Keil C51 and register banks

"John Eigelaar" schreef in bericht news: snipped-for-privacy@yahoo.co.uk...

It's at least 15 years ago. But as i remember it's a macro inserting registerbankswitching opcode. It's valid until the next time the #pragma macro is passing by.

Default is 0, but the whole processor is switching so all code will be using the new bank. B.t.w. are you sure the 8051 can switch banks, i used it for

Conditional pragma's are not possible as far as i remember. While writing C code you should be sure what bank to use.

Nothing, or switching to 0, look in the spec's of your processor. As said the 8051 maybe has no bankswithing at all :-) I used bankswitching for handling fast interupts: at startup you fill all register banks with needed values, start up the main loop with bank 0, entering the interupt routine the first thing i did was switching to bank 1. This is much faster then exchanging all registers using globals. At the end of the interupt routine i switched back to bank 0 en left. In this way the interupt routines (the 80537 can handle several, with different priorities) has it's own 'virtual' registers.

As said, it's also history for me. I hope you can mange the problem. Goodluck!

Cu Jack

In article , John Eigelaar writes

It's in the manuals. Get An eval CD

/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\ \/\/\/\/\ Chris Hills Staffs England /\/\/\/\/\ /\/\/ snipped-for-privacy@phaedsys.org

Thanx for the response.

As with most things in life nothing is what it seems. My problem turned out to be nothing to do with the compiler but rather a good old timing bug.

Good to know about the bank switching though...

Hallo John,

This pragam tells the compiler which registerbank to use with direct adressing. You can tell the compiler not to use direct adressing of registers at all. You dont need this pragma then (does no harm though) - but it will slow down your code.

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In the code snippet above the MOV instructions are using indirect register adressing. The registerbank ( in this case 0) depends upon the setting of a control register (dont know which one - look it up up in the manual). There is no indirect register version for the PUSH instruction on the 8051. The compiler has to know which bank it is working on to push registers on the stack (notice the AR2 = Absolute Register 2). Workarounds are used when direct register adressing is not enabled.

If your program behaves funny, disable direct register adressing in compiler options (either command line, a pragma or a setting in uVision) and try again.

HTH Markus

The Keil toolchain also allows users to select which register bank they wish to use for ISR's via the 'using' keyword.

Edw> John Eigelaar wrote:

until it sees another one

bank 0

Not sure

The bank will not switch unless you use the "using" Keyword on the interrupt.

This is good not bad. This means the interrupt does not have to push upto 8 registers on to the stack. Note that the registers are actually the internal RAM (bank 0 is the 1st 8 bytes) so each bank you use cost you 8 bytes typical use is bank 0 for normal use and 1 bank for each level on interrupts.

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