isp1760 NXP Semiconductors, isp1760 Datasheet - Page 14

• Manufacturer Part Number: isp1760
• Description: Hi-speed Universal Serial Bus Host Controller For Embedded Applications
• Manufacturer: NXP Semiconductors

Philips Semiconductors
9397 750 13257
Product data sheet
7.2.2 Structure of the ISP1760 Host Controller memory
The total amount of memory allocated to the payload determines the maximum transfer
size specified by a PTD—a larger internal memory size results in less CPU interruption for
transfer programming. This means less time spent in context switching, resulting in better
CPU usage.
A larger buffer also implies a larger amount of data can be transferred. The transfer,
however, can be done over a longer period of time, to maintain the overall system
performance. Each transfer of the USB data on the USB bus can span for up to a few
milliseconds before requiring further CPU intervention for data movement.
The internal architecture of the ISP1760 allows a flexible definition of the memory buffer
for optimization of the data transfer on the CPU extension bus and the USB. It is possible
to implement various data transfer schemes, depending on the number and type of USB
devices present (for example: push-pull—data can be written to half of the memory while
data in the other half is being accessed by the Host Controller and sent on the USB bus).
This is useful especially when a high-bandwidth ‘continuous or periodic’ data flow is
required.
Through an analysis of the hardware and software environment regarding the usual data
flow and performance requirements of most embedded systems, Philips has determined
the optimal size for the internal buffer as approximately 64 kbytes.
The 63-kbyte internal memory consists of the PTD area and the payload area.
Both the PTD and payload memory zones are divided into three dedicated areas for each
main type of USB transfer: isochronous (ISO), interrupt (INT) and Acknowledged Transfer
List (ATL). As shown in
beginning of the memory, occupying the address range 0400h to 0FFFh, following the
address space of the registers. The payload or data area occupies the next memory
address range 1000h to FFFFh, meaning that 60 kbytes of memory are allocated for the
payload data.
A maximum of 32 PTD areas and their allocated payload areas can be defined for each
type of transfer. The structure of a PTD is similar for every transfer type and consists of
eight Double Words (DWs) that must be correctly programmed for a correct USB data
transfer. The reserved bits of a PTD must be set to logic 0. A detailed description of the
PTD structure can be found in
The transfer size specified by the PTD determines the contiguous USB data transfer that
can be performed without any CPU intervention. The respective payload memory area
must be equal to the transfer size defined. The maximum transfer size is flexible and can
be optimized, depending on the number and nature of USB devices or PTDs defined and
their respective MaxPacketSize.
The CPU will program the DMA to transfer the necessary data in the payload memory.
The next CPU intervention will be required only when the current transfer is completed
and DMA programming is necessary to transfer the next data payload. This is normally
signaled by the IRQ that is generated by the ISP1760 on completing the current PTD,
meaning all the data in the payload area was sent on the USB bus. The external IRQ
signal is asserted according to the settings in the IRQ Mask OR or IRQ Mask AND
registers, see
Section
Rev. 01 — 8 November 2004
8.4.
Table
3, the PTD areas for ISO, INT and ATL are grouped at the
Section
9.
Embedded Hi-Speed USB host controller
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
ISP1760
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