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US4766537A
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Paged memory management unit having stack change control register
Assignee: NXP USA Inc
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Filing: 1986-01-02
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Granted: 1988-08-23
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Expires: 2006-01-02
Abstract
Abstract A paged memory management unit (PMMU) adapted to prevent unauthorized access by a calling module executing in a data processor to a called module having a higher access level. A Stack Change Control Register in the PMMU has a bit corresponding to each valid access level. If the PMMU determines that any bit in the Stack Change Control Register corresponding to an access level between the access level of the calling module and the called module, including the access level of the called module, is set, a Change Stack bit in a Status Register is set to indicate that the processor should allocate a new stack for the called module. Both the Stack Change Control Register and the Status Register are accessible to the processor.
Inventors
- 👤 John Zolnowsky
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 13:12
CPC Classifications
G; G06; G06F; G06F12/00; G06F12/14; G06F12/1458; G06F12/1491; G06F12/02; G06F12/08; G06F12/10; G06F12/1027; G06F12/1045; G06F12/1063
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
147 words
In a paged memory management unit (PMMU) which cooperates with a processor to provide access by a calling module to called module, each of said modules having a selected one of a plurality of access levels and being allocated a new stack area by the processor in response to the processor receiving a change stack signal, the improvement comprising: storage means for selectively storing a stack change indicator for each of said access levels, each of said indicators being selectively set in response to a respective signal from said processor; and control means, responsive to said storage means, for providing said change stack signal to said processor if any stack change indicator in said storage means corresponding to an access level between the access level of the calling module and the access level of the called module, including the access level of the called module, is set.
Claim 2
Dependent Claim
147 words
In a paged memory management unit (PMMU) which cooperates with a processor to provide access by a calling module to called module, each of said modules having a selected one of a plurality of access levels and being allocated a new stack area by the processor in response to the processor receiving a change stack signal, the improvement comprising: storage means for selectively storing a stack change indicator for each of said access levels, each of said indicators being selectively set in response to a respective signal from said processor; and control means, responsive to said storage means, for providing said change stack signal to said processor if any stack change indicator in said storage means corresponding to an access level between the access level of the calling module and the access level of the called module, including the access level of the called module, is set.
Claim 3
Dependent Claim
34 words
The PMMU of claim 1, wherein the improvement further comprises: a status register accessible to said processor; and wherein said control means provide said change stack signal to said processor via said status register.
Claim 4
Dependent Claim
16 words
In the PMMU of claim 2, the further improvement wherein the storage means comrpise a register.
Claim 5
Dependent Claim
39 words
In the PMMU of claim 1, the further improvement wherein said control means provides said change stack signal only if the access level of the called module is greater in privilege than the access level of the calling module.
Claim 6
Dependent Claim
16 words
In the PMMU of claim 4, the further improvement wherein the storage means comprise a register.
Claim 7
Dependent Claim
34 words
The PMMU of claim 4, wherein the improvement further comprises: a status register accessible to said processor; and wherein said control means provide said change stack signal to said processor via said status register.
Claim 8
Dependent Claim
16 words
In the PMMU of claim 6, the further improvement wherein the storage means comprise a register.
Claim 9
Dependent Claim
140 words
In a paged memory management unit (PMMU) which cooperates with a processor to provide access by a calling module to a called module, each of said modules having a selected one of a plurality of access levels and being allocated a new stack area by the processor in response to the processor receiving a change stack signal, the method comprising the steps of: selecting storing a stack change indicator for each of said access levels, each of said indicators being selectively set in response to a respective signal from said processor; and providing said change stack signal to said processor if any stack change indicator in said storage means corresponding to an access level between the access level of the calling module and the access level of the called module, including the access level of the called module, is set.
Claim 10
Dependent Claim
140 words
In a paged memory management unit (PMMU) which cooperates with a processor to provide access by a calling module to a called module, each of said modules having a selected one of a plurality of access levels and being allocated a new stack area by the processor in response to the processor receiving a change stack signal, the method comprising the steps of: selecting storing a stack change indicator for each of said access levels, each of said indicators being selectively set in response to a respective signal from said processor; and providing said change stack signal to said processor if any stack change indicator in said storage means corresponding to an access level between the access level of the calling module and the access level of the called module, including the access level of the called module, is set.
Claim 11
Dependent Claim
24 words
In the PMMU of claim 8, wherein said change stack signal is provided to said processor via a status register acessible to said processor.
Claim 12
Dependent Claim
34 words
In the PMMU of claim 8, wherein said change stack signal is provided only if the access level of the called module is greater in privilege than the access level of the calling module.
Claim 13
Dependent Claim
24 words
In the PMMU of claim 10, wherein said change stack signal is provided to said processor via a status register accessible to said processor.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1991-08-23 | 1992-02-22 | 1992-08-23 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1995-08-23 | 1996-02-22 | 1996-08-23 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1999-08-23 | 2000-02-22 | 2000-08-23 | $7700.00 | Window Closed / Lapsed |