Hi,
the enclosed benign patch solves two independent problems with the AMD
Elan SC400 series of embedded CPUs (a 486 with DRAM controller, 8253,
dual 8259, 16550 and EPP on a single chip):
1. The on-chip 8253 is fed from a 1.8920MHz clock instead of the usual
1.9318MHz clock, so the clock would lose more than a second per minute.
(Jason Sodergren <jason@mugwump.taiga.com>, 21 Mar 2000)
2. The on-chip serial interface has a nasty bug:
the UART_LSR_THRE bit is delayed one bit clock after the interrupt
line is asserted, i.e. if the serial port is running at 1200 bps, and
the tranmitter becomes empty and causes an interupt, the interrupt is
signalled about a millisecond (1/1200second) _before_ the THRE bit is
set.
This means that when the interrupt handler is entered after the
interrupt, the THRE bit is still clear, the handler believes that
there is nothing to be done and returns.
(Christer Weinigel <wingel@hog.ctrl-c.liu.se>, 26 Nov 1998)
The patch allows the user to enable both fixes simultaneously by selecting
"AMD SC400/SC410 bug work-around" which appears right after the selection
of CPU type (if a 486 is selected).
cheers
Anders Larsen
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