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/*
** @file pit.h
**
** @author Warren R. Carithers
** @author K. Reek
**
** Definitions of constants and macros for the
** Intel 8254 Programmable Interval Timer
**
*/
#ifndef X86PIT_H_
#define X86PIT_H_
/*
** Hardware timer (Intel 8254 Programmable Interval Timer)
**
** Control word layout:
**
** Bit 7 6 | 5 4 | 3 2 1 | 0
** Field SC1 SC0|RW1 RW0|M2 M1 M0 |BCD
**
** SC - select counter
** RW - read/write
** M - mode
** BCD - binary or BCD counter
*/
/* Frequency settings */
#define PIT_DEFAULT_TICKS_PER_SECOND 18 // actually 18.2065Hz
#define PIT_DEFAULT_MS_PER_TICK (1000/PIT_DEFAULT_TICKS_PER_SECOND)
#define PIT_FREQ 1193182 // clock cycles/sec
/* Port assignments */
#define PIT_BASE_PORT 0x40 // I/O port for the timer
# define PIT_0_PORT (PIT_BASE_PORT)
# define PIT_1_PORT (PIT_BASE_PORT+1)
# define PIT_2_PORT (PIT_BASE_PORT+2)
# define PIT_CONTROL_PORT (PIT_BASE_PORT+3)
/* BCD field */
#define PIT_USE_DECIMAL 0x00 // 16-bit binary counter (default)
#define PIT_USE_BCD 0x01 // BCD counter
/* Timer modes */
#define PIT_MODE_0 0x00 // int on terminal count
#define PIT_MODE_1 0x02 // one-shot
#define PIT_MODE_2 0x04 // divide-by-N
#define PIT_MODE_3 0x06 // square-wave
#define PIT_MODE_4 0x08 // software strobe
#define PIT_MODE_5 0x0a // hardware strobe
/* Timer 0 settings */
#define PIT_0_SELECT 0x00 // select timer 0
#define PIT_0_LOAD 0x30 // load LSB, then MSB
#define PIT_0_NDIV PIT_MODE_2 // divide-by-N counter
#define PIT_0_SQUARE PIT_MODE_3 // square-wave mode
#define PIT_0_ENDSIGNAL 0x00 // assert OUT at end of count
/* Timer 1 settings */
#define PIT_1_SELECT 0x40 // select timer 1
#define PIT_1_READ 0x30 // read/load LSB then MSB
#define PIT_1_RATE 0x06 // square-wave, for USART
/* Timer 2 settings */
#define PIT_2_SELECT 0x80 // select timer 1
#define PIT_2_READ 0x30 // read/load LSB then MSB
#define PIT_2_RATE 0x06 // square-wave, for USART
/* Timer read-back */
#define PIT_READBACK 0xc0 // perform a read-back
#define PIT_RB_NOT_COUNT 0x20 // don't latch the count
#define PIT_RB_NOT_STATUS 0x10 // don't latch the status
#define PIT_RB_CHAN_2 0x08 // read back channel 2
#define PIT_RB_CHAN_1 0x04 // read back channel 1
#define PIT_RB_CHAN_0 0x02 // read back channel 0
#define PIT_RB_ACCESS_MASK 0x30 // access mode field
#define PIT_RB_OP_MASK 0x0e // oper mode field
#define PIT_RB_BCD_MASK 0x01 // BCD mode field
#endif
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