Writing PCR-file for use with wpcredit.exe
Posted: Wed Nov 22, 2006 4:32 pm
I spent the last two days writing a .pcr file for the SiS 530 chipset, to be precise for the SiS "Host to PCI bridge" - device within that chipset.
It was my first approach to dig into this field but since I spent years on programming (long time ago) it was not that much of a problem.
as a starting point I used a pcr-file that was already in production but not finished - thank you stedman5040 for sending me a copy of your work!
I don't want to give here a lecture on how to write a pcr-file but I just want to share some information with all those who did not dare yet to start with but would like to do so.
for beginners: grab (google for) the specific chipset documentation you need. then try to locate "any" .pcr file even it is not for your chipset. just open it and "study" the way it is written. every .pcr-file looks the same and has the same structure. it is just the register-addresses and values (the bits within) and the explaining words YOU have to match to the chipset (device) of your liking.
1. if the chipset spec-documentation says that bit# x within a register is RO (read only) then use "(" ")" to let wpcredit display it colored accordingly.
for example if your spec-doc says that register 84h, bit 7 is RO it tells whether l2-cache is installed or not you would write the line:
(84:7)=L2 cache exists 1=yes 0=no
wpcredit then would use a different color to show this bit as RO. trying to set a RO-bit via wpcredit would not accomplish anything and does not hurt the system (it automatically blocks write access).
2. if register-bit(s) are meant to be RW (read/write) then you would write the line, for example:
[83:6]=L2-cache, 1=Enable 0=disable
the difference here that I want to draw your attention to is that for RW registers/bits you use the "[" "]".
3. a "register" is an address within the memory. it gets its distinctive name by calling it accordingly to the address it is stored within the register memory block. it is not necessary to know where in the memory the registers' are stored. they start at an address known to the system and the very first register gets its distinctive denomination by adding a counter starting from 0, e.g. register 00h, register 01h, ......
the trickier part of writing a pcr-file is the understanding of bit/byte/word/dword values and their representation in a computers memory but also their possible notations as decimal, octal (not of importance here), hexadecimal (suffix h) and binary. here I will not explain how to transcode a value from one notation into another but I will just give you the tip to use the program "calc.exe" that comes along with all windows flavours. just change the program's display and properties from standard to scientific and you get the means for one-click conversions.
for those of you who are not familiar with bits n bytes please note that a byte's 0/1 textual representation starts with bit 7 down to bit 0. BUT the "first" bit of a byte is the "zero"-bit at the 8th textual position (read from left to right):
7 6 5 4 3 2 1 0
so far so easy but the tricky part is already looming. first, what are you going to do when the chipset's spec-sheet says for example: register 58h, graphic window address table, default value 1234h? what is different here is that the value 1234h does not fit into an 8bit register. (for absolute beginners: a byte can handle values from 0 (=00h) up to 255 (=FFh)). logic says that the graphic windows address table needs 2 bytes space. in our case here that means we use register 58h (start register) AND the following register 59h. so we have here a word-value, consisting of a high-byte and a low-byte (2x8bit, bit # (- position) accordingingly:
high-byte............................low-byte
15-14-13-12-11-10-9-8...7-6-5-4-3-2-1-0
at this point it is vitally important to know that a "double-byte" = "word" in a computers memory is stored in "reverse order" compared to the string value "1234h" writtten here in plain text format. when I write 1234h, then the "high" byte value "12h" comes first, followed by the lower byte value "34h". but a computers memory space stores the lower byte value "34" first at a given address and then (in consecutive memory, i.e. higher memory address) the high byte's value "12". to sum it up: "34h" is the default value in register 58h (the starting register address, "12h" belongs to register 59h.
you can actually watch this "byte"/"word" behaviour when you start wpcredit and then change the display of the registers from 8 to 16 bit. you will notice that by switching from 8 to 16bit display mode that two consecutive bytes exchange places.
so when the techpaper says register 58, bit 14..11, then you now should know now that this belongs to register address 59h, because bits 14..11 belong to the high byte. since wpcredit uses byte-notation bits 14..11 must be translated into the bit-location of the single byte they belong to. this gives (in accordance with what I have layed-out above) position 6..3, high byte:
[59:6..3]= ....
last but not least the brain teaser: when the spec-sheet tells you of register 58, bits 10..4 then you have to split this info in 2 lines in your pcr-file:
[59:2..0]=blabla
[58:7..4]=blabla
since I stumbled over these somehow tricky situations several times I helped myself by constructing a blueprint. I hope this will make your life easier too.
It was my first approach to dig into this field but since I spent years on programming (long time ago) it was not that much of a problem.
as a starting point I used a pcr-file that was already in production but not finished - thank you stedman5040 for sending me a copy of your work!
I don't want to give here a lecture on how to write a pcr-file but I just want to share some information with all those who did not dare yet to start with but would like to do so.
for beginners: grab (google for) the specific chipset documentation you need. then try to locate "any" .pcr file even it is not for your chipset. just open it and "study" the way it is written. every .pcr-file looks the same and has the same structure. it is just the register-addresses and values (the bits within) and the explaining words YOU have to match to the chipset (device) of your liking.
1. if the chipset spec-documentation says that bit# x within a register is RO (read only) then use "(" ")" to let wpcredit display it colored accordingly.
for example if your spec-doc says that register 84h, bit 7 is RO it tells whether l2-cache is installed or not you would write the line:
(84:7)=L2 cache exists 1=yes 0=no
wpcredit then would use a different color to show this bit as RO. trying to set a RO-bit via wpcredit would not accomplish anything and does not hurt the system (it automatically blocks write access).
2. if register-bit(s) are meant to be RW (read/write) then you would write the line, for example:
[83:6]=L2-cache, 1=Enable 0=disable
the difference here that I want to draw your attention to is that for RW registers/bits you use the "[" "]".
3. a "register" is an address within the memory. it gets its distinctive name by calling it accordingly to the address it is stored within the register memory block. it is not necessary to know where in the memory the registers' are stored. they start at an address known to the system and the very first register gets its distinctive denomination by adding a counter starting from 0, e.g. register 00h, register 01h, ......
the trickier part of writing a pcr-file is the understanding of bit/byte/word/dword values and their representation in a computers memory but also their possible notations as decimal, octal (not of importance here), hexadecimal (suffix h) and binary. here I will not explain how to transcode a value from one notation into another but I will just give you the tip to use the program "calc.exe" that comes along with all windows flavours. just change the program's display and properties from standard to scientific and you get the means for one-click conversions.
for those of you who are not familiar with bits n bytes please note that a byte's 0/1 textual representation starts with bit 7 down to bit 0. BUT the "first" bit of a byte is the "zero"-bit at the 8th textual position (read from left to right):
7 6 5 4 3 2 1 0
so far so easy but the tricky part is already looming. first, what are you going to do when the chipset's spec-sheet says for example: register 58h, graphic window address table, default value 1234h? what is different here is that the value 1234h does not fit into an 8bit register. (for absolute beginners: a byte can handle values from 0 (=00h) up to 255 (=FFh)). logic says that the graphic windows address table needs 2 bytes space. in our case here that means we use register 58h (start register) AND the following register 59h. so we have here a word-value, consisting of a high-byte and a low-byte (2x8bit, bit # (- position) accordingingly:
high-byte............................low-byte
15-14-13-12-11-10-9-8...7-6-5-4-3-2-1-0
at this point it is vitally important to know that a "double-byte" = "word" in a computers memory is stored in "reverse order" compared to the string value "1234h" writtten here in plain text format. when I write 1234h, then the "high" byte value "12h" comes first, followed by the lower byte value "34h". but a computers memory space stores the lower byte value "34" first at a given address and then (in consecutive memory, i.e. higher memory address) the high byte's value "12". to sum it up: "34h" is the default value in register 58h (the starting register address, "12h" belongs to register 59h.
you can actually watch this "byte"/"word" behaviour when you start wpcredit and then change the display of the registers from 8 to 16 bit. you will notice that by switching from 8 to 16bit display mode that two consecutive bytes exchange places.
so when the techpaper says register 58, bit 14..11, then you now should know now that this belongs to register address 59h, because bits 14..11 belong to the high byte. since wpcredit uses byte-notation bits 14..11 must be translated into the bit-location of the single byte they belong to. this gives (in accordance with what I have layed-out above) position 6..3, high byte:
[59:6..3]= ....
last but not least the brain teaser: when the spec-sheet tells you of register 58, bits 10..4 then you have to split this info in 2 lines in your pcr-file:
[59:2..0]=blabla
[58:7..4]=blabla
since I stumbled over these somehow tricky situations several times I helped myself by constructing a blueprint. I hope this will make your life easier too.
