[vortex] Tyan Thunder K7 S2462 Dual 3c59x

[Donald Becker]

On Wed, 16 Jan 2002, Bogdan Costescu wrote:

> On Tue, 15 Jan 2002, Donald Becker wrote:
> 
> > The problem vortex-diag has with reading the EEPROM is likely that the
> > board design is missing a bias resistor that allow the driver to figure
> > out the serial EEPROM address size, 6 or 8 bits.
> 
> But could this produce the output that Kirk obtained: the value which 
> might be at address (4k+3) is present also at addresses (4k), (4k+1) and 
> (4k+2) ?

Exactly that problem -- the lower two address bits are ignored.

Serial EEPROM are accessed by sending the address bits one at a time,
with highest address bit first.  The EEPROM responds by sending a
leading marker bit and then the sixteen data bits.

Since the driver doesn't know if the EEPROM uses 6 or 8 address bits, it
determines the size by either trying to read a location and verifying
the result, or sending out address bits and looking for the leading
data marker bit.

If the address size is incorrectly detected as 8 bits, the driver sends
out 8 address bits and only the first six are used by the EEPROM.  The
result is address 0..3 all refer to the physical location '0'.


Terminology:
  EEPROM
     Electrically Erasable Programmable Read Only Memory
     I use this to mean Serial EEPROM chips, 8 pin devices with the
     address and data transferred one bit at a time.  They hold only a
     64 or 256 entries of 16 bits each, just enough for basic
     configuration parameters
  Flash
     Technically also EEPROM.  These are chips with many address and
     data pins (28, 32 or 40 pins) that can hold an entire boot program.


Donald Becker				becker@scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Second Generation Beowulf Clusters
Annapolis MD 21403			410-990-9993