From 07da2163b3d8e84e4262bdd9fed03cb76116154e Mon Sep 17 00:00:00 2001 From: "Ronald G. Minnich" Date: Thu, 16 Jan 2003 21:35:59 +0000 Subject: [PATCH] info on flash. --- Documentation/flashfaq.txt | 40 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 40 insertions(+) create mode 100644 Documentation/flashfaq.txt diff --git a/Documentation/flashfaq.txt b/Documentation/flashfaq.txt new file mode 100644 index 0000000000..750b71f471 --- /dev/null +++ b/Documentation/flashfaq.txt @@ -0,0 +1,40 @@ + +This FAQ may be found in the LinuxBIOS source tree, under +Documentation/flashfaq.txt + +Q. What is FLASH? +A. FLASH is an electrically reprogrammable, read-only memory that saves +its contents across power cycles. FLASH currently comes in two general types, +asynchronous and synchronous. Currnently only Intel sells FLASH that is +synchronously read and written. + +Q. How is FLASH used in PCs? +A. FLASH is used for the BIOS software that boots the PC when it is turned on +or reset. FLASH contains the first software that the PC runs. + +Q. What are the typical sizes of FLASH in PCs +A. Strangely enough, the size of FLASH in PCs has been dropping in recent +years, after growing for several years. Early FLASH came in DIP-32 parts +and was 256KB or 512KB in size. BIOSes are now compressed and hence the size +has dropped to 256KB in recent years. + +Q. How is FLASH written? +A. On newer PCs the FLASH can be written entirely from software. No jumper +manipulation is required. Several programs are available on Linux to do this +rewriting, one of which is included in the LinuxBIOS source tree. + +Q. What are the obstacles to writing FLASH. +A. There are three levels of interlock to updating FLASH. First are interlocks +in the FLASH chips themselves. These typically require writing specific +patters to the chips in a specific order to unlock the write locks on +the chip. Second are interlocks built in to the PC chipset, which require +bits to be set in the chipset to make the FLASH part of the address space +writeable. These two interlocks are fairly easy to work with. +The third interlock is the hardest. Many motherboard vendors put additional +hardware interlocks external to the PC chipset onto the motherboard. These +interlocks are difficult to figure out (by design). They are occasionally +documented on embedded motherboards, but on most PC chipsets they are +obscured. These interlocks present the most challenging problems to those +wishing to use LinuxBIOS on their motherboard. + +