So it turns out the SCSI ReadCapacity10 command does not return the
device capacity. It returns the address of the last block, which is
(capacity - 1).
Also fixed Upstream's end-of-device sanity check.
Previously we wrote 4 x 64 byte transactions to the downstream device.
This is fast, but very occasionally the USB host silicon would bug out.
Reverting to single 64 byte write transactions increases reliability at
the expense of some write speed.
Upstream's edge-detect interrupt that starts SPI transmission was not
firing. Sometimes. On some boards only. The cause was Downstream not
allowing enough time between edges for Upstream to catch the signal.
Also misc code tidyups.
It turns out that suspend support on the STM32 USB core is buggy as
heck. Host mode cannot resume after suspend, and device mode cannot
receive resume or send wakeup signalling.
I managed to fake resume support by keeping Downstream and our connected
device running at full power, and simulating a wakeup event to the host
by disconnecting/reconnecting Upstream from the host.
It will sometimes NAK part-way through a multi-packet OUT URB. And what
it wants is for the host to resend beginning from the last even-numbered
packet. NOT the last packet it received, and NOT the beginning of that
URB.
It turned out we were getting a "device disconnected" interrupt while
waiting for the port to enable following reset. Simply ignoring the
disconnect interrupt allows everything to work! WTF...
...Downstream was not always changing state correctly after closely
spaced interrupts.
Also improve flash-write-lockout function to avoid dependency on
optimisation level.
Each USB transaction passed to the driver now consists of multiple
64-byte packets. 8 packets when receiving, 4 packets when transmitting.
The STM32 silicon bugs out when more than 4 packets are scheduled to
write at a time :(
Reads 1.0MB/sec, writes 967kB/sec, not CPU limited :)
Added timeout checks and retry functionality to control transaction
state machine. But some times the device just won't talk, so we flash
the fault LED slowly to give the user some clue about what happened.
Robert Fisk