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static void spd_enable_refresh(void)
{
/*
* Effects: Uses serial presence detect to set the
* refresh rate in the DRAMC register.
* see spd_set_dramc for the other values.
* FIXME: Check for illegal/unsupported ram configurations and abort
*/
static const unsigned char refresh_rates[] = {
0x01, /* Normal 15.625 us -> 15.6 us */
0x05, /* Reduced(.25X) 3.9 us -> 7.8 us */
0x05, /* Reduced(.5X) 7.8 us -> 7.8 us */
0x02, /* Extended(2x) 31.3 us -> 31.2 us */
0x03, /* Extended(4x) 62.5 us -> 62.4 us */
0x04, /* Extended(8x) 125 us -> 124.8 us */
};
/* Find the first dimm and assume the rest are the same */
int byte;
unsigned device;
unsigned refresh_rate;
byte = -1;
device = 0x50;
while ((byte < 0) && (device <= 0x57)) {
byte = __builtin_inl(device);
device += 1;
}
if (byte < 0) {
/* We couldn't find anything we must have no memory */
while(1);
}
byte &= 0x7f;
/* Default refresh rate be conservative */
refresh_rate = 5;
/* see if the ram refresh is a supported one */
if (byte < 6) {
refresh_rate = refresh_rates[byte];
}
byte = __builtin_inb(0x57);
byte &= 0xf8;
byte |= refresh_rate;
__builtin_outb(byte, 0x57);
}
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