speccery Posted July 31, 2021 Share Posted July 31, 2021 I have continued to work on my StrangeCart project, which is here in a separate thread. After working quite a bit on the hardware design, firmware design, board validation and so on I'm now working on integrating the StrangeCart with TI Basic, at least a bit. In this process I have had to learn some GPL, but I am definitely a newbie with it. I decided to open a new topic on this, since my GPL adventures and related questions are probably going to be simple in terms of code, and might be of interest (?) to others as well. Even if I am working on this code on my StrangeCart hardware, the GPL code which is not communicating with the StrangeCart should be runnable using Final GROM. Having said that I am not sure if it emulates the 4K SRAM included in the Mini Memory, but that SRAM is not the point of this discussion, normal 32K RAM could be used equally well. Right now my code is not really using RAM outside scratchpad area. My goal is to simply add some new commands to TI Basic, to enable it to interface with the StrangeCart from TI Basic. But before getting that far, I need to develop an understanding how one adds Basic callable routines to a cartridge. I took as the basis of my code the source of the Mini Memory module. It is very interesting for me, as it includes both GPL code and machine code and interfaces between the two. I have now implemented my first GPL routine which can be called from TI Basic, something like CALL LIST(1). My GPL code gets successfully reached and executed, and it manages to get back to Basic gracefully. It decodes one parameter passed by Basic, converts it into an integer, and then passes it over to my assembler routine using the XML GPL opcode. Very conveniently the Mini Memory module implements a XML jump table, and it has one empty unused slot for XML >73. I'm now using that slot for my own machine code. Since GPL debugging is pretty tough, I have resorted to writing to screen memory some characters, to show how my code is advancing. Thierry's tech pages contain the source code for the Mini Memory module. The pages also explain very nicely how the XML tables work, in the GPL section of the website. I ported the source code so that I can use XDT99 (xga99.py and xas99.py) to compile the mini memory module source code with my additions. For those not in the know, the XML >73 is a GPL opcode to branch to a machine code routine. Thus it enables GPL code to call TMS9900 machine code routines. The address where the code branches to is provided in a series of jump tables. The parameter >73 is a hexadecimal value which identifies the jump table to use. It means that the address where to branch to is given in the CPU address >6016. This happens to be in the cartridge ROM space, so it is ideal for my use. I just place into >6016 a pointer to TMS9900 machine code which handles the XML code. The Mini Memory module contains a normal 6K GROM chip. My StrangeCart assumes that all GROMs are actually 8K. This gives me additional 2K of GROM space, where I can easily mock around with my code and add small routines without removing existing Mini Memory code. I have added this GPL routine to handle CALL LIST. I modified the GROM header so that subprogram "LIST" points to the GLIST routine below. The routine decodes the parameter which is passed to it, and writes stuff to screen based on it. If the parameter is zero, it writes the word STRANGE to the screen. If it is non-zero, it writes that value in hexadecimal to the screen at a fixed location. The hexadecimal conversion and writing to screen is done in the assembler code, not in GPL. Spoiler **************************** * Our listing command "CALL LIST" GLIST CALL G@G6530 Skip subprogram name in Basic statement and open parenthesis PARSE >B6 parse next parameter (B6 is closed parenthesis) CEQ >65,@>834C Is it a string? BS G@G6DBE yes: string number mismatch XML >12 no: convert float to integer CEQ >03,@>8354 overflow occured? BS G@G6DB9 yes: issue error ; Now @>834A has our integer. Now we can do something. DCEQ >0000,@>834A Is the integer zero? BS G@DISP_MSG Yes: display our message ; No, just continue. ST >A1,V@>0020 Write something to the screen, we're here! XML >73 Call my assembly routine to display the value in 834A ; >73 returns with Cnd set. B G@G6749 DISP_MSG ; Alright let's show a message from GROM! MOVE >07,G@DSTR1,V*>8320 DADD >0007,@>8320 Advance screen positiong by 7. ST >A2,V@>0020 Write something to the screen, we're here! BR G@G6749 Check current token for ) and return to Basic. DSTR1 DATA >B3B4 'S' & 'T' + 0x60 DATA >B2A1 'R' & 'A' DATA >AEA7 'N' & 'G' DATA >A500 'E',00 The Mini Memory contains 4K of ROM memory in CPU space from >6000..>6FFF. Luckily there is a large chunk of this space which is not used, and I put the XML >73 handler in that space. The routine just writes to screen memory in hexadecimal the value passed from Basic. Spoiler * *--------------------------------------- * Bytes >697E to >6F0D all contain >00 *--------------------------------------- * BSS >0588 *------------------------------------------ * EP: Except in my case I put code in here. * This is where XML >73 lands. * It appears the low registers at least are * safe to change. *------------------------------------------ STRANGECODE ; Test and write the argument from GPL in 834A in hex to the screen. ; Set address MOV 11,@>7004 ; Save return address, probably not needed LI 4,>80 ; Screen address where to write to. LI 1,>8E00 ; '.'+96, write the period character BL @A694E ; Set VDP address, and write byte from R1 MOV @>834A,2 ; Load value to be printed to R2 LI 3,4 ; 4 digits to write. ! MOV 2,1 BL @HEXDIG SLA 2,4 DEC 3 JNE -! B @A6970 Jump to above, get back to GPL HEXDIG ; Write the highest nibble of 1 in hex to VDP memory SRL 1,4 Shift to low nibble of byte CI 1,>0900 Is the value 9 or lower JLE ! Yes: branch AI 1,>0700 No: Add 7 to high byte of R1 ! AI 1,>9000 Add screen offset 60 and 30 to get ASCII of 0 MOVB 1,@>8C00 B *11 BSS >054A A6F06 BSS >0008 * *--------------------------------------- * Default symbol table *--------------------------------------- A6F0E TEXT 'UTLTAB' utility table for loader I have tested this stuff with a Basic program, you can see the listing and output in the pictures below. I could check this, but I wonder what workspace is used to run the XML routine? I assume it is either >8300 or the GPL workspace >83E0, but since the Mini Memory code seems to explicitly restore workspace into >83E0, it is probably at >8300. The other question is, what registers are safe to use in the XML routine machine code? I know I could set up my own workspace, but I like the idea of keeping the workspace in scratchpad memory. Also, what is the "right" way of returning from a XML routine back to Basic? I am currently using the code in the Mini Memory module, at address A6970: A6970 LWPI >83E0 GPL workspace A6974 SOCB @A660D,@>837C set Cnd bit B @>0070 to GPL interpreter 3 Quote Link to comment Share on other sites More sharing options...
speccery Posted July 31, 2021 Author Share Posted July 31, 2021 I just noticed I posted this into the main forum and not into the Development section... Hopefully that's not a problem. Is there a way to move this topic under the Development section? Quote Link to comment Share on other sites More sharing options...
+Lee Stewart Posted July 31, 2021 Share Posted July 31, 2021 1 hour ago, speccery said: Is there a way to move this topic under the Development section? @OLD CS1?? ...lee Quote Link to comment Share on other sites More sharing options...
+OLD CS1 Posted July 31, 2021 Share Posted July 31, 2021 2 hours ago, Lee Stewart said: @OLD CS1?? ...lee 7 Quote Link to comment Share on other sites More sharing options...
HOME AUTOMATION Posted August 1, 2021 Share Posted August 1, 2021 (edited) 8 hours ago, speccery said: I could check this, but I wonder what workspace is used to run the XML routine? I assume it is either >8300 or the GPL workspace >83E0, but since the Mini Memory code seems to explicitly restore workspace into >83E0, it is probably at >8300. The other question is, what registers are safe to use in the XML routine machine code? I know I could set up my own workspace, but I like the idea of keeping the workspace in scratchpad memory. Also, what is the "right" way of returning from a XML routine back to Basic? I am currently using the code in the Mini Memory module, at address A6970: Not entirely sure about BASIC ...but when working with GPL images, I've observed >83E0 to be the GPL interpreters workspace. While executing an XML op-code, >061A BL *R4, uses WORKSPACE >83E0, where R4 holds the jump table's vector address. Thus R11 contains RT address >061C, which in turn jumps to >05E4 B @>0070. I usually try to utilize my own WORKSPACE, than restore GPL WORKSPACE, before using "B *R11" to return to GPL. Pretty sure you're not supposed to alter R13, 14, 15. But I'd bet BASIC might be even more finicky. So, looks like you're doin' AOK! Edited August 1, 2021 by HOME AUTOMATION 2 Quote Link to comment Share on other sites More sharing options...
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