatile (
+        "sub    lr, lr, #4               \n" /* Create return address */
+        "stmfd  sp!, { r0-r5, r12, lr }  \n" /* Save what gets clobbered */
+        "ldr    r0, =0xc6010030          \n" /* Obtain VIC address (before SPSR read!) */
+        "ldr    r12, [r0]                \n" /* Load Vector */
+        "mrs    r1, spsr                 \n" /* Save SPSR_irq */
+        "stmfd  sp!, { r0-r1 }           \n" /* Must have something bet. mrs and msr */
+        "msr    cpsr_c, #0x13            \n" /* Switch to SVC mode, enable IRQ */
+        "and    r4, sp, #4               \n" /* Align SVC stack to 8 bytes, save */
+        "sub    sp, sp, r4               \n"
+        "mov    r5, lr                   \n" /* Save lr_SVC */
+#if ARM_ARCH >= 5
+        "blx    r12                      \n" /* Call handler */
+#else
+        "mov    lr, pc                   \n"
+        "bx     r12                      \n"
+#endif
+        "add    sp, sp, r4               \n" /* Undo alignment fudge */
+        "mov    lr, r5                   \n" /* Restore lr_SVC */
+        "msr    cpsr_c, #0x92            \n" /* Mask IRQ, return to IRQ mode */
+        "ldmfd  sp!, { r0-r1 }           \n" /* Pop VIC address, SPSR_irq */
+        "str    r0, [r0]                 \n" /* Ack end of ISR to VIC  */
+        "msr    spsr_cxsf, r1            \n" /* Restore SPSR_irq */
+        "ldmfd  sp!, { r0-r5, r12, pc }^ \n" /* Restore regs, and RFE */
+    );
 }
 
 void fiq_handler(void)
diff --git a/firmware/target/arm/crt0.S b/firmware/target/arm/crt0.S
index f75f37006d..7befecb593 100644
--- a/firmware/target/arm/crt0.S
+++ b/firmware/target/arm/crt0.S
@@ -100,17 +100,23 @@ newstart:
     strhi   r4, [r2], #4
     bhi     1b
 
-    /* Set up stack for IRQ mode */ 
+    /* Set up stack for IRQ mode */
     msr     cpsr_c, #0xd2
     ldr     sp, =irq_stack
 
-    /* Set up stack for FIQ mode */ 
-    msr     cpsr_c, #0xd1
-    ldr     sp, =fiq_stack
-
-    /* Let svc, abort and undefined modes use irq stack */
     msr     cpsr_c, #0xd3
+#if CONFIG_CPU == AS3525 || CONFIG_CPU == AS3525v2
+    /* Let abort and undefined modes use irq stack */
+    /* svc stack is for interrupt processing */
+    ldr     sp, =svc_stack
+#else
+    /* Let svc, abort and undefined modes use irq stack */
     ldr     sp, =irq_stack
+
+    /* Set up stack for FIQ mode */
+    msr     cpsr_c, #0xd1
+    ldr     sp, =fiq_stack
+#endif
     msr     cpsr_c, #0xd7
     ldr     sp, =irq_stack
     msr     cpsr_c, #0xdb
@@ -159,15 +165,20 @@ prefetch_abort_handler:
     b      UIE
 
 data_abort_handler:
-    sub    r0, lr, #8 
+    sub    r0, lr, #8
     mov    r1, #2
     b      UIE
 
+/* Cache-align interrupt stacks */
+.balign    32
+
 /* 256 words of IRQ stack */
     .space 256*4
 irq_stack:
 
-/* 256 words of FIQ stack */
+/* 256 words of FIQ/SVC stack */
     .space 256*4
 fiq_stack:
-end:
+svc_stack:
+
+end:
\ No newline at end of file
diff --git a/firmware/target/arm/system-arm.h b/firmware/target/arm/system-arm.h
index b3630a8473..ffce77a176 100644
--- a/firmware/target/arm/system-arm.h
+++ b/firmware/target/arm/system-arm.h
@@ -76,6 +76,9 @@ void __div0(void);
 #define ints_enabled_checkval(val) \
     (((val) & IRQ_FIQ_STATUS) == 0)
 
+/* We run in SYS mode */
+#define is_thread_context() \
+    (get_processor_mode() == 0x1f)
 
 /* Core-level interrupt masking */
 
@@ -109,6 +112,13 @@ static inline bool interrupt_enabled(int status)
     return (cpsr & status) == 0;
 }
 
+static inline unsigned long get_processor_mode(void)
+{
+    unsigned long cpsr;
+    asm ("mrs %0, cpsr" : "=r"(cpsr));
+    return cpsr & 0x1f;
+}
+
 /* ARM_ARCH version section for architecture*/
 
 #if ARM_ARCH >= 6