Change GIC example to handle nested interrupts.

It can now handle a hi-prio SGI whilst in the middle of handling a low-prio SGI. This shows we got the asm interrupt handler's stacking code right (probably).

Author: thejpster

examples/mps3-an536/src/bin/gic.rs

@@ -23,6 +23,9 @@ const GICD_BASE_OFFSET: usize = 0x0000_0000usize;
 /// Offset from PERIPHBASE for the first GIC Redistributor
 const GICR_BASE_OFFSET: usize = 0x0010_0000usize;
 
+const SGI_INTID_LO: IntId = IntId::sgi(3);
+const SGI_INTID_HI: IntId = IntId::sgi(4);
+
 /// The entry-point to the Rust application.
 ///
 /// It is called by the start-up code in `cortex-r-rt`.
@@ -46,13 +49,17 @@ fn main() -> ! {
     SingleCoreGic::set_priority_mask(0x80);
 
     // Configure a Software Generated Interrupt for Core 0
-    println!("Configure SGI...");
-    let sgi_intid = IntId::sgi(3);
-    gic.set_interrupt_priority(sgi_intid, Some(0), 0x31);
-    gic.set_group(sgi_intid, Some(0), Group::Group1NS);
+    println!("Configure low-prio SGI...");
+    gic.set_interrupt_priority(SGI_INTID_LO, Some(0), 0x31);
+    gic.set_group(SGI_INTID_LO, Some(0), Group::Group1NS);
+
+    println!("Configure high-prio SGI...");
+    gic.set_interrupt_priority(SGI_INTID_HI, Some(0), 0x10);
+    gic.set_group(SGI_INTID_HI, Some(0), Group::Group1NS);
 
     println!("gic.enable_interrupt()");
-    gic.enable_interrupt(sgi_intid, Some(0), true);
+    gic.enable_interrupt(SGI_INTID_LO, Some(0), true);
+    gic.enable_interrupt(SGI_INTID_HI, Some(0), true);
 
     println!("Enabling interrupts...");
     dump_cpsr();
@@ -62,9 +69,9 @@ fn main() -> ! {
     dump_cpsr();
 
     // Send it
-    println!("Send SGI");
+    println!("Send lo-prio SGI");
     SingleCoreGic::send_sgi(
-        sgi_intid,
+        SGI_INTID_LO,
         SgiTarget::List {
             affinity3: 0,
             affinity2: 0,
@@ -89,7 +96,29 @@ fn dump_cpsr() {
 fn irq_handler() {
     println!("> IRQ");
     while let Some(int_id) = SingleCoreGic::get_and_acknowledge_interrupt() {
-        println!("- IRQ handle {:?}", int_id);
+        // let's go re-entrant
+        unsafe {
+            cortex_ar::interrupt::enable();
+        }
+        println!("- IRQ Handing {:?}", int_id);
+        if int_id == SGI_INTID_LO {
+            println!(
+                "- IRQ got {:?}, sending hi-prio {:?}",
+                SGI_INTID_LO, SGI_INTID_HI
+            );
+            SingleCoreGic::send_sgi(
+                SGI_INTID_HI,
+                SgiTarget::List {
+                    affinity3: 0,
+                    affinity2: 0,
+                    affinity1: 0,
+                    target_list: 0b1,
+                },
+            );
+            println!("- IRQ finished sending hi-prio!");
+        }
+        // turn interrupts off again
+        cortex_ar::interrupt::disable();
         SingleCoreGic::end_interrupt(int_id);
     }
     println!("< IRQ");