Cypress FX2LP - Manual (Page 5)

February 19, 2008 Document No. 001-15342 Rev. ** 5
AN6077
The firmware uses the AUTO mode for both IN and OUT
transfers. This means that the maximum size (512 bytes)
packets are committed automatically from the peripheral
domain to the USB domain for OUT transfers. For IN trans-
fers, they are committed from USB to the peripheral domain. The 8051 is not involved in committing packets. Short pack-
ets are handled by the master strobing the PKTEND of the
slave. In this implementation, the PKTEND of the slave is tied
to CTL2 of the master. So the GPIFIDLECTL register is writ-
ten to strobe PKTEND.
Psuedocode for Master OUT
if GPIF is IDLE
if there is a packet in EP2 OUT
if the peripheral is not FULL
trigger the GPIF Write Transaction
// handle short packet
if the transaction count < 512
if GPIF is IDLE
strobe PKTEND
else
// do nothing; wait for GPIF to be done
else
// do nothing; packet is not short packet
else
// do nothing; peripheral is FULL
else
// do nothing; no data is available to transfer
else
// do nothing; GPIF is not IDLE
Psuedocode for Master IN
if the GPIF is IDLE
if the peripheral is not empty
if EP6 IN is not full
trigger the GPIF Read transaction
if packet is short packet
commit the packet by writing INPKTEND
else
//do nothing; packet is not short
else
//do nothing; EP6 IN is full
else
//do nothing; the peripheral does not have data to transfer
else
//do nothing; GPIF is busy
Expanded Master OUT Code
if( GPIFTRIG & 0x80 )
{
// DONE=1, when GPIF is "idle"
// check if there is a packet in the peripheral domain (EP2OUT)
if( EP24FIFOFLGS & 0x02 )
{
// EF=1 when buffer "empty", for example, no more data to transfer
}
else
{
// EF=0, when slave fifo is "not empty"
// the cpu passed the packet to the peripheral domain (AUTO OUT)
// check if peripheral "not full"
if( GPIFREADYSTAT & 0x02 )
{
// RDY1=1, when peripheral is "not" FULL (tied to peripheral "full" flag)
// drive FIFOADDR lines
OEA = 0xC0;
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