From c486e1f01ec128d9c485e546ccec0d7d856ce45b Mon Sep 17 00:00:00 2001
From: Mike Naberezny <mike@naberezny.com>
Date: Tue, 21 Nov 2023 13:24:47 -0800
Subject: [PATCH] Drop down to 1 MHz to save a little power

---
 firmware/fuses.asm |  2 +-
 firmware/main.asm  | 28 +++++++++++++++++++++++-----
 2 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/firmware/fuses.asm b/firmware/fuses.asm
index 6a41566..dac8ac6 100644
--- a/firmware/fuses.asm
+++ b/firmware/fuses.asm
@@ -13,7 +13,7 @@
 
 ;Oscillator Configuration
 .org 0+FUSE_OSCCFG_offset
-.byte (0<<FUSE_OSCLOCK_bp) | FUSE_FREQSEL_20MHZ_gc
+.byte (0<<FUSE_OSCLOCK_bp) | FUSE_FREQSEL_16MHZ_gc
 
 ;Reserved fuse between OSCCFG and TCD0CFG should not be programmed
 
diff --git a/firmware/main.asm b/firmware/main.asm
index ab3653a..b1ea5d0 100644
--- a/firmware/main.asm
+++ b/firmware/main.asm
@@ -49,6 +49,13 @@ LOCK0 = 0
     .assume . - ((PROGMEM_START/2) + INT_VECTORS_SIZE)
 
 reset:
+    ;Set main clock to 16 MHz to get through init quickly
+    ;in case the computer checks for a key at boot.
+    ldi r16, CPU_CCP_IOREG_gc
+    clr r17                             ;No prescaler = 16 MHz
+    out CPU_CCP, r16                    ;Unlock Protected I/O Registers
+    sts CLKCTRL_MCLKCTRLB, r17          ;Disable main clock prescaler
+
     ;Clear RAM
     ldi ZL, <INTERNAL_SRAM_START
     ldi ZH, >INTERNAL_SRAM_START
@@ -75,7 +82,15 @@ reset:
     rcall eeprom_read_contacts  ;Read 4066 contacts saved in EEPROM
     rcall gpio_write_contacts   ;  and restore the 4066 to that state
 
-    ldi r16, 0                  ;Initialize variables to defaults
+    ;Now that the 4066 is set up, drop down to 1 MHz.  The clock
+    ;will run at 1 MHz from now on to save a little power.
+    ldi r16, CPU_CCP_IOREG_gc
+    ldi r17, 0x03<<1 | CLKCTRL_PEN_bm   ;Prescaler for 1 MHz
+    out CPU_CCP, r16                    ;Unlock Protected I/O Registers
+    sts CLKCTRL_MCLKCTRLB, r17          ;Set main clock prescaler
+
+    ;Initialize variables to defaults
+    clr r16
     sts current_keys, r16
     sts previous_keys, r16
     sts lock0_down_ticks, r16
@@ -107,7 +122,7 @@ main_loop:
 ;Check each key and toggle its 4066 contact if it was just pushed down.
 ;
 task_keys:
-    ldi r18, 1<<LOCK3       ;First key to check (highest bit position)
+    ldi r18, 1<<LOCK3           ;First key to check (highest bit position)
 
 1$: lds r16, current_keys
     and r16, r18                ;Leave only key of interest from current
@@ -237,16 +252,19 @@ wait_n_ms:
     ret
 
 ;Busy wait for 1 millisecond
+;Assumes 1 MHz clock
 ;
 wait_1_ms:
     push r16
     push r17
-    ldi r16, 0x05
-1$: ldi r17, 0xde
+
+    ldi r16, 0x02
+1$: ldi r17, 0xa6
 2$: dec r17
     brne 2$
     dec r16
     brne 1$
+
     pop r17
     pop r16
     ret
@@ -488,7 +506,7 @@ eeprom_read_contacts:
     brne 1$
     cpi YH, #>EEPROM_START
     brne 1$
-    ldi r16, 0                          ;EEPROM is empty; return 0 (all off)
+    clr r16                             ;EEPROM is empty; return 0 (all off)
 2$: ret
 
 ;Store R16 as the 4066 contact state in the EEPROM