Hi, friends:

When I read the IRQ init code in intr_init(), I found ICW4_AT_MASTER is
0x05, and ICW4_AT_SLAVE is 0x01.

But I read the Intel 8259A doc and Ralf Brown's file, when bit 3 set as
0, there is no meaning for bit 2. So, it seems no difference for
ICW4_AT_MASTER and ICW4_AT_SLAVE, though bit 2 in ICW4_AT_MASTER is 1.

Can any body give me some points what's the diference ? for I see the
Linux code set all ICW4 as 0x1.