Added low power mode, for chips which need to start with clkdiv8 and only switch to 16.5mhz when usb connection is detected somehow.

2 files changed, 44 insertions, 3 deletions

diff --git a/firmware/bootloaderconfig.h b/firmware/bootloaderconfig.h
index 9869b72..b443d6e 100644
--- a/firmware/bootloaderconfig.h
+++ b/firmware/bootloaderconfig.h
@@ -16,7 +16,6 @@
 #define BOOTLOADER_ADDRESS 0
 #endif
 
-
 /*
 General Description:
 This file (together with some settings in Makefile) configures the boot loader
@@ -207,9 +206,22 @@ these macros are defined, the boot loader uses them.
 #define AUTO_EXIT_MS    2500
 //#define AUTO_EXIT_CONDITION()   (idlePolls > (AUTO_EXIT_MS * 10UL))
 
+// uncomment for chips with clkdiv8 enabled in fuses
+//#define LOW_POWER_MODE 1
+// restore cpu speed calibration back to 8/16mhz instead of 8.25/16.5mhz
+//#define RESTORE_OSCCAL 1
+// set clock prescaler to a value before running user program
+//#define SET_CLOCK_PRESCALER _BV(CLKPS0) /* divide by 2 for 8mhz */
 
 #define bootLoaderCondition()   (idlePolls < (AUTO_EXIT_MS * 10UL))
-
+#if LOW_POWER_MODE
+  // only starts bootloader if USB D- is pulled high on startup - by putting your pullup in to an external connector
+  // you can avoid ever entering an out of spec clock speed or waiting on bootloader when that pullup isn't there
+  #define bootLoaderStartCondition() \
+    (PINB & (_BV(USB_CFG_DMINUS_BIT) | _BV(USB_CFG_DMINUS_BIT))) == _BV(USB_CFG_DMINUS_BIT)
+#else
+  #define bootLoaderStartCondition() 1
+#endif
 
 /* ----------------------- Optional MCU Description ------------------------ */
 
diff --git a/firmware/main.c b/firmware/main.c
index 08ec1db..62097b8 100644
--- a/firmware/main.c
+++ b/firmware/main.c
@@ -375,12 +375,26 @@ static inline void leaveBootloader(void) {
 
 int __attribute__((noreturn)) main(void) {
     /* initialize  */
+    #ifdef RESTORE_OSCCAL
+        uint8_t osccal_default = OSCCAL;
+    #endif
+    #if (!SET_CLOCK_PRESCALER) && LOW_POWER_MODE
+        uint8_t prescaler_default = CLKPR;
+    #endif
+    
     wdt_disable();      /* main app may have enabled watchdog */
     tiny85FlashInit();
     bootLoaderInit();
     
     
-    if (bootLoaderCondition()) {
+    if (bootLoaderStartCondition()) {
+        #if LOW_POWER_MODE
+            // turn off clock prescalling - chip must run at full speed for usb
+            // if you might run chip at lower voltages, detect that in bootLoaderStartCondition
+            CLKPR = 1 << CLKPCE;
+            CLKPR = 0;
+        #endif
+        
         initForUsbConnectivity();
         do {
             usbPoll();
@@ -404,6 +418,21 @@ int __attribute__((noreturn)) main(void) {
         } while(bootLoaderCondition());  /* main event loop runs so long as bootLoaderCondition remains truthy */
     }
     
+    // set clock prescaler to desired clock speed (changing from clkdiv8, or no division, depending on fuses)
+    #if LOW_POWER_MODE
+        #ifdef SET_CLOCK_PRESCALER
+            CLKPR = 1 << CLKPCE;
+            CLKPR = SET_CLOCK_PRESCALER;
+        #else
+            CLKPR = 1 << CLKPCE;
+            CLKPR = prescaler_default;
+        #endif
+    #endif
+    
+    // slowly bring down OSCCAL to it's original value before launching in to user program
+    #ifdef RESTORE_OSCCAL
+        while (OSCCAL > osccal_default) { OSCCAL -= 1; }
+    #endif
     leaveBootloader();
 }