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avr: Add config option to clear the CPU prescaler 

Some AVR chips ship with a 1/8th clock divisor set.  Add a compile
time option to manually clear this field at startup.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2016-06-05 10:29:09 -04:00
parent 38f1d78e1b
commit 91e7807af6
2 changed files with 23 additions and 0 deletions
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14
src/avr/Kconfig
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@ -44,6 +44,20 @@ config CLOCK_FREQ
default 16000000 if AVR_FREQ_16000000 default 16000000 if AVR_FREQ_16000000
default 20000000 if AVR_FREQ_20000000 default 20000000 if AVR_FREQ_20000000
config CLEAR_PRESCALER
bool "Manually clear the CPU prescaler field at startup"
default n
help
Some AVR chips ship with a "clock prescaler" that causes the
chip to run at 1/8th speed. Enable this setting to clear the
prescaler field at startup which will cause the chip to run
without a clock divisor.
config AVR_CLKPR
int
default 0 if CLEAR_PRESCALER
default -1
config AVR_STACK_SIZE config AVR_STACK_SIZE
int int
default 256 if MACH_atmega2560 default 256 if MACH_atmega2560

9
src/avr/timer.c
View File

@ -5,6 +5,7 @@
// This file may be distributed under the terms of the GNU GPLv3 license. // This file may be distributed under the terms of the GNU GPLv3 license.
#include <avr/interrupt.h> // TCNT1 #include <avr/interrupt.h> // TCNT1
#include "autoconf.h" // CONFIG_AVR_CLKPR
#include "command.h" // shutdown #include "command.h" // shutdown
#include "irq.h" // irq_save #include "irq.h" // irq_save
#include "sched.h" // sched_timer_kick #include "sched.h" // sched_timer_kick
@ -49,6 +50,14 @@ ISR(TIMER1_COMPA_vect)
static void static void
timer_init(void) timer_init(void)
{ {
if (CONFIG_AVR_CLKPR != -1 && (uint8_t)CONFIG_AVR_CLKPR != CLKPR) {
// Program the clock prescaler
uint8_t flag = irq_save();
CLKPR = 0x80;
CLKPR = CONFIG_AVR_CLKPR;
irq_restore(flag);
}
// no outputs // no outputs
TCCR1A = 0; TCCR1A = 0;
// Normal Mode // Normal Mode