Method and apparatus for reset-sensitive and controlled register write accesses in a data processing system with user and test modes
First Claim
1. A method for operating a data processor, said method comprising the steps of:
- performing a first write access to a first control bit, the first write access being an initial write access after a reset of the data processor, wherein the first control bit is for configuring at least one parameter of the data processor;
causing the first write access to the first control bit to have no effect on the first control bit;
performing a second write access to the first control bit, wherein the second write access is subsequent to the first write access;
causing the second write access to the first control bit to affect the first control bit;
performing a third write access to the first control bit, wherein the third write access is subsequent to the second write access; and
causing the third write access to the first control bit to affect the first control bit.
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Accused Products
Abstract
A method for accessing a control register in a data processing system which ignores a first write to sensitive control bits when in a first mode, but allows subsequent writes to the sensitive control bits. When operating in a user mode, the method allows a first write to the sensitive control bits, but does not allow any subsequent writes. When a write access is made to the sensitive control bits during test mode only non-initial writes are effective. When a write access is made to the sensitive control bits during user mode only an initial write is effective. The method is effective in a data processing system having a control register write access scheme.
42 Citations
19 Claims
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1. A method for operating a data processor, said method comprising the steps of:
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performing a first write access to a first control bit, the first write access being an initial write access after a reset of the data processor, wherein the first control bit is for configuring at least one parameter of the data processor; causing the first write access to the first control bit to have no effect on the first control bit; performing a second write access to the first control bit, wherein the second write access is subsequent to the first write access; causing the second write access to the first control bit to affect the first control bit; performing a third write access to the first control bit, wherein the third write access is subsequent to the second write access; and
causing the third write access to the first control bit to affect the first control bit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An integrated circuit, said integrated circuit comprising:
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a register; and control circuitry coupled to the register for determining if a present write access to the register is a first write access after reset; wherein if the present write access to the register is the first write access to the register after reset, said control circuitry will cause the present write access to the register to have no effect on the register; and wherein if the present write access to the register is not the first write access to the register after reset, said control circuitry will cause the present write access to the register to affect the register by writing to the register. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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17. A method for operating a data processor, said method comprising the steps of:
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resetting the data processor, wherein a control register for configuring the data processor is enabled; performing a first write access to a first control bit in the control register, the first write access being an initial write access after reset while the control register is enabled; causing the first write access to the first control bit to have no effect on the first control bit; performing a second write access to the first control bit, wherein the second write access is subsequent to the first write access while the control register is enabled; and causing the second write access to the first control bit to affect the first control bit. - View Dependent Claims (18, 19)
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Specification