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Diffstat (limited to 'firmware/osccal.h')
| -rw-r--r-- | firmware/osccal.h | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/firmware/osccal.h b/firmware/osccal.h new file mode 100644 index 0000000..af37a43 --- /dev/null +++ b/firmware/osccal.h @@ -0,0 +1,57 @@ +/* Name: osccal.h + * Author: Christian Starkjohann + * Creation Date: 2008-04-10 + * Changes 2013-11-04 cpldcpu@gmail.com + * Tabsize: 4 + * Copyright: (c) 2008 by OBJECTIVE DEVELOPMENT Software GmbH + * License: GNU GPL v2 (see License.txt), GNU GPL v3 or proprietary (CommercialLicense.txt) + */ + +/* +General Description: +This module contains a function which calibrates the AVR's internal RC +oscillator so that the CPU runs at F_CPU (F_CPU is a macro which must be +defined when the module is compiled, best passed in the compiler command +line). The time reference is the USB frame clock of 1 kHz available +immediately after a USB RESET condition. Timing is done by counting CPU +cycles, so all interrupts must be disabled while the calibration runs. +The size optimized assembler implementation includes its own implementation +of usbMeasureFrameLength. Therefore USB_CFG_HAVE_MEASURE_FRAME_LENGTH should +be set to 0 to avoid including unused code sections. It is recommended to call +calibrateOscillatorASM() from the reset hook in usbconfig.h by including osccal.h: + +#include "osccal.h" + +This routine is an alternative to the continuous synchronization described +in osctune.h. + +Algorithm used: See osccalASM.x + +Limitations: +This calibration algorithm may try OSCCAL values of up to 192 even if the +optimum value is far below 192. It may therefore exceed the allowed clock +frequency of the CPU in low voltage designs! +Precision depends on the OSCCAL vs. frequency dependency of the oscillator. +Typical precision for an ATMega168 (derived from the OSCCAL vs. F_RC diagram +in the data sheet) should be in the range of 0.4%. Only the 12.8 MHz and +16.5 MHz versions of V-USB (with built-in receiver PLL) can tolerate this +deviation! All other frequency modules require at least 0.2% precision. +*/ + +#ifndef __OSCCAL_H_INCLUDED__ +#define __OSCCAL_H_INCLUDED__ + +#ifndef __ASSEMBLER__ + void calibrateOscillatorASM(void); +# define USB_RESET_HOOK(resetStarts) if(!resetStarts){ calibrateOscillatorASM();} +# define USB_CFG_HAVE_MEASURE_FRAME_LENGTH 0 +#endif +/* This function calibrates the RC oscillator so that the CPU runs at F_CPU. + * It MUST be called immediately after the end of a USB RESET condition! + * Disable all interrupts during the call! + * It is recommended that you store the resulting value in EEPROM so that a + * good guess value is available after the next reset. + */ + + +#endif /* __OSCCAL_H_INCLUDED__ */ |