[comp.sys.mac.hypercard] Can XCMDs change the MMU mode?

kougiour@m.cs.uiuc.edu (11/07/89)

I have written a very simple XCMD for the hypertalk. Its purpose
is to reset a card located in one of the Mac II slots. This
is done very simply by writting a zero into an address located
at the card's address space. The routne is written in MPW C 3.0.
Since I cannot access this address when the MAC II operates in 24 bits
mode I SwapMMUMode() to 32 bits before the operation and then back to 24 bits.

 The routine
works ok as a seperate application but when I used it as an XCMD the
hypercard crashes: "Hypercard quits unexpectedtly (28)". By
commenting part of the code I discovered that the crash happens
somewhwere around the first SwapMMUMode call.

Does anybody has an idea what happens and how I can recover? Thanks