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