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nuclear@33
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1 #include <stdio.h>
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nuclear@33
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2 #include "intr.h"
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nuclear@33
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3 #include "asmops.h"
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nuclear@33
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4 #include "config.h"
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5
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nuclear@33
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6 /* frequency of the oscillator driving the 8254 timer */
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nuclear@33
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7 #define OSC_FREQ_HZ 1193182
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8
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nuclear@33
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9 /* macro to divide and round to the nearest integer */
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nuclear@33
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10 #define DIV_ROUND(a, b) ((a) / (b) + ((a) % (b)) / ((b) / 2))
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11
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nuclear@33
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12 /* I/O ports connected to the 8254 */
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nuclear@33
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13 #define PORT_DATA0 0x40
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nuclear@33
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14 #define PORT_DATA1 0x41
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nuclear@33
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15 #define PORT_DATA2 0x42
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nuclear@33
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16 #define PORT_CMD 0x43
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17
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nuclear@33
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18 /* command bits */
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nuclear@33
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19 #define CMD_CHAN0 0
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nuclear@33
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20 #define CMD_CHAN1 (1 << 6)
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nuclear@33
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21 #define CMD_CHAN2 (2 << 6)
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nuclear@33
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22 #define CMD_RDBACK (3 << 6)
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23
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nuclear@33
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24 #define CMD_LATCH 0
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nuclear@33
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25 #define CMD_ACCESS_LOW (1 << 4)
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nuclear@33
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26 #define CMD_ACCESS_HIGH (2 << 4)
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nuclear@33
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27 #define CMD_ACCESS_BOTH (3 << 4)
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28
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nuclear@33
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29 #define CMD_OP_INT_TERM 0
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nuclear@33
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30 #define CMD_OP_ONESHOT (1 << 1)
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nuclear@33
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31 #define CMD_OP_RATE (2 << 1)
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nuclear@33
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32 #define CMD_OP_SQWAVE (3 << 1)
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nuclear@33
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33 #define CMD_OP_SOFT_STROBE (4 << 1)
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nuclear@33
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34 #define CMD_OP_HW_STROBE (5 << 1)
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35
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nuclear@33
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36 #define CMD_MODE_BIN 0
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nuclear@33
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37 #define CMD_MODE_BCD 1
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38
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39
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nuclear@33
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40 static void intr_handler();
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41
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nuclear@33
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42 static unsigned long nticks;
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43
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44
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nuclear@33
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45 void init_timer(void)
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46 {
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nuclear@33
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47 /* calculate the reset count: round(osc / freq) */
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nuclear@33
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48 int reset_count = DIV_ROUND(OSC_FREQ_HZ, TICK_FREQ_HZ);
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49
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nuclear@33
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50 /* set the mode to square wave for channel 0, both low
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51 * and high reset count bytes will follow...
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52 */
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nuclear@33
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53 outb(CMD_CHAN0 | CMD_ACCESS_BOTH | CMD_OP_SQWAVE, PORT_CMD);
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54
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55 /* write the low and high bytes of the reset count to the
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56 * port for channel 0
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57 */
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58 outb(reset_count & 0xff, PORT_DATA0);
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nuclear@33
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59 outb((reset_count >> 8) & 0xff, PORT_DATA0);
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60
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61 nticks = 0;
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62
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nuclear@33
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63 /* set the timer interrupt handler */
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64 interrupt(32, intr_handler);
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nuclear@33
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65 }
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66
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nuclear@33
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67 /* This will be called by the interrupt dispatcher approximately
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68 * every 1/250th of a second, so it must be extremely fast.
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69 * For now, just increasing a tick counter will suffice.
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70 */
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71 static void intr_handler()
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72 {
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73 nticks++;
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74
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75 if(nticks % TICK_FREQ_HZ == 0) {
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76 printf("%lu sec\n", nticks / TICK_FREQ_HZ);
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77 }
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78 }
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