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| This is a proposal for a simple flash emulation on QEMU/KVM.
| | PC System Flash emulation was added for QEMU in pc-1.1. |
| | |
| | =Flash Hardware= |
| | Uses CFI flash support in hw/pflash_cfi01.c. |
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| =Command line interface= | | =Command line interface= |
| To enable saving of the flash contents, a -flash
| | Usage of -bios and -pflash parameters as of pc-1.1: |
| a command line parameter would be added. This parameter
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| normally will override the -bios file usage.
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| | |
| <Pre>
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| -flash path path to filename for saving flash contents | |
| </Pre>
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| | |
| If the flash path does not exist, then the -bios file will be read to
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| initialize the flash contents. If the flash path does exist, then it
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| will be used instead of the -bios file contents.
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| | |
| =VM hardware interface=
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| ==Hardware resources==
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| The flash will be available as memory mapped io just below 0x100000000 (4GB). For example, if the -flash file was 0x100000 (1MB) in size, then the flash will be available in memory space from 0xfff00000 through 0xffffffff.
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| | |
| ==Normal reads==
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| The flash content can be read in 1, 2, 4 or 8 byte sizes like the
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| current read-only bios rom. The read accesses are not required to be aligned.
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| | |
| ==Programming interface==
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| Aside from normal flash read operations, the flash can be communicated
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| with via special sequences of memory read and write operations.
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| This interface supports 32-bit aligned 32-bit data operations as
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| well as 64-bit aligned 64-bit operations.
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| In the following examples, the address 0xfffffffc is used for 32-bit
| | {| class='wikitable' border=1 |
| examples, and 0xfffffff8 is used for 64-bit examples. However,
| | ! KVM enabled !! -pflash used !! -bios used !! Result |
| any properly aligned address can be used from 0x100000000-sizeof(bios.bin)
| | |- |
| up through 0xfffffff8 (for 64-bit operations) or 0xfffffffc (for 32-bit
| | |rowspan=3 | <Center>No</Center> |
| operations).
| | | <Center>Yes</Center> || <Center>-</Center> |
| | | -pflash parameter will be loaded as flash image just below 4GB. |
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| Only 1 flash communication operation can occur at one time. If any
| | 'bios.bin' and -bios parameter will be ''ignored''. |
| flash write occurs in another area of the flash, the the previous
| | |- |
| operation will be cancelled.
| | | <Center>No</Center> || <Center>No</Center> |
| | | 'bios.bin' will be used to create a read-only pflash drive. |
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| ===Entering flash communication mode===
| | A flash device is available, but it is read-only. |
| 32-bit access:
| | |- |
| <Pre> | | | <Center>No</Center> || <Center>Yes</Center> |
| write32(addr=0xfffffffc, data=0x5a5a5a5a)
| | | -bios parameter will be used to create a read-only pflash drive. |
| read32(addr=0xfffffffc) => returns 0xa5a5a5a5
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| </Pre> | |
| 64-bit access:
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| <Pre> | |
| write64(addr=0xfffffff8, data=0x5a5a5a5a5a5a5a5a)
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| read64(addr=0xfffffff8) => returns 0xa5a5a5a5a5a5a5a5
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| </Pre> | |
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|
| ===Program flash===
| | A flash device is available, but it is read-only. |
| * The flash must be in flash communication mode
| | |- |
| 32-bit access:
| | |rowspan=3 | <Center>Yes</Center> |
| <Pre> | | || <Center>Yes</Center> || <Center>-</Center> |
| write32(addr=0xfffffffc, data=0x0)
| | | An error message condition: |
| read32(addr=0xfffffffc) => returns current flash contents
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| write32(addr=0xfffffffc, data=new flash contents)
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| read32(addr=0xfffffffc) => returns new flash contents
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| read32(addr=0xfffffffc) => returns new flash contents ^ 0xffffffff
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| </Pre> | |
| 64-bit access:
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| <Pre> | |
| write64(addr=0xfffffff8, data=0x0)
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| read64(addr=0xfffffff8) => returns current flash contents
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| write64(addr=0xfffffff8, data=new flash contents)
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| read64(addr=0xfffffff8) => returns new flash contents
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| read64(addr=0xfffffff8) => returns new flash contents ^ 0xffffffffffffffff
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| </Pre> | |
| * Following a successful program operation, the flash will immediately return to normal read mode.
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|
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|
| ===Flash size read===
| | PC system firmware (pflash) not available |
| * The flash must be in flash communication mode
| | |- |
| 32-bit access:
| | || <Center>No</Center> || <Center>No</Center> |
| <Pre> | | | 'bios.bin' will be loaded as rom image. |
| write32(addr=0xfffffffc, data=0x1)
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| read32(addr=0xfffffffc) => returns the size of the flash device
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| read32(addr=0xfffffffc) => returns the flash size ^ 0xffffffff
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| </Pre> | |
| 64-bit access:
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| <Pre> | |
| write64(addr=0xfffffff8, data=0x1)
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| read64(addr=0xfffffff8) => returns the size of the flash device
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| read64(addr=0xfffffff8) => returns the flash size ^ 0xffffffffffffffff
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| </Pre> | |
| * Following a flash size read operation, the flash will immediately return to normal read mode.
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|
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| ===Interruptions===
| | No system flash is available. |
| * If the sequences above are not followed exactly, then the flash device should cancel the operation and immediately enter read mode.
| | |- |
| * If a non-aligned write operation or a 1 or 2 byte write occurs to the flash while a flash operation is in progress, then the current operation is immediately cancelled.
| | | <Center>No</Center> || <Center>Yes</Center> |
| * If a properly aligned write operation occurs to an different address or of a different size while another operation is in progress, then the current operation is immediately cancelled. If the write was the proper value to begin entering flash communication mode, then it will be accepted, and the sequence can proceed as a new operation.
| | | -bios parameter filename will be loaded as rom image. |
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| ==Examples==
| | No system flash is available. |
| * 32-bit flash write example at address 0xffff0000. Data: old=0x76543210, new=0xfedcba98
| | |} |
| <Pre>
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| write32(addr=0xffff0000, data=0x5a5a5a5a)
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| read32(addr=0xffff0000) => returns 0xa5a5a5a5
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| write32(addr=0xffff0000, data=0x0)
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| read32(addr=0xffff0000) => returns 0x76543210
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| write32(addr=0xffff0000, data=0xfedcba98)
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| read32(addr=0xffff0000) => returns 0xfedcba98
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| read32(addr=0xffff0000) => returns 0x01234567
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| </Pre>
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|
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| * 64-bit read flash size example at address 0xffff0000. Flash size=0x100000
| | ==pflash drives== |
| <Pre>
| | The flash image can be any drive image format supported by QEMU. |
| write64(addr=0xffff0000, data=0x5a5a5a5a5a5a5a5a)
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| read64(addr=0xffff0000) => returns 0xa5a5a5a5a5a5a5a5
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| write64(addr=0xffff0000, data=0x1)
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| read64(addr=0xffff0000) => returns 0x0000000000100000
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| read64(addr=0xffff0000) => returns 0xffffffffffefffff
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| </Pre>
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|
| =Why this complicated?=
| | There are two ways to add the pflash drive when launching qemu-system-i386 or qemu-system-x86_64: |
| Programming flash in this proposal is simplistic by real hardware standards. Yet, for a VM we could easily make the flash region use a simple read/write interface.
| | # Use the -pflash parameter |
| | # Use the -drive parameter with if=pflash |
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| The downside to this would be that buggy code which inadvertently writes to the flash region might very easily corrupt the flash image of the VM. With a little complexity required to write the flash, we guard against this issue in most cases.
| | [[Category:Completed feature pages]] |
