Sun 04-Aug-13 11:37 AM | edited Sun 04-Aug-13 11:41 AM by mirek21
>I don't believe the camera flash would be relevant. The clock >signal is sent on pin 5 to the SD cards by the SDIO chip and >the chip has the smarts, (ie, its own firmware), to determine >what kind of card it is talking to. It gets a base clock >signal of 25Mhz and has its own clock multipliers that it >controls based in the card it sees plugged in. The image >below is a basic block diagram. >
In real world capturing RAW images means more than transferring a stream data over SDIO line.
There are ~25MB data chunks that are being buffered in the camera memory. Camera and image processor need to add metadata, generate JPEG previews, etc. The RAM buffer is likely sharing the bus with the sensor, main CPU, image processor and the SDIO host controller and other parts. Any data transfers are likely protected by error correction schemes. On the other side of the SDIO, there is a flash controller thats need to be able to translate logical blocks to physical flash cells of one or more NAND flash chips. Taking into the account effects like write amplification, wear levelling, bad block management, overprovisioning, etc. On one level above there is a FAT32/ExFat filesystem thats translates cluster to logical blocks, generates filesystem metadata, etc.
To sum up it is a rather complex system and there could be several performance limiting factors that limits RAW performance. In reality we see that it is not possible to write 45 MB of data in exactly 1 sec to 45mb/s rated card, despite of having 100 MHz SDIO signalling speed. Just as nobody expects to be able to write 1000 bits of data per seconds on a gigabit ethernet.
I don't say that the D600 is capable of storing data to card faster than 50 MB/s. Most likely it is not as shown in the data sheet. However, in reality the 45mb/s rated cards are well below 45 MB/s of RAW writing speed and 90-95 MB/s rated cards still show measurable benefits compared to 45 MB/s cards.
>So to be clear, you are holding down the shutter button, >waiting and counting frames for the buffer to fill and timing >the results with a stopwatch?