USB full speed device interface (USB) UM0306
448/519
Reception byte count n ()
Address Offset: [] + n*16 + 12
USB local Address: [] + n*8 + 6
This table location is used to store two different values, both required during packet
reception. The most significant bits contains the definition of allocated buffer size, to allow
buffer overflow detection, while the least significant part of this location is written back by the
USB Peripheral at the end of reception to give the actual number of received bytes. Due to
the restrictions on the number of available bits, buffer size is represented using the number
of allocated memory blocks, where block size can be selected to choose the trade-off
between fine-granularity/small-buffer and coarse-granularity/large-buffer. The size of
allocated buffer is a part of the endpoint descriptor and it is normally defined during the
enumeration process according to its maxPacketSize parameter value (See “Universal
Serial Bus Specification”).
Double-buffered and Isochronous OUT Endpoints have two
151413121110987654321 0
BLSIZE NUM_BLOCK[4:0] COUNTn_RX[9:0]
rwrwrwrwrwrwrrrrrrrrr r
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 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 ranges from 32 to 1024 bytes, which is the longest packet size
allowed by USB standard specifications.
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
Tabl e 6 3.
Bits 9:0
COUNTn_RX[9:0]: Reception Byte Count
These bits contain the number of bytes received by the endpoint associated with the
register during the last OUT/SETUP transaction addressed to it.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
BLSIZE
_1
NUM_BLOCK_1[4:0] COUNTn_RX_1[9:0]
rwrwrwrwrwrwrrrrrrrrr r
151413121110987654321 0
BLSIZE
_0
NUM_BLOCK_0[4:0] COUNTn_RX_0[9:0]
rwrwrwrwrwrwrrrrrrrrr r
To Next Page
Loading...
Need help?
General
