Re: [real coding] DOS2 and Memory...
Hi people, Thinking that you should set the interruptvector at #C000 when you set I to #C0 is a commonly made mistake in the MSX world. You should set your interruptpointer at address #C0FF instead. As some of you might know, the databus in the MSX is connected to VCC with pull-up resistors. As a consequence the Z80 will always fetch the value 0xFF when reading from the databus at a moment that no device is writing to the databus. For example, when the Z80 reads the databus in IM2 after having received an interrupt request. Well as I wrote I always filled in the whole area from #C000 to #CFFF so I never got problems with it (nowadays I program under Dos environment so I don't use it anymore). By the way, that will be C0FE and not C0FF, because interrupt-vectors can only be even numbers, bit 0 is ignored (always zero). Recently, I read the specs of of my Philips modem adapted to an RS232... The chip inside can generate an interrupt-vector... Is this put through to the MSX, will it really generate a vector when used in IM2??? If so, that would be cool. Or is the MSX standard not capable to use a IM2-vector? ~Grauw MSX Mailinglist. To unsubscribe, send an email to [EMAIL PROTECTED] and put in the body (not subject) "unsubscribe msx [EMAIL PROTECTED]" (without the quotes :-) Problems? contact [EMAIL PROTECTED] (www.stack.nl/~wiebe/mailinglist/)
Re: [real coding] DOS2 and Memory...
On Mon, 22 Feb 1999, Alex Wulms wrote: Thinking that you should set the interruptvector at #C000 when you set I to #C0 is a commonly made mistake in the MSX world. You should set your interruptpointer at address #C0FF instead. As some of you might know, the databus in the MSX is connected to VCC with pull-up resistors. As a consequence the Z80 will always fetch the value 0xFF when reading from the databus at a moment that no device is writing to the databus. For example, when the Z80 reads the databus in IM2 after having received an interrupt request. This is true on a standard MSX with correct devices connected to it. If on the other hand a device only checks IORQ and not M1, it might put data on the bus when it is read at interrupt-time (In this mode IORQ and M1 are both active). Conclusion: Putting the interrupt vector on [I]fe (I believe the last bit is set to 0, since a 2-byte address is fetched) should be enough on a corruct machine, but it is more secure to fill the whole table from [I]0 to [I]fe, so: jumptable: equ hc000 ld a,.high. jumptable ld i,a ld hl,interrupt_routine ld (jumptable),hl ;fill table up ld hl,jumptable ld de,jumptable+2 ld bc,Hfe ldir Bye, shevek --- Visit the internet summercamp via http://polypc47.chem.rug.nl:5002 MSX Mailinglist. To unsubscribe, send an email to [EMAIL PROTECTED] and put in the body (not subject) "unsubscribe msx [EMAIL PROTECTED]" (without the quotes :-) Problems? contact [EMAIL PROTECTED] (www.stack.nl/~wiebe/mailinglist/)
Re: [real coding] DOS2 and Memory...
] This is true on a standard MSX with correct devices connected to it. If on ] the other hand a device only checks IORQ and not M1, it might put data on ] the bus when it is read at interrupt-time (In this mode IORQ and M1 are ] both active). A device which ignores M1 does not respect the Z80 nor the MSX bus protocol, hence is not MSX compatible! Such a device will not only cause problems in IM2 but also in IM0 (the Z80 expects to get an instruction, in the MSX it will always be 0xFF which is RST 38h) and even in IM1 such a device may cause problems. In the last case because a device may generate wait-states. Especially when it is slow. This might impact the timing of games, copyprotections and other softwares that rely on accurate timing. And ofcourse it might also impact the functionality of the device itself. Some devices reset/set some internal bits after they have been read or think that they have been read. For example, the VDP resets the interrupt request bit after its status port has been read and it increases the address counter after its dataport has been read. Ofcoure, the I/O decoding for the VDP does respect the MSX bus protocol so we have never had any problems with that. Anyway, as far as I'm concerned you should ban devices from your MSX that are not MSX compatible. ] ] Conclusion: Putting the interrupt vector on [I]fe (I believe the ] last bit is set to 0, since a 2-byte address is fetched) should be enough The last bit is not set to 0 but read from the databus. Just like the other 7 bits. If you store the interrupt vector at the even address, your program will NOT work. Just try it. In a system that really supports IM2, you can have a convention that the device will only set the highest 7 bits and that the lowest bit musts always be set to 0. You can even enforce this with a specially designed circuit. But as far as the Z80 is concerned: it really reads all bits that are placed on the databus. In the case that an incompatible device would place an arbitrary number on the bus -which can be both an odd and an even number- there is only one real good solution: make sure that the high byte and the low byte of the interruptroutine are the same. For example: jumptable: equ hc000 interrupt_routine: equ h8080 ld a,.high. jumptable ld i,a ;initialize table ld hl,jumptable ld (hl),.low. interrupt_routine ;fill table up (from c000 upto and including c100) ld de,jumptable+1 ld bc,H100 ldir org interrupt_routine ; the real interruptroutine But as I already mentioned, you should ban such a device from your MSX anyway. And when using only compatible devices, my original routine is sufficient (store the pointer only at ofset 0xff in the table). Kind regards, Alex Wulms -- Alex Wulms/XelaSoft - MSX of anders NIX - Linux 4 ever See my homepage for info on the *** XSA *** format http://www.inter.nl.net/users/A.P.Wulms MSX Mailinglist. To unsubscribe, send an email to [EMAIL PROTECTED] and put in the body (not subject) "unsubscribe msx [EMAIL PROTECTED]" (without the quotes :-) Problems? contact [EMAIL PROTECTED] (www.stack.nl/~wiebe/mailinglist/)
Re: [real coding] DOS2 and Memory...
At 10:13 PM 2/22/99 +0100, you wrote: [about using IM2] You should set your interruptpointer at address #C0FF instead. As some of you might know, the databus in the MSX is connected to VCC with pull-up resistors. As a consequence the Z80 will always fetch the value 0xFF when reading from the databus at a moment that no device is writing to the databus. For example, when the Z80 reads the databus in IM2 after having received an interrupt request. Years ago, one of the NOP programmers told me that some devices do write a value to the databus during an interrupt. To make sure your program will work in any configuration, you need to fill 257 bytes with the same value. For example #81 for a routine at #8181. Bye, Maarten MSX Mailinglist. To unsubscribe, send an email to [EMAIL PROTECTED] and put in the body (not subject) "unsubscribe msx [EMAIL PROTECTED]" (without the quotes :-) Problems? contact [EMAIL PROTECTED] (www.stack.nl/~wiebe/mailinglist/)
Re: [real coding] DOS2 and Memory...
] You probably won't get problems. ] However, in Dos it is easiest to replace the bytes at adress #38, for ] example putting a JP Interrupt there. In Basic, it is -to my opinion- better ] if you swith away the ROM, however you could also set the other interrupt ] mode (mode 2?) in which the high byte of the adress of a jumptable is set in ] the I-register and the low byte of the adress is determined by the devie. ] For example, set I to #C0, and then fill adresses #C000-#C0FF with words of ] the adress the interrupt should jump to (yes, indeed, the device can only ] set odd adresses) (there are no devices delivering this lower byte of the ] adress on the MSX. So #C000 can be assumed as the set adress. However, it is ] still safe to fill the omplete 128 words with the right value, just in ] case...) Hi people, Thinking that you should set the interruptvector at #C000 when you set I to #C0 is a commonly made mistake in the MSX world. You should set your interruptpointer at address #C0FF instead. As some of you might know, the databus in the MSX is connected to VCC with pull-up resistors. As a consequence the Z80 will always fetch the value 0xFF when reading from the databus at a moment that no device is writing to the databus. For example, when the Z80 reads the databus in IM2 after having received an interrupt request. This is for example a codefragment, which I used in the 'No Waste' demo: intvector: equ #88ff ; int. vector int mode 2 scroll: di im 2 ld a,.high. intvector ld i,a ; Startoffset for int table ld hl,vertint ld (intvector),hl ; Set interruptvector ei ret vertint:in a,(#99) ; some code cut-out ei reti Kind regards, Alex Wulms -- Alex Wulms/XelaSoft - MSX of anders NIX - Linux 4 ever See my homepage for info on the *** XSA *** format http://www.inter.nl.net/users/A.P.Wulms MSX Mailinglist. To unsubscribe, send an email to [EMAIL PROTECTED] and put in the body (not subject) "unsubscribe msx [EMAIL PROTECTED]" (without the quotes :-) Problems? contact [EMAIL PROTECTED] (www.stack.nl/~wiebe/mailinglist/)
Re: [real coding] DOS2 and Memory...
I read (nearly) all the messages from the last time... - Oh my god! I really miss mails refering to (program-) technical thingies... So - lets start a "serious" thread... ;cP **Great** DOS 2 memory -- I found out that the DOS2 page-switch routines are kinda slow. Does anybody know a simple, "legal", and compatible way to speed up those bottlenecks? Compatible, because I dunno how many different versions of DOS2 are in use. - And I want it to work with every kind of DOS2. The segment number Dos2 returns is the same as the MemMap page-number. Therefor, you can use the number you get if you allocate a page with OUT (#FC-#FF). It is illegal (ofcourse), but it works. This way you an also switch away page 3. But beware: If you set pages this way and you want to read from disk to that page the Bdos sets the old page he's got in his table. Really, these routines are made as fast as possible, so don't worry about speed. And if you do use the thing stated above, take care... Oh - another question comes in mind: In DOS1 you are not allowed to "ask" the outs (#fe...) about the page number which they may contain. You can't. Just use the pages starting with 0. So if you need 96k then use pages 0-5... - How will I know which ones are selected? - Is there a _STANDARD_ definition which memmaps are selected after the bootstrap? In dos1, the following table is valid: -3FFF: page 3 4000-7FFF: page 2 8000-BFFF: page 1 C000-: page 0 In Dos2 you should request the segment-nrs. using Get_Seg. DOS2 and Interrupts: I want to redirect the standard-interrupt (with use of IMx). Will I get troubles if there is NO(!) ROM selected in page0/1 the whole time? - I dont wanna load in this situation, only wanna switch mem... You probably won't get problems. However, in Dos it is easiest to replace the bytes at adress #38, for example putting a JP Interrupt there. In Basic, it is -to my opinion- better if you swith away the ROM, however you could also set the other interrupt mode (mode 2?) in which the high byte of the adress of a jumptable is set in the I-register and the low byte of the adress is determined by the devie. For example, set I to #C0, and then fill adresses #C000-#C0FF with words of the adress the interrupt should jump to (yes, indeed, the device can only set odd adresses) (there are no devices delivering this lower byte of the adress on the MSX. So #C000 can be assumed as the set adress. However, it is still safe to fill the omplete 128 words with the right value, just in case...) MSX Mailinglist. To unsubscribe, send an email to [EMAIL PROTECTED] and put in the body (not subject) "unsubscribe msx [EMAIL PROTECTED]" (without the quotes :-) Problems? contact [EMAIL PROTECTED] (www.stack.nl/~wiebe/mailinglist/)
[real coding] DOS2 and Memory...
Hi! I read (nearly) all the messages from the last time... - Oh my god! I really miss mails refering to (program-) technical thingies... So - lets start a "serious" thread... ;cP DOS 2 memory -- I found out that the DOS2 page-switch routines are kinda slow. Does anybody know a simple, "legal", and compatible way to speed up those bottlenecks? Compatible, because I dunno how many different versions of DOS2 are in use. - And I want it to work with every kind of DOS2. Oh - another question comes in mind: In DOS1 you are not allowed to "ask" the outs (#fe...) about the page number which they may contain. - How will I know which ones are selected? - Is there a _STANDARD_ definition which memmaps are selected after the bootstrap? DOS2 and Interrupts: I want to redirect the standard-interrupt (with use of IMx). Will I get troubles if there is NO(!) ROM selected in page0/1 the whole time? - I dont wanna load in this situation, only wanna switch mem... hope to get interesting answers... greetz JJoS (or call me chief-gavaman) MSX Mailinglist. To unsubscribe, send an email to [EMAIL PROTECTED] and put in the body (not subject) "unsubscribe msx [EMAIL PROTECTED]" (without the quotes :-) Problems? contact [EMAIL PROTECTED] (www.stack.nl/~wiebe/mailinglist/)
