BCC, ELKS 24 Bit addressing mode
Dear All,
I am porting ELKS to a special version of 80186 to be used in embedded devices. This special version known as Turbo186 is using 24 bit addressing using a special addressing scheme. So I need to modify bcc or as86 to support 24 bit addressing mode.
This type of operation is common in embedded usage. 24 bit addressing is working like this,
In normal 20 bit addressing when far jumps are used, two 16 bit operands are given for address calculation. First operand is left shifted 4 bits and added to second operand, then 20 bit address is calculated.
In 24 bit addressing mode, first operand is left shifted 8 bits and added to second operand, resulting in 24 bit address.
What am I required to do to support 24 bits addressing in bcc? Can you give me some insight or guide me to the correct person?
Thank you for your consideration and help.
Kindest regards,
Serdar Sutay
Quoted 14 lines · Serdar Sutay
Dear All,
I am porting ELKS to a special version of 80186 to be used in embedded devices. This special version known as Turbo186 is using 24 bit addressing using a special addressing scheme. So I need to modify bcc or as86 to support 24 bit addressing mode.
This type of operation is common in embedded usage. 24 bit addressing is working like this,
In normal 20 bit addressing when far jumps are used, two 16 bit operands are given for address calculation. First operand is left shifted 4 bits and added to second operand, then 20 bit address is calculated.
In 24 bit addressing mode, first operand is left shifted 8 bits and added to second operand, resulting in 24 bit address.
What am I required to do to support 24 bits addressing in bcc? Can you give me some insight or guide me to the correct person?
Thank you for your consideration and help.
Quoted 8 lines
Kindest regards,
Serdar Sutay
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Basically you're working with a 286 that's been lobotmized down to a 186 with the addressing features in place?
Quoted 18 lines · Segin
Quoted 16 lines · Serdar Sutay
Dear All,
I am porting ELKS to a special version of 80186 to be used in embedded devices. This special version known as Turbo186 is using 24 bit addressing using a special addressing scheme. So I need to modify bcc or as86 to support 24 bit addressing mode.
This type of operation is common in embedded usage. 24 bit addressing is working like this,
In normal 20 bit addressing when far jumps are used, two 16 bit operands are given for address calculation. First operand is left shifted 4 bits and added to second operand, then 20 bit address is calculated.
In 24 bit addressing mode, first operand is left shifted 8 bits and added to second operand, resulting in 24 bit address.
What am I required to do to support 24 bits addressing in bcc? Can you give me some insight or guide me to the correct person?
Thank you for your consideration and help.
Kindest regards,
Quoted 9 lines
Quoted 6 lines
Serdar Sutay
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More majordomo info at http://vger.kernel.org/majordomo-info.htmlBasically you're working with a 286 that's been lobotmized down to a 186 with the addressing features in place?
yes, but I need to address 16 Mbytes of RAM so I need to use 24 bit addressing mode.
Can Bcc compiler handle this automatically?
Quoted 4 lines
Quoted 3 lines
Basically you're working with a 286 that's been lobotmized down to a 186 with the addressing features in place?
yes, but I need to address 16 Mbytes of RAM so I need to use 24 bit addressing mode.
I hate to ask, but why bother with a 186 in the first place? As I understand it, the only real difference (other than some hardware integration) between the two is that the 286 has a 24 bit address space....which you'd need if you're going to use 16M of RAM anyway.
Dan
186 CPUs have various non-CPU functionality integrated into the chip itself, which is one reason it's popular in some embedded designs.
Quoted 14 lines · Dan Olson
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Quoted 3 lines
Basically you're working with a 286 that's been lobotmized down to a 186 with the addressing features in place?
yes, but I need to address 16 Mbytes of RAM so I need to use 24 bit addressing mode.
I hate to ask, but why bother with a 186 in the first place? As I understand it, the only real difference (other than some hardware integration) between the two is that the 286 has a 24 bit address space....which you'd need if you're going to use 16M of RAM anyway.
Dan
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True, I undesrstand, I just thought that the extra banking logic needed and the software overhead might negate that added integration, but I'm not sure what your goal is in the project. I've got some 186 CPUs sitting around if you have any need for a couple.
Dan
Quoted 22 lines · Jody
186 CPUs have various non-CPU functionality integrated into the chip itself, which is one reason it's popular in some embedded designs.
Quoted 6 lines · Dan Olson
Quoted 4 lines
Quoted 3 lines
Basically you're working with a 286 that's been lobotmized down to a 186 with the addressing features in place?
yes, but I need to address 16 Mbytes of RAM so I need to use 24 bit addressing mode.
Quoted 8 lines
I hate to ask, but why bother with a 186 in the first place? As I understand it, the only real difference (other than some hardware integration) between the two is that the 286 has a 24 bit address space....which you'd need if you're going to use 16M of RAM anyway.
Dan
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Hello!
As for your problems, sir, I also am interested. Please keep us advised.
As it happens, Dan Olson, I do have a need for some. Not too many. What do we need to do to arrange this transaction?
---
Gregg C Levine obiwanthejediknight atsign att dot net
"The Force will be with you. Always."
----- Original Message -----
From: "Dan Olson" <[email protected]>
To: "Linux-8086" <[email protected]>
Sent: Friday, March 24, 2006 12:28 AM
Subject: Re: BCC, ELKS 24 Bit addressing mode
Quoted 11 lines
True, I undesrstand, I just thought that the extra banking logic needed and the software overhead might negate that added integration, but I'm not sure what your goal is in the project. I've got some 186 CPUs sitting around if you have any need for a couple.
Dan
Quoted 1 line · Jody
186 CPUs have various non-CPU functionality integrated into the chip
itself,
Quoted 4 lines
Quoted 4 lines
which is one reason it's popular in some embedded designs.
Quoted 1 line · Dan Olson
Quoted 1 line
Quoted 1 line
Basically you're working with a 286 that's been lobotmized down to a
186
Quoted 7 lines
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Quoted 7 lines
Quoted 5 lines
Quoted 3 lines
with the addressing features in place?
yes, but I need to address 16 Mbytes of RAM so I need to use 24 bit addressing mode.
Quoted 8 lines
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Quoted 8 lines
I hate to ask, but why bother with a 186 in the first place? As I understand it, the only real difference (other than some hardware integration) between the two is that the 286 has a 24 bit address space....which you'd need if you're going to use 16M of RAM anyway.
Dan
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in
Quoted 12 lines
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the body of a message to [email protected]
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Quoted 3 lines · Dan Olson
I hate to ask, but why bother with a 186 in the first place? As I understand it, the only real difference (other than some hardware integration) between the two is that the 286 has a 24 bit address space....which you'd need if you're going to use 16M of RAM anyway.
Dan
That was something I was thinking about after that post. I wonder what the benefits to have addressing mode even more constrained than found in 286 and still bother with those crappy 64kb segments? Is that hardware really cheap or wide spread around?
Anyway, it looks like you may add this addressing mode handling to EXE image loader that would change all cross-segment access addresses to be compatible with this addressing mode. You may want to try it under plain DOS. Btw, seems this way you still keep all EXE compatible with 8088.
Andrey
So basically, you've got segmentation in 256-byte increments instead of 16 in order to handle an additional four address lines, correct?
That sounds like something that shouldn't be difficult to change, but I know nothing about how to do it.
Jody
Quoted 22 lines · Serdar Sutay
Dear All,
I am porting ELKS to a special version of 80186 to be used in embedded devices. This special version known as Turbo186 is using 24 bit addressing using a special addressing scheme. So I need to modify bcc or as86 to support 24 bit addressing mode.
This type of operation is common in embedded usage. 24 bit addressing is working like this,
In normal 20 bit addressing when far jumps are used, two 16 bit operands are given for address calculation. First operand is left shifted 4 bits and added to second operand, then 20 bit address is calculated.
In 24 bit addressing mode, first operand is left shifted 8 bits and added to second operand, resulting in 24 bit address.
What am I required to do to support 24 bits addressing in bcc? Can you give me some insight or guide me to the correct person?
Thank you for your consideration and help.
Kindest regards,
Serdar Sutay
-
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More majordomo info at http://vger.kernel.org/majordomo-info.html
Hi,
I cannot help you unfortunately But please let me know what happens I am really interested!
Thanks,
Eric des Courtis
Quoted 44 lines · Jody
So basically, you've got segmentation in 256-byte increments instead of 16 in order to handle an additional four address lines, correct?
That sounds like something that shouldn't be difficult to change, but I know nothing about how to do it.
Jody
Quoted 22 lines · Serdar Sutay
Dear All,
I am porting ELKS to a special version of 80186 to be used in embedded devices. This special version known as Turbo186 is using 24 bit addressing using a special addressing scheme. So I need to modify bcc or as86 to support 24 bit addressing mode.
This type of operation is common in embedded usage. 24 bit addressing is working like this,
In normal 20 bit addressing when far jumps are used, two 16 bit operands are given for address calculation. First operand is left shifted 4 bits and added to second operand, then 20 bit address is calculated.
In 24 bit addressing mode, first operand is left shifted 8 bits and added to second operand, resulting in 24 bit address.
What am I required to do to support 24 bits addressing in bcc? Can you give me some insight or guide me to the correct person?
Thank you for your consideration and help.
Quoted 8 lines
Kindest regards,
Serdar Sutay
-
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Serdar Sutay wrote:
[...]
Quoted 2 lines
What am I required to do to support 24 bits addressing in bcc? Can you give me some insight or guide me to the correct person?
AFAIK, bcc knows nothing about segmentation --- it deals strictly with 16-bit code. Which means that nothing will need changing. If the Turbo186 uses all the same opcodes as a normal 186, you wouldn't even need to modify as86.
What *will* need modification is the kernel code that allocates segments and sets up the segment registers for the user processes, and unfortunately I don't know anything about how that works. It's entirely feasible that all you would need to do is to change a few small chunks of assembly.
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