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boards/common/atmega: gracefully handle CKDIV8 fuse #8952

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merged 1 commit into from
May 14, 2018
Merged

boards/common/atmega: gracefully handle CKDIV8 fuse #8952

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5 changes: 5 additions & 0 deletions boards/common/atmega/board.c
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Original file line number Diff line number Diff line change
Expand Up @@ -23,10 +23,15 @@
#include "irq.h"
#include "periph/gpio.h"

#ifndef CPU_ATMEGA_CLK_SCALE_INIT
#define CPU_ATMEGA_CLK_SCALE_INIT CPU_ATMEGA_CLK_SCALE_DIV1
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This should go into ./boards/common/arduino-atmega/include/periph_conf.h preferably under the CLOCK_CORECLOCK definition and with a small bit of doxygen.

Can be done without the #ifndef construction but I don't mind keeping it.

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Problem though: not all boards using boards/common/atmega are Arduinos.

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I think we can solve that problem in a follow up PR. Discussed a bit offline with @bergzand and maybe found a solution.

#endif

void led_init(void);

void board_init(void)
{
atmega_set_prescaler(CPU_ATMEGA_CLK_SCALE_INIT);
atmega_stdio_init();
cpu_init();
led_init();
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31 changes: 31 additions & 0 deletions cpu/atmega_common/include/cpu.h
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Expand Up @@ -92,6 +92,37 @@ __attribute__((always_inline)) static inline void cpu_print_last_instruction(voi
printf("Stack Pointer: 0x%04x\n", ptr);
}

/**
* @brief ATmega system clock prescaler settings
*
* Some CPUs may not support the highest prescaler settings
*/
enum {
CPU_ATMEGA_CLK_SCALE_DIV1 = 0,
CPU_ATMEGA_CLK_SCALE_DIV2 = 1,
CPU_ATMEGA_CLK_SCALE_DIV4 = 2,
CPU_ATMEGA_CLK_SCALE_DIV8 = 3,
CPU_ATMEGA_CLK_SCALE_DIV16 = 4,
CPU_ATMEGA_CLK_SCALE_DIV32 = 5,
CPU_ATMEGA_CLK_SCALE_DIV64 = 6,
CPU_ATMEGA_CLK_SCALE_DIV128 = 7,
CPU_ATMEGA_CLK_SCALE_DIV256 = 8,
CPU_ATMEGA_CLK_SCALE_DIV512 = 9,
};

/**
* @brief Initializes system clock prescaler
*/
static inline void atmega_set_prescaler(uint8_t clk_scale)
{
/* Enable clock change */
/* Must be assignment to set all other bits to zero, see datasheet */
CLKPR = (1 << CLKPCE);

/* Write clock within 4 cycles */
CLKPR = clk_scale;
}

/**
* @brief Initializes avrlibc stdio
*/
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