EMERSON KJ4001X1-BA1功率控制器
POST映像應返回到引導加載程序，但不是必需的。返回后，引導加載程序繼續掃描可執行的備用引導映像。將控制權返回到引導加載程序的POST映像必須確保在返回時(shí)，板的狀態(tài)與POST進(jìn)入時(shí)板的狀態(tài)一致。USER映像不應將控制權返回到引導加載程序。6.7.5備用啟動(dòng)映像和安全啟動(dòng)MOTLoad的一些較新版本支持備用啟動(dòng)映像以及安全啟動(dòng)恢復過(guò)程。如果MVME7100上有安全啟動(dòng)，則支持備用啟動(dòng)映像。在支持備用引導映像的情況下，引導塊中的引導加載程序代碼檢查閃存庫的上8MB以查找備用引導映像。如果找到映像，則將控制權傳遞給映像。引導映像固件掃描通過(guò)檢查每個(gè)1MB邊界的一組定義的標志來(lái)執行掃描，這些標志將映像標識為POST、USER或備用MOTLoad。POST是用戶(hù)開(kāi)發(fā)的開(kāi)機自檢，它將執行一組診斷，然后返回引導加載程序映像。USER將是一個(gè)引導映像，例如VxWorks bootrom，它將執行板初始化?？梢龑У腣xWorks內核也可以是USER映像。引導映像的大小不限于1MB或更??；然而，它們必須從掃描閃存庫8MB內的1MB邊界開(kāi)始。
POST images are expected, but not required, to return to the boot loader. Upon return, the
boot loader proceeds with the scan for an executable alternate boot image. POST images
that return control to the boot loader must ensure that upon return, the state of the board is
consistent with the state that the board was in at POST entry. USER images should not
return control to the boot loader.
6.7.5 Alternate Boot Images and Safe Start
Some later versions of MOTLoad support alternate boot images and a safe start recovery
procedure. If safe start is available on the MVME7100, alternate boot images are
supported. With alternate boot image support, the boot loader code in the boot block
examines the upper 8MB of the flash bank for alternate boot images. If an image is found,
control is passed to the image.Boot Image Firmware Scan
The scan is performed by examining each 1MB boundary for a defined set of flags that
identify the image as being POST, USER, or Alternate MOTLoad. POST is a userdeveloped Power On Self Test that would perform a set of diagnostics and then return to
the boot loader image. USER would be a boot image, such as the VxWorks bootrom, which
would perform board initialization. A bootable VxWorks kernel would also be a USER
image. Boot images are not restricted to being 1MB or less in size; however, they must
begin on a 1MB boundary within the 8MB of the scanned flash bank.
