RM0367 Rev 7 953/1043
RM0367 Universal serial bus full-speed device interface (USB)
955
enumeration process according to its maxPacketSize parameter value (See “Universal
Serial Bus Specification”).
Bit 15 BL_SIZE: Block size
This bit selects the size of memory block used to define the allocated buffer area.
– If BL_SIZE=0, the memory block is 2-byte large, which is the minimum block
allowed in a half-word wide memory. With this block size the allocated buffer size
ranges from 2 to 62 bytes.
– If BL_SIZE=1, the memory block is 32-byte large, which allows to reach the
maximum packet length defined by USB specifications. With this block size the
allocated buffer size theoretically ranges from 32 to 1024 bytes, which is the longest
packet size allowed by USB standard specifications. However, the applicable size is
limited by the available buffer memory.
Bits 14:10 NUM_BLOCK[4:0]: Number of blocks
These bits define the number of memory blocks allocated to this packet buffer. The actual
amount of allocated memory depends on the BL_SIZE value as illustrated in Table 170.
Bits 9:0 COUNTn_RX[9:0]: Reception byte count
These bits contain the number of bytes received by the endpoint associated with the
USB_EPnR register during the last OUT/SETUP transaction addressed to it.
Table 170. Definition of allocated buffer memory
Value of
NUM_BLOCK[4:0]
Memory allocated
when BL_SIZE=0
Memory allocated
when BL_SIZE=1
0 (‘00000) Not allowed 32 bytes
1 (‘00001) 2 bytes 64 bytes
2 (‘00010) 4 bytes 96 bytes
3 (‘00011) 6 bytes 128 bytes
... ... ...
14 (‘01110) 28 bytes 480 bytes
15 (‘01111) 30 bytes
16 (‘10000) 32 bytes
... ... ...
29 (‘11101) 58 bytes
30 (‘11110) 60 bytes
31 (‘11111) 62 bytes N/A
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