| There's no doubt that the digital still camera (DSC) | | | | a significant degradation in the consumer experience |
| revolutionized the photography industry. The ability to | | | | in the past, the large amounts of data transferred |
| easily review, edit, and share photos has proven to | | | | with larger file sizes are now causing increased |
| be a significant advantage for consumers. As | | | | challenges in the number of pictures that can be |
| consumers and professionals became savvier with | | | | taken in multi-shot mode. The buffers in the DSCs |
| digital photo editing and publishing, the need for higher | | | | are filling up at a much faster rate, which in turn limits |
| resolution pictures also grew. DSCs started to | | | | the number of photos that can be stored. |
| increase the resolution of the pictures they were | | | | For example, some high end DSCs can shoot up to |
| capable of capturing in order to meet this demand, | | | | 10 pictures/second in multi-shot mode. With raw |
| with resolutions of 10 Megapixels not uncommon | | | | picture formats up to 20 MB, this would translate to |
| today. | | | | 200 MB/s of data being written to the SDRAM. Given |
| For maximum photo quality and photo manipulation | | | | an SDRAM size of 512 MB, the SDRAM buffer would |
| flexibility, some DSCs also feature raw uncompressed | | | | be full after just 2 seconds of shooting pictures. The |
| "digital negative" formats. The result of increasing | | | | storage interfaces found on DSCs today provide a |
| photo quality and resolution has also led to increasing | | | | typical transfer rate from the buffer to the storage |
| file sizes, which can reach upwards of 20 MB in size. | | | | of 5 MB/s, clearly leading to a bottleneck when |
| To accommodate these increasing files sizes, | | | | writing to storage. Once the buffer becomes full, the |
| memory storage sizes have also been increasing. | | | | camera would stop taking pictures until the data has |
| With the larger memory capacities, consumers have | | | | been written to storage and the buffer has been |
| been able to maintain, or increase the number of | | | | emptied. |
| photographs they may take for a given storage | | | | To enable more pictures to be taken in multi-shot |
| medium. | | | | mode, a designer could either increase the size of the |
| While increasing storage capacities have solved the | | | | SDRAM buffer, or deploy a method to write to |
| photo storage challenge, new challenges arise. DSCs | | | | storage faster. Increasing the size of the SDRAM |
| have not been optimized to handle the processing | | | | buffer can be a costly solution, thus it is worthwhile |
| and transfer of such large amounts of data. The first | | | | to explore solutions to improve the transfer time to |
| challenge lies in transferring large amounts of data to | | | | storage. |
| a PC for editing, printing, or publishing. While USB has | | | | West Bridge Architecture |
| become the de facto standard for connecting a DSC | | | | In 2006, Cypress Semiconductor introduced the |
| to a PC, the USB performance in DSC's may not | | | | West Bridge architecture. Similar to the North Bridge |
| have been optimized for handling large amounts of | | | | and South Bridge in PC architectures, the West |
| data. To illustrate, the graph in Figure 1 below shows | | | | Bridge was introduced to allow embedded processors |
| USB transfer times for a few of the DSCs available | | | | to evolve independently from quickly changing |
| on the market today. | | | | memory and peripheral interfaces. The West Bridge is |
| Transfer times can take from 2.5 min upwards to 16 | | | | designed as a companion chip to an embedded |
| min for 950 MB, translating to transfer rates of 6 | | | | processor to free it from data-intensive operations. |
| MB/s to under 1 MB/s. With more users transferring | | | | Processor intensive functions, such as USB or mass |
| larger amounts of data, consumers will not tolerate | | | | storage control, may be offloaded to a West Bridge |
| longer wait times for the data transfer. | | | | for maximum performance. In a DSC, a West Bridge |
| Longer transfer times also have the side effect of | | | | can be used to address the two discussed challenges |
| increasing the battery drain on the DSC. DSCs today | | | | faced by DSCs today. |
| do not charge while connected to a PC, therefore | | | | A West Bridge consists of three ports: one for |
| the longer a DSC stays connected to a PC, the more | | | | connecting to the processor, one for connecting to |
| battery drain occurs. For a consumer, one of the | | | | mass storage, and one for USB for external |
| most frustrating experiences while using a DSC would | | | | connections. Since the West Bridge consists of both |
| be to have the battery drain completely during a file | | | | USB and mass storage control, a direct path from |
| transfer. | | | | mass storage to USB is provided, thus offloading the |
| With consumer demand for transfer times in | | | | main processor, and providing for maximum USB |
| seconds, and not minutes, transfer rates of less than | | | | performance. Consumer devices using Cypress' West |
| 10 MB/s are no longer acceptable in order to achieve | | | | Bridge Antioch, have been tested to reach USB |
| acceptable transfer times. To understand the reasons | | | | transfer speeds up to 18 MB/s. At that transfer rate, |
| for the current slow transfer rates, it is useful to | | | | 950 MB of pictures would take just 53 seconds, |
| take a closer look at the data transfer path when | | | | enabling the best consumer experience when |
| copying files from the DSC to the PC. | | | | transferring photos |
| Most DSCs today feature removable storage in | | | | The independent three-port nature of the West |
| popular formats such as SD or Compact Flash. The | | | | Bridge also enables high performance transfers from |
| removable storage is typically connected directly to | | | | the processor to mass storage. With flexible high |
| the processor via the corresponding storage | | | | speed interfaces and a dedicated mass storage |
| controller. To copy files from the DSC to a PC, the | | | | controller on the West Bridge, performance of up to |
| data is first accessed from the removable storage by | | | | 20 MB/s writing to storage has been achieved. By |
| the processor. Next, it is buffered into SDRAM, | | | | writing to storage at the maximum rate, the DSC is |
| before it is sent to the PC via USB. This data path is | | | | able to empty its SDRAM buffer at a faster rate. In |
| not straightforward, and thus impacts the USB | | | | a DSC's multi-shot mode, faster writes to storage |
| performance. | | | | would reduce the bottleneck which can occur. A user |
| The second challenge that arises with increasing file | | | | would thus be able to take more photos under |
| sizes is in regards to a DSC's multi-shot mode. | | | | multi-shot mode than they could without a West |
| Multi-shot mode is a feature enabled on many DSCs | | | | Bridge architecture. |
| which allow a user to take multiple pictures in quick | | | | Conclusion |
| succession. Multi-shot mode is used commonly for | | | | With average DSC processor life cycles spanning |
| action shots, where it's desirable to capture many | | | | years, the challenge of keeping up with the latest |
| pictures in a short time span. | | | | consumer demands becomes a significant issue. It is |
| In multi-shot mode, pictures are captured in rapid | | | | clear that picture quality, resolution, and size will only |
| succession and buffered into SDRAM while images | | | | continue to increase as consumers and professionals |
| are written to storage. As writing to storage is | | | | alike strive for the best quality photographs possible. |
| slower than the rate at which the pictures are being | | | | With the new challenges brought forth in an ever |
| taken, the DSC will stop taking pictures once the | | | | changing market, a West Bridge architecture can be |
| SDRAM buffer is full. While this may not have caused | | | | adopted to best meet consumer requirements. |