Mechanism to protect data saved on a local register cache during

Details Mechanism to protect data saved on a local register cache during Mechanism to protect data saved on a local register cache during

1994-03-29

1995-09-05

Harrell, Robert B.

Boots, shoes, and leggings

364DIG1, 364DIG2, 3642434, 36424341, 364964, 3649642, 36496427, G06F 1216

Patent

active

054487072

ABSTRACT:
An apparatus for protecting the data in a local register cache during calls and returns that cross subsystem boundaries. The left most bit of a shift register is set to a 1 if a "set boundary bit" instruction is detected. A subsequent PUSH instruction shifts the shift register right one bit. A POPTOS1 instruction in the instruction flow signifies an intra-subsystem return and causes the leftmost bit of the shift register to be checked to see if it is a zero. A protection fault is signalled upon the condition that the leftmost bit is not equal to zero. The shift register is shifted left one bit upon the condition that a POPSTOS 2 instruction is detected. A POPSUB1 instruction detected in the instruction flow signifies an inter-subsystem return and causes the leftmost bit of the shift register to be checked to see if it is a one. A a protection fault is signalled upon the condition that the leftmost bit is not equal to zero. The register is shifted left one bit upon the condition that a POPSTOS 2 instruction is detected in the instruction flow.

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"Modern Electronic Circuits Reference Manual" Markus 1980 p. 540.

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