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Diffstat (limited to 'include/x86/pit.h')
| -rw-r--r-- | include/x86/pit.h | 82 |
1 files changed, 82 insertions, 0 deletions
diff --git a/include/x86/pit.h b/include/x86/pit.h new file mode 100644 index 0000000..269fcec --- /dev/null +++ b/include/x86/pit.h @@ -0,0 +1,82 @@ +/* +** @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 |