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Diagnostics Made Easy(er) |
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label EX R15,label
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You can use this little trick to debug your assembler programs.
This code will cause a S0C3 Abend. There are two main reasons
for wanting to do this; firstly the registers are left unaltered by the Abend, and secondly this is the only way to get an S0C3
so you can rule out any other statements.
We have included a link to our CRASH macro that will issue this abend.
CRASH Macro |
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Swapping Register Contents |
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CR Rx,Ry
BE *+10
XR Rx,Ry
XR Ry,Rx
XR Rx,Ry
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This little trick can be used to swap the contents of two registers. Its neat in that it uses no additional
storage and because of this it is useful when the size of the program is becoming an issue. In fact this method only uses 12 bytes, but only 6 if you exclude the compare.
The initial compare will prevent the register Rx from being made zero if the contents
of both registers are equal.
We have included a link to our SWAPREG macro that will swap two registers
SWAPREG Macro |
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Perform Once Mechanism |
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SWITCH1 NOP DEST
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. execute once code
. goes in here
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OI SWITCH1+1,X'F0'
switch
DEST DS 0H continue from here
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Sometimes it is necessary to execute a sequence of instructions only once even if the code is called several times.
Although good programming practice is usually to steer well clear of self modifying code, here is a piece of code that alters the branch in the
NOP from 'never' branch to 'always' branch. In this example the NOP at SWITCH1 is flipped from a branch '00' (never
branch) to a branch 'F0' (always branch) so that after the first iteration subsequent runs through the code will
branch round to DEST and not execute the code between the SWITCH1 and DEST. |
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Hexprint Macro |
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L Rx,value
LA Ry,WTO+8(8)
HEXPRINT Rx,Ry
WTO WTO 'RxRxRxRx = Contents'
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This is a HEXPRINT macro. Basically the contents of the first register specified (Rx)
are converted to printable characters and placed at the location whose address is loaded into the second register
(Ry). It can be used several times within the same program. Click the link
below to download the macro. All that we ask is that you leave the Copyright information in it please.
We frequently use this macro for diagnosis and tracing.
HEXPRINT Macro |
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How to make hex code
printable (part 2) |
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LA R0,8
Set loop counter
LA R1,your_out_area Point to
target area
LOOP_it LA R2,X'0F'
Prime R2 with 0F
SLDL R2,4
Shift first nibble from R3
CH R2,=X'00FA'
Is it F0 to F9?
BL SKIP
...No, skip subtract
SH R2,=X'0039'
Subtract 39 to get Hex letter
SKIP STC R2,0(R1)
Store the character into R1
LA R1,1(R1)
Skip up output field
BCT R0,LOOP_it
Loop until done
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This piece of code is pretty useful for
making the hexadecimal value in R3 printable, however it does require
that registers 0-2 get 'destroyed', therefore we urge you to save
the contents of those registers before using this code if the contents of them are important to you.
This code is best used in it's own little subroutine where the registers get saved on entry and restored on
exit. The other advantage of using this code is
that it doesn't require any assembler macros, so it is usable 'out of
the box'.
We have included a link to our PRINTHEX macro that will perform a hex print. It will save all registers and restore them on exit.
PRINTHEX Macro |
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Write to Programmer Macro |
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Label1 WTP 'Test message'
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This simple macro is used in the exact same way as the IBM supplied WTO macro, the only difference
is that the WTP macro will set the routing and descriptor codes so that the message should not appear on the console.
You may need to check with your site system programmer to make sure that they haven't changed
the IBM standards for routing and descriptor codes.'
WTP Macro |
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Folding to Uppercase |
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Label1 OC FIELD,=256C' ' Fold to Uppercase
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This code will fold the contents of FIELD into all upper case characters. If you really don't want to use XL256 then you can simply
replace 256 with the length of FIELD.
We have included a link to our UPPER macro which will generate this code.
UPPER Macro
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Random Number Generator Macro |
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Label1 RANDOM 1,100 Generate random number
* Between 1 and 100
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This simple macro will generate a random number (based of the IBM TIME macro) between the two
numbers specified on the macro call. The number is returned in binary form in general register 0.
To convert the number into printable format you can use our HEXPRINT macro (detailed above).
(Note that both registers 0 and 1 will be trashed by this macro as it uses the TIME macro)
RANDOM Macro |
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Checking for a DDNAME |
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Label1 DEVTYPE =CL8'yourdd ',DEVAREA Look for yourdd DD
LTR 15,15 Did we have one?
BNZ Not_Found No - Go and do something
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DEVAREA DS D For DEVTYPE call
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This sample shows how to check to see if a JCL stream contains a particular DD Card (yourdd).
Obviously 'yourdd' should be replaced with something useful (like SYSIN).
If you want to check for a generic
DD statement then you can always say:
DEVTYPE =CL4'TEST',DEVAREA
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