From 84a11e746f5a445e80eb9b6a21c9768a9e06bc6c Mon Sep 17 00:00:00 2001
From: Jeremy Soller <jeremy@system76.com>
Date: Thu, 5 Nov 2020 12:49:07 -0700
Subject: [PATCH] Reduce AVR clock to 8MHz

---
 keyboards/system76/launch_beta_1/rules.mk | 6 ++++--
 tmk_core/protocol/lufa/lufa.c             | 6 ++++++
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/keyboards/system76/launch_beta_1/rules.mk b/keyboards/system76/launch_beta_1/rules.mk
index bc8d6fe734a..85774a90d48 100644
--- a/keyboards/system76/launch_beta_1/rules.mk
+++ b/keyboards/system76/launch_beta_1/rules.mk
@@ -4,8 +4,10 @@ MCU = atmega32u4
 # Allow flashing with usbasp
 AVRDUDE_MCU = $(MCU)
 
-# Processor frequency
-F_CPU = 16000000
+# CPU frequency divided by two since AVR is at 3.3V
+F_CPU = 8000000
+# External oscillator is 16Mhz
+F_USB = 16000000
 
 # Bootloader selection
 #   Teensy       halfkay
diff --git a/tmk_core/protocol/lufa/lufa.c b/tmk_core/protocol/lufa/lufa.c
index 8319b34e94d..46a65c27aae 100644
--- a/tmk_core/protocol/lufa/lufa.c
+++ b/tmk_core/protocol/lufa/lufa.c
@@ -917,8 +917,14 @@ static void setup_mcu(void) {
     MCUSR &= ~_BV(WDRF);
     wdt_disable();
 
+// HACK for System76 boards with AVR at 3.3V and crystal at 16 MHz
+#if (F_CPU == 8000000 && F_USB == 16000000)
+    /* Divide clock by 2 */
+    clock_prescale_set(clock_div_2);
+#else
     /* Disable clock division */
     clock_prescale_set(clock_div_1);
+#endif
 }
 
 /** \brief Setup USB