Use level-triggered ISA interrupts.

2 files changed, 13 insertions, 0 deletions

diff --git a/init.c b/init.c
index 65a0909..76f2d59 100644
--- a/init.c
+++ b/init.c
@@ -234,6 +234,11 @@ init_pcb (void)
 static void
 init_i8259 (void)
 {
+  /* ??? MILO initializes the PIC as edge triggered; I do not know how SRM
+     initializes them.  However, Linux seems to expect that these are level
+     triggered.  That may be a kernel bug, but level triggers are more
+     reliable anyway so lets go with that.  */
+
   /* Initialize the slave PIC.  */
   outb(0x11, PORT_PIC2_CMD);	/* ICW1: edge trigger, cascade, ICW4 req */
   outb(0x08, PORT_PIC2_DATA);	/* ICW2: irq offset = 8 */
@@ -246,6 +251,12 @@ init_i8259 (void)
   outb(0x04, PORT_PIC1_DATA);	/* ICW3: slave control INTC2 */
   outb(0x01, PORT_PIC1_DATA);	/* ICW4 */
 
+  /* Initialize level triggers.  The CY82C693UB that's on real alpha
+     hardware doesn't have this; this is a PIIX extension.  However,
+     QEMU doesn't implement regular level triggers.  */
+  outb(0xff, PORT_PIC2_ELCR);
+  outb(0xff, PORT_PIC1_ELCR);
+
   /* Disable all interrupts.  */
   outb(0xff, PORT_PIC2_DATA);
   outb(0xff, PORT_PIC1_DATA);
diff --git a/ioport.h b/ioport.h
index 0876c2a..b1bb4b3 100644
--- a/ioport.h
+++ b/ioport.h
@@ -53,6 +53,8 @@
 #define PORT_HD_DATA           0x03f6
 #define PORT_FD_DIR            0x03f7
 #define PORT_SERIAL1           0x03f8
+#define PORT_PIC1_ELCR         0x04d0
+#define PORT_PIC2_ELCR         0x04d1
 #define PORT_PCI_CMD           0x0cf8
 #define PORT_PCI_REBOOT        0x0cf9
 #define PORT_PCI_DATA          0x0cfc