85 lines
1.8 KiB
C
85 lines
1.8 KiB
C
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#include <pc80/mc146818rtc.h>
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#include <part/fallback_boot.h>
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static unsigned char cmos_read(unsigned char addr)
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{
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outb(addr, RTC_BASE_PORT + 0);
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return inb(RTC_BASE_PORT + 1);
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}
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static void cmos_write(unsigned char val, unsigned char addr)
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{
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outb(addr, RTC_BASE_PORT + 0);
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outb(val, RTC_BASE_PORT + 1);
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}
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static int cmos_error(void)
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{
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unsigned char reg_d;
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/* See if the cmos error condition has been flagged */
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reg_d = cmos_read(RTC_REG_D);
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return (reg_d & RTC_VRT) == 0;
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}
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static int cmos_chksum_valid(void)
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{
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unsigned char addr;
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unsigned long sum, old_sum;
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sum = 0;
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/* Comput the cmos checksum */
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for(addr = LB_CKS_RANGE_START; addr <= LB_CKS_RANGE_END; addr++) {
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sum += cmos_read(addr);
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}
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sum = (sum & 0xffff) ^ 0xffff;
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/* Read the stored checksum */
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old_sum = cmos_read(LB_CKS_LOC) << 8;
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old_sum |= cmos_read(LB_CKS_LOC+1);
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return sum == old_sum;
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}
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static int do_normal_boot(void)
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{
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unsigned char byte;
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if (cmos_error() || !cmos_chksum_valid()) {
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unsigned char byte;
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/* There are no impossible values, no cheksums so just
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* trust whatever value we have in the the cmos,
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* but clear the fallback bit.
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*/
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byte = cmos_read(RTC_BOOT_BYTE);
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byte &= 0x0c;
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byte |= MAX_REBOOT_CNT << 4;
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cmos_write(byte, RTC_BOOT_BYTE);
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}
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/* The RTC_BOOT_BYTE is now o.k. see where to go. */
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byte = cmos_read(RTC_BOOT_BYTE);
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/* Are we in normal mode? */
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if (byte & 1) {
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byte &= 0x0f; /* yes, clear the boot count */
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}
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/* Are we already at the max count? */
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if ((byte >> 4) < MAX_REBOOT_CNT) {
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byte += 1 << 4; /* No, add 1 to the count */
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}
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else {
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byte &= 0xfc; /* Yes, put in fallback mode */
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}
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/* Is this the first boot? */
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if ((byte >> 4) <= 1) {
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byte = (byte & 0xfc) | ((byte & 1) << 1); /* yes, shift the boot bits */
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}
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/* Save the boot byte */
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cmos_write(byte, RTC_BOOT_BYTE);
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return ((byte >> 4) < MAX_REBOOT_CNT);
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}
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