HS_USB2.0 host
RM0082
414/844
Doc ID 018672 Rev 1
According to its functionality, the PBUF block interface with both the List Processor and the
Root Hub. Specifically, during an OUT transaction, the List Processor fetches data from the
system memory and writes them in the PBUF. Besides, during an IN transaction, the data
are written to PBUF by the Root Hub
.
The Packet Buffer size depends on the system latency and bandwidth allocated to the EHCI
Host Controller. For example, in case PBUF size is programmed to 64 bytes, a 1024-bytes
IN transfer would get 1024/64 = 16 data transfer on the AHB bus. If the system is not able to
ensure EHCI access to AHB bus for these 16 transfers with no breaks, then a buffer overrun
occurs. In this case, to avoid buffer overrun or under-run, PBUF size could be set to 1024
bytes.
22.4.5 Root
hub
The Root Hub (RH) block interfaces between the List Processor and the USB PHY. It
propagates reset and resume signals to downstream ports, and handles port connections
and disconnections.
The RH operates both on the local PHY clock (a free-running 30/60 MHz clock) and on the
clock source from each physical port (30 MHz with a 16 bit interface).
22.5
OHCI host controller blocks
The USB Open Host Controller is designed to be independent of the Bus Interface Unit
(BIU) as in
. The host bus is assumed to be at least 32 bits wide with adequate
performance to support the data rate of the particular implementation (100Mbit/sec or
higher plus overhead for DMA structures) as well as bounded latency so that the FIFO’s can
have a reasonable size.