84PCE:Ports:001D - Revision history

Runer112: Cleaned up the first sentence

2016-11-11T00:53:25Z

Cleaned up the first sentence

Runer112: Fix the description to match the note

2016-11-11T00:45:49Z

Fix the description to match the note

Runer112 at 00:39, 11 November 2016

2016-11-11T00:39:23Z

Runer112: Fix privileged PC check description

2016-11-11T00:38:13Z

Fix privileged PC check description

Jacobly at 04:50, 27 August 2016

2016-08-27T04:50:45Z

MateoConLechuga at 19:14, 25 May 2016

2016-05-25T19:14:19Z

Dr. D'nar at 04:19, 24 March 2015

2015-03-24T04:19:14Z

Dr. D'nar: Created page with "001D - ███████ ███████ == Synopsis == '''Port Number:''' 001D-001F '''Functio..."

2015-03-22T01:49:49Z

Created page with "001D - ███████ ███████ == Synopsis == '''Port Number:''' 001D-001F '''Functio..."

New page

[[Category:84PCE:Ports:By_Address|001D - ???????]] [[Category:84PCE:Ports:By_Name|???????]]
== Synopsis ==
'''Port Number:''' 001D-001F

'''Function:''' ???????

This port tells the ???? what ???? the ?????. It therefore controls what ???? can issue ????????????????????????.

@@ Line 5: / Line 5: @@
 '''Function:''' Stores the highest address of privileged executable code
-These ports contain the address of the last byte of privileged code (LSB in 1D, MSB in 1F).
+These ports contain the address (stored little-endian) of the last byte (inclusive) of privileged code.
 The boot code sets this to the end of the boot code (020000), after which the OS sets it to the end of the OS (0AXXXX, varies by OS version).
 Privileged code is allowed to execute port commands (in and out) and read/write to the [[84PCE:Ports:0020|protected memory region]].

@@ Line 5: / Line 5: @@
 '''Function:''' Stores the highest address of privileged executable code
-These ports contain the address of the first byte of unprivileged code (LSB in 1D, MSB in 1F).
+These ports contain the address of the last byte of privileged code (LSB in 1D, MSB in 1F).
-All code before this address is treated as privileged, and all code at and after this address is treated as unprivileged.
 The boot code sets this to the end of the boot code (020000), after which the OS sets it to the end of the OS (0AXXXX, varies by OS version).
 Privileged code is allowed to execute port commands (in and out) and read/write to the [[84PCE:Ports:0020|protected memory region]].

← Older revision		Revision as of 00:39, 11 November 2016
Line 11:		Line 11:
	Unprivileged code always input/read a 0 and get an nmi on output/write.		Unprivileged code always input/read a 0 and get an nmi on output/write.

−	'''Note:''' Determining whether or not an instruction is privileged is performed during the actual execution of the instruction, not during fetching. Due to pipelining, the first byte of the next instruction has (almost always) been ~~fetched~~ by this point, so the PC value checked is 1 byte after the end of the instruction.	+	'''Note:''' Determining whether or not an instruction is privileged is performed during the actual execution of the instruction, not during fetching. Due to pipelining, the first byte of the next instruction has (almost always) been prefetched by this point, so the PC value checked is 1 byte after the end of the instruction.

← Older revision		Revision as of 00:38, 11 November 2016
Line 11:		Line 11:
	Unprivileged code always input/read a 0 and get an nmi on output/write.		Unprivileged code always input/read a 0 and get an nmi on output/write.

−	'''Note:''' ~~when determining~~ whether or not an instruction is privileged, the ~~address ''after''~~ the instruction is ~~used~~.	+	'''Note:''' Determining whether or not an instruction is privileged is performed during the actual execution of the instruction, not during fetching. Due to pipelining, the first byte of the next instruction has (almost always) been fetched by this point, so the PC value checked is 1 byte after the end of the instruction.

← Older revision		Revision as of 04:50, 27 August 2016
Line 5:		Line 5:
	'''Function:''' Stores the highest address of privileged executable code		'''Function:''' Stores the highest address of privileged executable code

−	These ports ~~control which region~~ of ~~memory is allowed to execute port commands~~. It is ~~set~~ to the end of the OS ~~during~~ the ~~boot sequence~~, ~~and~~ is ~~unmapped for what appear~~ to ~~be security reasons~~.	+	These ports contain the address of the first byte of unprivileged code (LSB in 1D, MSB in 1F).
		+	All code before this address is treated as privileged, and all code at and after this address is treated as unprivileged.
		+	The boot code sets this to the end of the boot code (020000), after which the OS sets it to the end of the OS (0AXXXX, varies by OS version).
		+	Privileged code is allowed to execute port commands (in and out) and read/write to the [[84PCE:Ports:0020\|protected memory region]].
		+	Unprivileged code always input/read a 0 and get an nmi on output/write.
		+
		+	'''Note:''' when determining whether or not an instruction is privileged, the address ''after'' the instruction is used.

@@ Line 1: / Line 1: @@
-[[Category:84PCE:Ports:By_Address|001D - &#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;]] [[Category:84PCE:Ports:By_Name|&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;]]
+[[Category:84PCE:Ports:By_Address|001D - Privileged Region]] [[Category:84PCE:Ports:By_Name|Privileged Region]]
 == Synopsis ==
 '''Port Number:''' 001D-001F
-'''Function:''' &#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;
+'''Function:''' Stores the highest address of privileged executable code
-This port tells the &#x2588;&#x2588;&#x2588;&#x2588; what &#x2588;&#x2588;&#x2588;&#x2588; the &#x2588;&#x2588;&#x2588;&#x2588;&#x2588;. It therefore controls what &#x2588;&#x2588;&#x2588;&#x2588; can issue &#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;&#x2588;.
+These ports control which region of memory is allowed to execute port commands. It is set to the end of the OS during the boot sequence, and is unmapped for what appear to be security reasons.