From 247b2302128a0d02ba9f2c8683c62d4ac70cb22a Mon Sep 17 00:00:00 2001
From: d00f <8052722+DrDoof@users.noreply.github.com>
Date: Tue, 8 Sep 2026 23:35:27 +0200
Subject: [PATCH] Do not enter Idle mode from the external interrupt 2 handler

isr_ext2() ends with PCON |= 1, putting the core to sleep from inside an
interrupt handler.

The DW8051 leaves idle when any enabled interrupt is activated, so the core
does not stay down for long. It naps until the next enabled interrupt request
turns up, with the 200 Hz system tick putting a ceiling of 5 ms on that, and
then carries on.

The sleep buys nothing either way, because the instruction after it is the
return. While it lasts the handler holds the priority latch, so everything at
its level or below waits, and that includes the tick, the console and the NIC
receive interrupt.

The handler still clears its flag, which is what it has to do. The bit numbers
beside the two masks were wrong: 0xef clears bit 4 and 0xdf clears bit 5,
not 7 and 6.
---
 rtlplayground.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/rtlplayground.c b/rtlplayground.c
index f129a64b..bbca65b3 100644
--- a/rtlplayground.c
+++ b/rtlplayground.c
@@ -515,7 +515,7 @@ void isr_ext1(void) __interrupt(2)
  */
 void isr_ext2(void) __interrupt(8)
 {
-	EXIF &= 0xef;
+	EXIF &= 0xef;	// Clear IRQ flag (bit 4) in EXIF
 }
 
 /*
@@ -524,7 +524,7 @@ void isr_ext2(void) __interrupt(8)
  */
 void isr_ext3(void) __interrupt(9)
 {
-	EXIF &= 0xdf;
+	EXIF &= 0xdf;	// Clear IRQ flag (bit 5) in EXIF
 }
 
 // Timer2: handles system tick.