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> "Mark Sawyer" <[EMAIL PROTECTED]> 01/24/02 03:13PM > I realize that this is an issue of the media present > in the device but what is the preferred method > of determining sector size? Me, I don't have an answer here. There wasn't any clear protocol for this, last I checked. I'd love to hear different. I'm not clear myself on why Windows UDma connections to actual Cd-rw drives appear to work mostly. > My problem is > determining the correct sector size for CDROM's > when performing DMA. ... > In the case of PIO, > this is not a problem > since the device tells me how many bytes to expect. I'm writing just because I can share that using Dma in place of Pio is even tougher for other people: In the January 1998 revision of SFF 8090 (Mt Fuji), sorted in descending order by the largest power of two that is a factor, we see a Gcd (greatest common divisor) of 4, among these block sizes: x800 = 2048 = 1 * 2**11 x200 = 512 = 1 * 2**9 x940 = 2368 = 1 * 2**6 * 37 x920 = 2336 = 1 * 2**5 * 73 x990 = 2448 = 1 * 2**4 * 3**2 * 17 x930 = 2352 = 1 * 2**4 * 3 * 49 x808 = 2056 = 1 * 2**3 * 257 x924 = 2340 = 1 * 2**2 * 3**2 * 5 * 13 x91C = 2332 = 1 * 2**2 * 11 * 53 x914 = 2324 = 1 * 2**2 * 7 * 83 We see these by way of: If supported, block sizes (see See Block Descriptor Block Sizes for Read on page 234.) shall include 2048 and may include 512, 2056, 2324, 2332, 2336, 2340, 2352, 2368, and 2448 bytes. The Table of Block Sizes for Read shows the implementation of the various block sizes. Table 158 - Block Descriptor Block Sizes for Read Size Readable block types 512 Mode 1 or Mode 2 Form 1 sectors divided into four blocks each. 2048 Mode 1, Mode 2 Form 1, or DVD 2056 Mode 2 Form 1 with subheader. Equivalent to Read CD, Flag = 50h. 2324 Mode 2 Form 2 with no subheader. Note: There is no mapping to Read CD, as the 4 spare bytes are not returned. 2332 Mode 2, form 1 or 2 data. The drive shall operate as specified for 2048 byte blocks except: Both forms send 2332 byte blocks. Form 1 blocks return the third layer ECC with the user data. Note: There is no mapping to Read CD, as the 4 spare bytes are not returned. 2336 Mode 2 data The drive shall operate as specified for 2048 byte blocks lengths. This mode will include all data, including Yellow Book Mode 2 sectors and Form 1 and Form 2. Equivalent to Read CD, Flag = 58h. 2340 All bytes except the synchronization field. Equivalent to Read CD, Flag = 78h. 2352 Audio or raw blocks. The drive shall operate as specified for 2048 byte blocks. Reads of data mode sectors shall return descrambled data. Equivalent to Read CD, Flag = F8h. 2448 or 2368 Audio or raw blocks with raw sub-channel. The drive shall not perform the data descrambling operation. Equivalent to Read CD, Flag = F8, Sub-channel data selection = 010b (2448) or Sub-channel data selection = 001b (2368). ... Subscribe/Unsubscribe instructions can be found at www.t13.org.
