A domain is trapped when a non-zero trap code is introduced. Since this action, by itself, does not set the domain's process-running bit TRUE, an implicit invocation to the domain keeper will not automatically follow the setting the trap code.
Whenever the domain's process-running bit is TRUE and the trap code is non-zero, an implicit invocation (called a trap) of the key in C2 (called the domain keeper key) will occur before the domain takes any other action. Since this is an implicit invocation, the domain keeper key should be a gate key to another domain, called the domain keeper, or the Error Key. The parameters passed are:
Figure 2-14
Byte 0 of the trap code, (called "TC0"), describes the general type of trap. A program event sets bit 4 of TC0 to 1. A program event occurring at the same time as one of the traps described below will cause TC0 values of 8 through 15. A program event occurring alone sets bytes 2 through 5 to zero.
TC0 = 0: A process in the domain encounters one of the program interruption conditions listed below.
Figure 2-15
"Instruction length" is 2, 4, or 6. (The instruction length code cannot be zero.) "Interrupt code" is described in Figure 2-16 below. The operation is completed, suppressed, or terminated, as indicated by the IBM System/370 Principles of Operation.
Figure 2-16
Design note: Since program interrupt code 0 is never generated, the abridged trap code passed to the domain keeper will never be equal to X'80000000', the parameter word for the alleged type convention.
TC0 = 1: A monitor instruction is issued by a domain that specified a 1 bit for the appropriate monitor class in C6 of the domain root.
Figure 2-17
"Mon class" is bits 8 through 15 of the monitor call instruction (the monitor class number). "Monitor code" is the monitor code. (The instruction length is 4.) The instruction execution is completed.
TC0 = 2: Rejected parameter word.
Figure 2-18
TC0 = 3: The domain executed a SVC and LL of the domain's C4 was 00, or LL of C4 was 03 and the SVC code was not 253, 254, or 255.
Figure 2-19
"SVC code" is the interrupt code (right eight bits of the SVC instruction). "Instruction length" is 2 or 4. The instruction execution is completed.
TC0 = 4: The domain encountered an addressing fault at a virtual address for which there was no defined segment keeper key.
Figure 2-20
"Error code" is the error code as summarized in Figure 2-11 entitled "Error Code Summary". "Offending address" is the address that was applied to the domain's addressing segment key. The unit of operation is nullified.
TC0 = 5: The domain attempted an invocation with invalid parameters or depended on an invalid meter.
Figure 2-21
The following two tables (Figures 2-22 and 2-23) describe the meanings of Class code and subcode when TC0 = 5:
Figure 2-22
Figure 2-23
TC0 = 6: The domain attempted an invocation in which the domains involved in the invocation have nodes which overlap in certain unsupported ways.
Figure 2-24
In this discussion, "returnee" refers to that domain designated by the resume key provided as the fourth key parameter of the CALL invocation. The instruction execution is nullified.
Figure 2-25
Design note: This trap code can be prevented by restricting the domain tool key to programs that will not allow overlapping domains to be built.
TC0 = 7: A gate key to the domain was invoked with a string argument, but some required portion of the parameter string was at an address for which the addressing segment provided a read-only page or no page. The invoked domain's instruction execution is suppressed.
Figure 2-26
"Error code" is the error code as summarized in Figure 2-11, "Error Code Summary". "Offending address" is the address that was applied to the domain's addressing segment key.
Programming Note: Between setting the trap code and invoking the domain keeper key, other programs may run.
Programming Note: If the action was an invocation and the fault did not involve the invoking domain, the state of the invoking domain at the conclusion of the invocation will be as if there had been no fault.
Design Note: Normally the setting of the trap code by the kernel replaces DK(0). This is not always the case. Since a domain can take no action other than to trap when the trap code is not zero, these situations occur only when one action causes two trap codes to be produced, or when a trap code is produced when the domain's process-running bit is FALSE. This situation can occur when an invocation is made to a domain with an invalid parameter page key and an entry block that rejects the parameter word. It is implementation dependent which trap code will be stored in these cases.