OvmfPkg/README: document 4MB flash layout

[mirror_edk2.git] / OvmfPkg / README

diff --git a/OvmfPkg/README b/OvmfPkg/README
index 304e69fbe5456d57ae1e0d4bf95800b3a91b3793..33ff9432bb3ea42788344ad733260dadbaee3bba 100644 (file)
--- a/OvmfPkg/README
+++ b/OvmfPkg/README
@@ -245,15 +245,20 @@ longer.)
 \r
 === OVMF Flash Layout ===\r
 \r
-Like all current IA32/X64 system designs, OVMF's firmware\r
-device (rom/flash) appears in QEMU's physical address space\r
-just below 4GB (0x100000000).\r
+Like all current IA32/X64 system designs, OVMF's firmware device (rom/flash)\r
+appears in QEMU's physical address space just below 4GB (0x100000000).\r
 \r
-The layout of the firmware device in memory looks like:\r
+OVMF supports building a 1MB, 2MB or 4MB flash image (see the DSC files for the\r
+FD_SIZE_1MB, FD_SIZE_2MB, FD_SIZE_4MB build defines). The base address for the\r
+1MB image in QEMU physical memory is 0xfff00000. The base address for the 2MB\r
+image is 0xffe00000. The base address for the 4MB image is 0xffc00000.\r
+\r
+Using the 1MB or 2MB image, the layout of the firmware device in memory looks\r
+like:\r
 \r
 +--------------------------------------- 4GB (0x100000000)\r
 | VTF0 (16-bit reset code) and OVMF SEC\r
-| (SECFV)\r
+| (SECFV, 208KB/0x34000)\r
 +--------------------------------------- varies based on flash size\r
 |\r
 | Compressed main firmware image\r
@@ -271,9 +276,27 @@ The layout of the firmware device in memory looks like:
 | area (56KB/0xe000)\r
 +--------------------------------------- base address\r
 \r
-OVMF supports building a 1MB or a 2MB flash image. The base address for\r
-a 1MB image in QEMU physical memory is 0xfff00000. The base address for\r
-a 2MB image is 0xffe00000.\r
+Using the 4MB image, the layout of the firmware device in memory looks like:\r
+\r
++--------------------------------------- base + 0x400000 (4GB/0x100000000)\r
+| VTF0 (16-bit reset code) and OVMF SEC\r
+| (SECFV, 208KB/0x34000)\r
++--------------------------------------- base + 0x3cc000\r
+|\r
+| Compressed main firmware image\r
+| (FVMAIN_COMPACT, 3360KB/0x348000)\r
+|\r
++--------------------------------------- base + 0x84000\r
+| Fault-tolerant write (FTW)\r
+| Spare blocks (264KB/0x42000)\r
++--------------------------------------- base + 0x42000\r
+| FTW Work block (4KB/0x1000)\r
++--------------------------------------- base + 0x41000\r
+| Event log area (4KB/0x1000)\r
++--------------------------------------- base + 0x40000\r
+| Non-volatile variable storage\r
+| area (256KB/0x40000)\r
++--------------------------------------- base address (0xffc00000)\r
 \r
 The code in SECFV locates FVMAIN_COMPACT, and decompresses the\r
 main firmware (MAINFV) into RAM memory at address 0x800000. The\r