Retrieving images and headers
Headers and images are transferred to the host system via the SCSI Read command. The data can be transferred in one of three forms: header only, image only, or compound image, i.e., header with image. To determine the form, set the transfer type within the SCSI Read command.
The image can be read in one of two ways:
∙Read the header, then read the image.
∙Read the compound image .
IMPORTANT: The header should always be read before the image. The header contains information pertinent to the successful transfer of the image, e.g., image size, and should be read prior to reading the image.
The following table illustrates the results of one R ead command followed by another. Assume that Image 1 is followed by Image 2.
| Requested | Resultant |
Last Transfer | Transfer | Transfer |
|
|
|
Compound (Header 1 and Image | Compound | Header 2 |
1) |
| Image 2 |
|
|
|
Compound (Header 1 and Image | Header | Header 2 |
1) |
|
|
|
|
|
Compound (Header 1 and Image | Image | Image 2* |
1) |
|
|
|
|
|
Header 1 | Compound | Header 2** |
|
| Image 2 |
|
|
|
Header 1 | Header | Header 2** |
|
|
|
Header 1 | Image | Image 1 |
|
|
|
Image 1 | Compound | Header 2 |
|
| Image 2 |
|
|
|
Image 1 | Header | Header 2 |
|
|
|
Image 1 | Image | Image 2* |
|
|
|
*Note that Header 2 was not transferred. This is not recommended.
**Note that Image 1 was not transferred.
|