baremetal aarch64: timer.c get closer to working

Author: cirosantilli

README.adoc

@@ -14156,6 +14156,15 @@ TODO: create and study a minimal examples in gem5 where the DMB instruction lead
 
 TODO get working. Attempt at: link:baremetal/arch/aarch64/timer.c[]
 
+The timer is documented at: <<armarm8-db>> Chapter D10 "The Generic Timer in AArch64 state"
+
+The key registers to keep in mind are:
+
+* `CNTVCT_EL0`: "Counter-timer Virtual Count register". The increasing current counter value.
+* `CNTFRQ_EL0`: "Counter-timer Frequency register". "Indicates the system counter clock frequency, in Hz."
+* `CNTV_CTL_EL0`: "Counter-timer Virtual Timer Control register"
+* `CNTV_CVAL_EL0`: "Counter-timer Virtual Timer CompareValue register". The interrupt happens when `CNTVCT_EL0` reaches the value in this register.
+
 ==== ARM baremetal bibliography
 
 First, also consider the userland bibliography: <<arm-assembly-bibliography>>.
@@ -14208,7 +14217,7 @@ which further confirms that the exception is correct: v2 has a register range at
 
 The original source does not mention GICv3 anywhere, only link:https://github.com/takeharukato/sample-tsk-sw/blob/c7bbc9dce6b14660bcce8d20735f8c6ebb09396b/hal/aarch64/gic-pl390.c[pl390], which is a specific GIC model that predates the GICv2 spec I believe.
 
-TODO I hacked `#define GIC_GICC_BASE (GIC_BASE + 0xa0000)` and now continuing attempt.
+TODO if I hack `#define GIC_GICC_BASE (GIC_BASE + 0xa0000)`, then it goes a bit further, but the next loop never ends.
 
 ===== tukl-msd/gem5.bare-metal
 

baremetal/arch/aarch64/timer.c

@@ -4,48 +4,62 @@
 #include <lkmc.h>
 #include <lkmc/gicv3.h>
 
-#define CNTV_CTL_ENABLE  (1 << 0)
-#define CNTV_CTL_IMASK   (1 << 1)
-#define CNTV_CTL_ISTATUS (1 << 2)
-
-void cntv_ctl_el0_disable(void) {
-    lkmc_sysreg_cntv_ctl_el0_write(lkmc_sysreg_cntv_ctl_el0_read() & ~CNTV_CTL_ENABLE);
+void lkmc_vector_trap_handler(LkmcVectorExceptionFrame *exception __attribute__((unused))) {
+    printf("CNTVCT_EL0 0x%" PRIx64 "\n", lkmc_sysreg_cntvct_el0_read());
 }
 
-/* If enabled, when: cntv_ctl > cntv_cval then:
- *
- * * if CNTV_CTL_IMASK is clear, raise an interrupt
- * * set CNTV_CTL_ISTATUS
- */
-void cntv_ctl_el0_enable(void) {
+#define CNTV_CTL_ENABLE  (1 << 0) /* Enables the timer */ 
+#define CNTV_CTL_IMASK   (1 << 1) /* Timer interrupt mask bit */
+#define CNTV_CTL_ISTATUS (1 << 2) /* The status of the timer interrupt. This bit is read-only */
+
+/* DAIF, Interrupt Mask Bits */
+#define DAIF_DBG_BIT        (1<<3)  /* Debug mask bit */
+#define DAIF_ABT_BIT        (1<<2)  /* Asynchronous abort mask bit */
+#define DAIF_IRQ_BIT        (1<<1)  /* IRQ mask bit */
+#define DAIF_FIQ_BIT        (1<<0)  /* FIQ mask bit */
+
+#define wfi() __asm__ __volatile__ ("wfi" : : : "memory")
+
+void enable_cntv(void) {
     lkmc_sysreg_cntv_ctl_el0_write(lkmc_sysreg_cntv_ctl_el0_read() | CNTV_CTL_ENABLE);
 }
 
-
-void lkmc_vector_trap_handler(LkmcVectorExceptionFrame *exception __attribute__((unused))) {
+void enable_irq(void) {
+    __asm__ __volatile__ ("msr DAIFClr, %0" : : "i" (DAIF_IRQ_BIT)  : "memory");
 }
 
 int main(void) {
     /* Initial state. */
-    printf("cntv_ctl_el0 0x%" PRIx32 "\n", lkmc_sysreg_cntv_ctl_el0_read());
-    printf("cntfrq_el0 0x%" PRIx64 "\n", lkmc_sysreg_cntfrq_el0_read());
-    printf("cntv_cval_el0 0x%" PRIx64 "\n", lkmc_sysreg_cntv_cval_el0_read());
+    printf("CNTV_CTL_EL0 0x%" PRIx32 "\n", lkmc_sysreg_cntv_ctl_el0_read());
+    printf("CNTFRQ_EL0 0x%" PRIx64 "\n", lkmc_sysreg_cntfrq_el0_read());
+    printf("CNTV_CVAL_EL0 0x%" PRIx64 "\n", lkmc_sysreg_cntv_cval_el0_read());
 
     /* Get the counter value many times to watch the time pass. */
-    printf("cntvct_el0 0x%" PRIx64 "\n", lkmc_sysreg_cntvct_el0_read());
-    printf("cntvct_el0 0x%" PRIx64 "\n", lkmc_sysreg_cntvct_el0_read());
-    printf("cntvct_el0 0x%" PRIx64 "\n", lkmc_sysreg_cntvct_el0_read());
+    printf("CNTVCT_EL0 0x%" PRIx64 "\n", lkmc_sysreg_cntvct_el0_read());
+    printf("CNTVCT_EL0 0x%" PRIx64 "\n", lkmc_sysreg_cntvct_el0_read());
+    printf("CNTVCT_EL0 0x%" PRIx64 "\n", lkmc_sysreg_cntvct_el0_read());
 
-    /*gic_v3_initialize();*/
+    /**/
+    gic_v3_initialize();
     {
-        /*uint64_t ticks, current_cnt;*/
-        /*uint32_t cntfrq;*/
-        /*cntfrq = raw_read_cntfrq_el0();*/
-        /*ticks = cntfrq;*/
+        uint64_t ticks, current_cnt;
+        uint32_t cntfrq;
+        cntfrq = lkmc_sysreg_cntfrq_el0_read();
+        ticks = cntfrq;
+        current_cnt = lkmc_sysreg_cntvct_el0_read();
+        lkmc_sysreg_cntv_cval_el0_write(current_cnt + ticks);
+        enable_cntv();
+        enable_irq();
+    }
+    while (1) {
+        /*puts("qwer");*/
         /*current_cnt = raw_read_cntvct_el0();*/
-        /*raw_write_cntv_cval_el0(current_cnt + ticks);*/
-        /*enable_cntv();*/
-        /*enable_irq();*/
+        /*val = raw_read_cntv_ctl();*/
+        /*printf("CNTVCT_EL0 = ");*/
+        /*uart_puthex(current_cnt);*/
+        /*uart_puts(", CNTV_CTL_EL0 = ");*/
+        /*uart_puthex(val);*/
+        /*wfi();*/
     }
 
 #if 0

common.py

@@ -699,7 +699,7 @@ def join(*paths):
                         # http://lists.nongnu.org/archive/html/qemu-discuss/2018-08/msg00034.html
                         env['machine2'] = 'highmem=off'
                     elif env['arch'] == 'aarch64':
-                        env['machine2'] = 'gic_version=3'
+                        env['machine2'] = None
         else:
             env['machine2'] = None
 

lkmc/gicv3.h

@@ -7,7 +7,7 @@
 typedef int32_t irq_no;
 
 #define GIC_GICD_BASE (GIC_BASE)
-#define GIC_GICC_BASE (GIC_BASE + 0xa0000)
+#define GIC_GICC_BASE (GIC_BASE + 0x10000)
 
 #define GIC_GICD_INT_PER_REG            (32)
 #define GIC_GICD_IPRIORITY_PER_REG      (4)
@@ -135,9 +135,11 @@ static void init_gicc(void) {
     *REG_GIC_GICC_BPR = GICC_BPR_NO_GROUP;
 
     /* Clear all of the active interrupts */
-    for(pending_irq = ( *REG_GIC_GICC_IAR & GICC_IAR_INTR_IDMASK );
-        ( pending_irq != GICC_IAR_SPURIOUS_INTR );
-        pending_irq = ( *REG_GIC_GICC_IAR & GICC_IAR_INTR_IDMASK ) )
+    for (
+        pending_irq = (*REG_GIC_GICC_IAR & GICC_IAR_INTR_IDMASK);
+        pending_irq != GICC_IAR_SPURIOUS_INTR;
+        pending_irq = (*REG_GIC_GICC_IAR & GICC_IAR_INTR_IDMASK)
+    )
         *REG_GIC_GICC_EOIR = *REG_GIC_GICC_IAR;
 
     /* Enable CPU interface */
@@ -215,7 +217,6 @@ static int gicd_probe_pending(irq_no irq) {
 
     is_pending = ( *REG_GIC_GICD_ISPENDR( (irq / GIC_GICD_ISPENDR_PER_REG) ) &
         ( 1U << ( irq % GIC_GICD_ISPENDR_PER_REG ) ) );
-
     return ( is_pending != 0 );
 }
 
@@ -232,7 +233,6 @@ static void gicd_set_target(irq_no irq, uint32_t p){
     uint32_t    reg;
 
     shift = (irq % GIC_GICD_ITARGETSR_PER_REG) * GIC_GICD_ITARGETSR_SIZE_PER_REG;
-
     reg = *REG_GIC_GICD_ITARGETSR(irq / GIC_GICD_ITARGETSR_PER_REG);
     reg &= ~( ((uint32_t)(0xff)) << shift);
     reg |= (p << shift);

path_properties.py

@@ -303,6 +303,7 @@ def get(path):
                                 ),
                                 'return1.S': {'exit_status': 1},
                                 'semihost_exit.S': {'requires_semihosting': True},
+                                'timer.c': {'skip_run_unclassified': True},
                             },
                         )
                     }