Re: [SeaBIOS] How much RAM is required?
Markus Armbruster arm...@redhat.com writes: Kevin O'Connor ke...@koconnor.net writes: On Fri, Aug 10, 2012 at 04:54:06PM +0200, Markus Armbruster wrote: Peter Stuge pe...@stuge.se writes: Markus Armbruster wrote: Could SeaBIOS fail more cleanly when it detects insufficient RAM? What would you propose? Fail POST with panic(Not enough RAM)? The amount of memory is communicated from QEMU to SeaBIOS via nvram variables. As far as I know, those variables can only communicate ram sizes in 1meg chunks - so there is no way to communicate (and/or detect) a ramsize of under 1 meg. Not true, the variables *can* communicate more. Here's what QEMU stores in the RTC's NVRAM (CMOS memory) on RAM: addr size meaning [unit] 0x15 2 base memory (below 1MiB) [KiB] 0x17 2 extended memory (between 1MiB and 64MiB) [KiB] 0x30 2 copy of 0x17/0x18 0x34 2 memory between 16MiB and 4GiB [64KiB] 0x5b 3 memory above 4GiB [64KiB] Thus, memory sizes up to 16MiB can be declared with 1KiB granularity, and up to 1TiB with 64KiB granularity. Note that RAM 0xa..0xf is inaccessible. However, the values QEMU *currently* stores are buggy for RAM sizes under 640KiB: base memory is set to 640KiB, and extended memory underflows. Code is pc_cmos_init() in hw/pc.c. I'll try to get that fixed, either by storing correct values, or by enforcing a 1MiB minimum. 1MiB minimum was rejected. Instead, QEMU 1.2 got this fix: commit e89001f72edde37fb36fa7c964daa1bbeb2eca26 Author: Markus Armbruster arm...@redhat.com Date: Wed Aug 15 13:12:20 2012 +0200 pc: Fix RTC CMOS info on RAM for ram_size 1MiB pc_cmos_init() always claims 640KiB base memory, and ram_size - 1MiB extended memory. The latter can underflow to lots of extended memory. Fix both, and clean up some. Note: SeaBIOS currently requires 1MiB of RAM, and doesn't check whether it got enough. [...] ___ SeaBIOS mailing list SeaBIOS@seabios.org http://www.seabios.org/mailman/listinfo/seabios
Re: [SeaBIOS] How much RAM is required?
Kevin O'Connor ke...@koconnor.net writes: On Fri, Aug 10, 2012 at 04:54:06PM +0200, Markus Armbruster wrote: Peter Stuge pe...@stuge.se writes: Markus Armbruster wrote: Could SeaBIOS fail more cleanly when it detects insufficient RAM? What would you propose? Fail POST with panic(Not enough RAM)? The amount of memory is communicated from QEMU to SeaBIOS via nvram variables. As far as I know, those variables can only communicate ram sizes in 1meg chunks - so there is no way to communicate (and/or detect) a ramsize of under 1 meg. Not true, the variables *can* communicate more. Here's what QEMU stores in the RTC's NVRAM (CMOS memory) on RAM: addr size meaning [unit] 0x15 2 base memory (below 1MiB) [KiB] 0x17 2 extended memory (between 1MiB and 64MiB) [KiB] 0x30 2 copy of 0x17/0x18 0x34 2 memory between 16MiB and 4GiB [64KiB] 0x5b 3 memory above 4GiB [64KiB] Thus, memory sizes up to 16MiB can be declared with 1KiB granularity, and up to 1TiB with 64KiB granularity. Note that RAM 0xa..0xf is inaccessible. However, the values QEMU *currently* stores are buggy for RAM sizes under 640KiB: base memory is set to 640KiB, and extended memory underflows. Code is pc_cmos_init() in hw/pc.c. I'll try to get that fixed, either by storing correct values, or by enforcing a 1MiB minimum. Here's how SeaBIOS uses this information, in ram_probe(): 1. read memory above 16MiB from 0x34/0x35. 2. if non-zero, add 16MiB, else read memory between 1MiB and 64MiB from 0x30/0x31, add 1MiB 3. read memory above 4GiB SeaBIOS doesn't read 0x15/0x16 at all. However, this SeaBIOS shortcoming is currently masked by the QEMU bug. ___ SeaBIOS mailing list SeaBIOS@seabios.org http://www.seabios.org/mailman/listinfo/seabios
Re: [SeaBIOS] How much RAM is required?
On Fri, Aug 10, 2012 at 04:54:06PM +0200, Markus Armbruster wrote: Peter Stuge pe...@stuge.se writes: Markus Armbruster wrote: Could SeaBIOS fail more cleanly when it detects insufficient RAM? What would you propose? Fail POST with panic(Not enough RAM)? The amount of memory is communicated from QEMU to SeaBIOS via nvram variables. As far as I know, those variables can only communicate ram sizes in 1meg chunks - so there is no way to communicate (and/or detect) a ramsize of under 1 meg. -Kevin ___ SeaBIOS mailing list SeaBIOS@seabios.org http://www.seabios.org/mailman/listinfo/seabios
Re: [SeaBIOS] How much RAM is required?
Markus Armbruster wrote: SeaBIOS requires a minimum of 1Meg of ram. I didn't even know one could request less than 1meg of ram from QEMU. I'll cook up a QEMU patch to give it at least that much. But QEMU may use other firmware/payload than SeaBIOS which might require less than 1 MB of RAM. Good point. I disagree actually. It is not an invalid point, but please optimize for the common case and let's deal with microscopic corner cases if they actually happen. Could SeaBIOS fail more cleanly when it detects insufficient RAM? What would you propose? //Peter ___ SeaBIOS mailing list SeaBIOS@seabios.org http://www.seabios.org/mailman/listinfo/seabios
Re: [SeaBIOS] How much RAM is required?
Fred . wrote: No, I am not. Ok, so there's only a hypothesis. But I believe QEMU does have the functionality to load an arbitrary firmware. So the firmware doesn't necessarily have to be SeaBIOS. As you may know the 8086 reset vector is at 1MB-16 so it will be really difficult to run a PC-like machine with less than 1MB of memory. I don't believe one has ever existed. Don't know if its possible to make QEMU use an UEFI or OpenFirmware image instead, or if such an image exists. Sure, but UEFI rather requires 1GB than 1MB. //Peter ___ SeaBIOS mailing list SeaBIOS@seabios.org http://www.seabios.org/mailman/listinfo/seabios
Re: [SeaBIOS] How much RAM is required?
Peter Stuge pe...@stuge.se writes: Markus Armbruster wrote: SeaBIOS requires a minimum of 1Meg of ram. I didn't even know one could request less than 1meg of ram from QEMU. I'll cook up a QEMU patch to give it at least that much. But QEMU may use other firmware/payload than SeaBIOS which might require less than 1 MB of RAM. Good point. I disagree actually. It is not an invalid point, but please optimize for the common case and let's deal with microscopic corner cases if they actually happen. Could SeaBIOS fail more cleanly when it detects insufficient RAM? What would you propose? Fail POST with panic(Not enough RAM)? Perfect score if can limit ourselves to just ROM, registers, and possibly CPU cache, but no RAM, before this check. It's been done elsewhere, but it may not be practical for us. If we can't, we merely reduce the need this much RAM to avoid silent failure limit to something pretty much any conceivable firmware will require. QEMU might be more willing to enforce such a low limit. Making it enforce 1MiB will be a hard sell, I'm afraid... ___ SeaBIOS mailing list SeaBIOS@seabios.org http://www.seabios.org/mailman/listinfo/seabios
Re: [SeaBIOS] How much RAM is required?
Some machines also have broken memory modules. So some computers have 0 byte RAM in that case. :D On Fri, Aug 10, 2012 at 5:28 PM, Markus Armbruster arm...@redhat.com wrote: Frediano Ziglio frediano.zig...@citrix.com writes: On Fri, 2012-08-10 at 16:24 +0200, Peter Stuge wrote: Fred . wrote: No, I am not. Ok, so there's only a hypothesis. But I believe QEMU does have the functionality to load an arbitrary firmware. So the firmware doesn't necessarily have to be SeaBIOS. As you may know the 8086 reset vector is at 1MB-16 so it will be really difficult to run a PC-like machine with less than 1MB of memory. I don't believe one has ever existed. I remember that my manual of the NEC V20 (a 8086 clone with 10 MHZ!) has settings for 256KB of RAM (jumpers of course!) The ROM was mapped (physically!) at f with extended ROM at e. According to Wikipedia, the original IBM PC was sold with as little as 16KiB RAM. IIRC, 64KiB BIOS ROM at the top of the 1MiB address space. http://en.wikipedia.org/wiki/IBM_PC [...] ___ SeaBIOS mailing list SeaBIOS@seabios.org http://www.seabios.org/mailman/listinfo/seabios ___ SeaBIOS mailing list SeaBIOS@seabios.org http://www.seabios.org/mailman/listinfo/seabios
Re: [SeaBIOS] How much RAM is required?
Fred . eldman...@gmail.com writes: On Fri, Aug 10, 2012 at 5:28 PM, Markus Armbruster arm...@redhat.com wrote: Frediano Ziglio frediano.zig...@citrix.com writes: On Fri, 2012-08-10 at 16:24 +0200, Peter Stuge wrote: Fred . wrote: No, I am not. Ok, so there's only a hypothesis. But I believe QEMU does have the functionality to load an arbitrary firmware. So the firmware doesn't necessarily have to be SeaBIOS. As you may know the 8086 reset vector is at 1MB-16 so it will be really difficult to run a PC-like machine with less than 1MB of memory. I don't believe one has ever existed. I remember that my manual of the NEC V20 (a 8086 clone with 10 MHZ!) has settings for 256KB of RAM (jumpers of course!) The ROM was mapped (physically!) at f with extended ROM at e. According to Wikipedia, the original IBM PC was sold with as little as 16KiB RAM. IIRC, 64KiB BIOS ROM at the top of the 1MiB address space. http://en.wikipedia.org/wiki/IBM_PC [...] Some machines also have broken memory modules. So some computers have 0 byte RAM in that case. :D Yup, be we *can* catch that in QEMU :) ___ SeaBIOS mailing list SeaBIOS@seabios.org http://www.seabios.org/mailman/listinfo/seabios
Re: [SeaBIOS] How much RAM is required?
But QEMU may use other firmware/payload than SeaBIOS which might require less than 1 MB of RAM. On Thu, Aug 9, 2012 at 10:15 AM, Markus Armbruster arm...@redhat.com wrote: Kevin O'Connor ke...@koconnor.net writes: On Wed, Aug 08, 2012 at 01:50:13PM +0200, Markus Armbruster wrote: Watch this: $ qemu-system-x86_64 -nodefaults -vnc :0 -monitor stdio -m 16k QEMU 1.1.50 monitor - type 'help' for more information (qemu) qemu: fatal: Trying to execute code outside RAM or ROM at 0x4000 Admittedly a silly thing to try. I don't really expect SeaBIOS to work with 16KiB of RAM. But I'm curious: how much does it require? SeaBIOS requires a minimum of 1Meg of ram. I didn't even know one could request less than 1meg of ram from QEMU. I'll cook up a QEMU patch to give it at least that much. Thanks! ___ SeaBIOS mailing list SeaBIOS@seabios.org http://www.seabios.org/mailman/listinfo/seabios ___ SeaBIOS mailing list SeaBIOS@seabios.org http://www.seabios.org/mailman/listinfo/seabios
Re: [SeaBIOS] How much RAM is required?
No, I am not. But I believe QEMU does have the functionality to load an arbitrary firmware. So the firmware doesn't necessarily have to be SeaBIOS. Don't know if its possible to make QEMU use an UEFI or OpenFirmware image instead, or if such an image exists. On Thu, Aug 9, 2012 at 2:59 PM, Peter Stuge pe...@stuge.se wrote: Fred . wrote: But QEMU may use other firmware/payload than SeaBIOS which might require less than 1 MB of RAM. Really? Are you working on one? //Peter ___ SeaBIOS mailing list SeaBIOS@seabios.org http://www.seabios.org/mailman/listinfo/seabios ___ SeaBIOS mailing list SeaBIOS@seabios.org http://www.seabios.org/mailman/listinfo/seabios
[SeaBIOS] How much RAM is required?
Watch this: $ qemu-system-x86_64 -nodefaults -vnc :0 -monitor stdio -m 16k QEMU 1.1.50 monitor - type 'help' for more information (qemu) qemu: fatal: Trying to execute code outside RAM or ROM at 0x4000 Admittedly a silly thing to try. I don't really expect SeaBIOS to work with 16KiB of RAM. But I'm curious: how much does it require? ___ SeaBIOS mailing list SeaBIOS@seabios.org http://www.seabios.org/mailman/listinfo/seabios
Re: [SeaBIOS] How much RAM is required?
On Wed, Aug 08, 2012 at 01:50:13PM +0200, Markus Armbruster wrote: Watch this: $ qemu-system-x86_64 -nodefaults -vnc :0 -monitor stdio -m 16k QEMU 1.1.50 monitor - type 'help' for more information (qemu) qemu: fatal: Trying to execute code outside RAM or ROM at 0x4000 Admittedly a silly thing to try. I don't really expect SeaBIOS to work with 16KiB of RAM. But I'm curious: how much does it require? SeaBIOS requires a minimum of 1Meg of ram. I didn't even know one could request less than 1meg of ram from QEMU. -Kevin ___ SeaBIOS mailing list SeaBIOS@seabios.org http://www.seabios.org/mailman/listinfo/seabios
