Siemens C541U, User Manual

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Semiconductor Group 6-49 1999-04-01
On-Chip Peripheral Components
C541U
6.4.3 USB Memory Buffer Organization
The address generation of the USB memory buffer is based on address offset and base address
pointer. This scheme allows flexible and application specific buffer allocation and management. The
length of an endpoint buffer can be up to 8, 16, 32, or 64 bytes. The start address of each endpoint
buffer can be located to memory locations according table 6-5.
In order to avoid unused memory space between two endpoint buffers, the largest buffer should be
located at the highest address. This structure should be used to allocate USB memory for all
endpoint buffers. The base address for the setup packet is always located at address 00
H
. This
leads to a typical USB buffer structure as shown in figure 6-31 with a buffer length of 64 bytes for
endpoint 2, 16 bytes for endpoints 1 and 3, 8 bytes for endpoint 0, and a predefined length of 8 bytes
for endpoint 0 and the setup token.
Figure 6-31
Endpoint Buffer Allocation (Example: 4 Endpoints)
Table 6-5
USB Buffer Length and Base Addresses Values
Buffer Length Valid Buffer Base Addresses
8 bytes 08H, 10H, 18H, 20H, 28H, 30H, 38H, 40H, 48H, 50H, 58H, 60H, 68H, 70H, 78H
16 bytes 10H, 20H, 30H, 40H, 50H, 60H, 70H
32 bytes 20H, 40H, 60H
64 bytes 40H
Endpoint 2 Buffer
Endpoint 2 Buffer
Endpoint 3 Buffer
Endpoint 1 Buffer
Setup Token
40
H
Buffer Block EPBAn EPLENn
Endpoint 2 EPBA2=08H EPLEN2=40H
Endpoint 3 EPBA3=06H EPLEN3=10H
Endpoint 1 EPBA1=04H EPLEN1=10H
Endpoint 0 EPBA0=03H EPLEN0=08H
Setup Token Adress 00H
on page 0 8 Bytes
7F
H
30
H
20
H
18
H
00
H
Endpoint 0 Buffer