Toshiba H1 Series Data Book page 448

(b) Dual packet mode
In dual packet mode, FIFO is divided into A and B packet, it is controlled
according to priority in hardware. It can be performed at once, transmitting and
receiving data to USB host and exchanges to external of UDC. When it reads out
data from FIFO for receiving, confirm condition of two packets, and consider the
order of priority. If it has received data to two packets, UDC outputs from first
receiving data by FIFO that can be accessed are common in two packets.
DATASIZE register is prepared every packet A and packet B. First, CPU must
recognize data number of first receiving packet by PACKET_ACTIVE bit. If
PACKET_ACTIVE bit was set to 1, that packet is received, first. Packet A and
packet B set data turn about always.
Below is this sequence.
Wait receiving data
DATASET register
DATASET = 0
DATASET register
• Check bit of EPx_DSET_A
• Check bit of EPx_DSET_B
DATASET = 1
SIZE register
• Read size of receiving data from applicable endpoint
• There is below 3 cases by setting bit of DATASET
Only A: Read number of sizeA register
Only B: Read number of sizeB register
Both of A and B: Read number of sizeA + B register
• Clear receiving data in FIFO
• Clear applicable bit in DATASET register
Figure 3.16.17 Receiving Sequence in Dual Packet Mode
IDLE
Receiving valid data
• Set bit of EPx_DSET_A (B)
• Assert EPx_DATASET signal
Interrupt by EPx_FULL_A (B)
Check DATASET register
• Confirm Size of SIZE_A_L
• Confirm Size of SIZE_A_H
• Confirm Size of SIZE_B_L
• Confirm Size of SIZE_B_H
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