kernel/arch/i386/platform/misc/pit.c

   1 #include <core/system.h>
   2 #include <core/string.h>
   3 #include <core/kargs.h>
   4 #include <cpu/io.h>
   5 #include <platform/misc.h>
   6
   7 static struct ioaddr pit_ioaddr;
   8
   9 #define PIT_CHANNEL0    0x00
  10 #define PIT_CMD         0x03
  11
  12 struct pit_cmd_register {
  13     union {
  14         struct {
  15             uint32_t bcd    : 1;
  16             uint32_t mode   : 3;
  17             uint32_t access : 2;
  18             uint32_t channel: 2;
  19         } __packed;
  20         uint8_t raw;
  21     } __packed;
  22 } __packed;
  23
  24 #define PIT_MODE_RATE_GENERATOR 0x2
  25 #define PIT_MODE_SQUARE_WAVE    0x3
  26 #define PIT_ACCESS_LOHIBYTE     0x3
  27
  28 int x86_pit_setup(struct ioaddr *io)
  29 {
  30     printk("i8254: Initializing [%p (%s)]\n", io->addr, ioaddr_type_str(io));
  31     pit_ioaddr = *io;
  32     return 0;
  33 }
  34
  35 #define FBASE   1193182ULL  /* PIT Oscillator operates at 1.193182 MHz */
  36
  37 static uint32_t atou32(const char *s)
  38 {
  39     uint32_t ret = 0;
  40
  41     while (*s) {
  42         ret = ret * 10 + (*s - '0');
  43         ++s;
  44     }
  45
  46     return ret;
  47 }
  48
  49 uint32_t x86_pit_period_set(uint32_t period_ns)
  50 {
  51     printk("i8254: requested period %d ns\n", period_ns);
  52
  53     uint32_t div;
  54     const char *arg_div = NULL;
  55
  56     if (!kargs_get("i8254.div", &arg_div)) {
  57         div = atou32(arg_div);
  58     } else {
  59         div = period_ns/838UL;
  60     }
  61
  62     if (div == 0) div = 1;
  63
  64     period_ns = 1000000000UL/(FBASE/div);
  65
  66     printk("i8254: Setting period to %d ns (div = %d)\n", period_ns, div);
  67
  68     struct pit_cmd_register cmd = {
  69         .bcd = 0,
  70         .mode = PIT_MODE_SQUARE_WAVE,
  71         .access = PIT_ACCESS_LOHIBYTE,
  72         .channel = 0,
  73     };
  74
  75     io_out8(&pit_ioaddr, PIT_CMD, cmd.raw);
  76     io_out8(&pit_ioaddr, PIT_CHANNEL0, (div >> 0) & 0xFF);
  77     io_out8(&pit_ioaddr, PIT_CHANNEL0, (div >> 8) & 0xFF);
  78
  79     return period_ns;
  80 }