dsr_dsrlnkraw.c

// DSR interface code for the TI-99/4A by Tursi
// You can copy this file and use it at will ;)

#include "files.h"
#include "vdp.h"

// uses: scratchpad >8340-8348, >8354, >8355, >8356, >83d0, >83d2, GPLWS

#define DSR_NAME_LEN	*((volatile unsigned int*)0x8354)

unsigned char __attribute__((noinline)) dsrlnkraw(unsigned int vdp) {
	// modified version of the e/a DSRLNK, for data >8 (DSR) only
	// this one does not modify data in low memory expansion so "boot tracking" there may not work.
	unsigned char *buf = (unsigned char*)0x8380;	// 8 bytes of memory for a name buffer (TODO: is this legal? Why did I choose this?)
	unsigned int status = vdp + 1;
	unsigned int ret = 0;  // assume success

	vdp+=9;
	DSR_PAB_POINTER = vdp;

	unsigned char size = vdpreadchar(vdp);
	unsigned char cnt=0;
	while (cnt < 8) {
		buf[cnt] = VDPRD;	// still in the right place after the readchar above got the length
		if (buf[cnt] == '.') {
			break;
		}
		cnt++;
	}
	if ((cnt == 0) || (cnt > 7)) {
		// illegal device name length
		VDP_SET_ADDRESS_WRITE(status);
		VDPWD = DSR_ERR_FILEERROR;
		return 1;
	}
	// save off the device name length (asm below uses it!)
	DSR_LEN_COUNT=cnt;

	unsigned int CRU = 0;
	DSR_NAME_LEN = cnt;
	++cnt;
	DSR_PAB_POINTER += cnt;
	
	// make sure the error byte is zeroed before we start
	vdpchar(vdp+1, 0);

	// TODO: we could rewrite the rest of this in C, just adding support for SBO, SBZ and the actual call which
	// needs to be wrapped with LWPI....
	__asm__(
	"		ai r10,-34				; make stack room to save workspace & zero word\n"
	"		lwpi 0x83e0				; get gplws\n"
	"		li r0,0x8300			; source wp for backup\n"
	"		mov @0x8314,r1			; get r10 for destination\n"
	"bkupl1	mov *r0+,*r1+			; copy register\n"
	"		ci r0,>8322				; test for end of copy\n"
	"		jne bkupl1\n"
	"		jmp begin\n"
	"dsrdat data >aa00\n"
	"begin  clr  r1					; r1=0\n"
	"       li   r12,0x0f00			; cru base to >0f00 (first card -1)\n"
	"       jmp  a2316              ; skip card off.\n"
	"a2310  sbz  0					; card off\n"
	"a2316  ai   r12,0x0100			; next card (>1000 for first)\n"
	"       clr  @0x83d0			; clear cru tracking at >83d0\n"
	"       ci   r12,0x2000			; check if all cards are done\n"
	"       jeq  axxx				; if yes, we didn't find it, so error out\n"
	"       mov  r12,@0x83d0		; save cru base\n"
	"       sbo  0					; card on\n"
	"       li   r2,0x4000			; read card header bytes\n"
	"       cb   *r2,@dsrdat		; >aa = header\n"
	"       jne  a2310				; no: loop back for next card\n"
	"       ai   r2,8            	; offset (contains the data statement, so 8 for a device, for >4008)\n"
	"       jmp  a2340				; always jump into the loop from here\n"
	"a233a  mov  @0x83d2,r2         ; next sub\n"
	"       sbo  0                  ; card on (already is, isn't it??)\n"
	"a2340  mov  *r2,r2             ; grab link pointer to next\n"
	"       jeq  a2310              ; if no pointer, link back to get next card\n"
	"       mov  r2,@0x83d2         ; save link address in >83d2\n"
	"       inct r2					; point to entry address\n"
	"       mov  *r2+,r9            ; save address in r9\n"
	"       movb @0x8355,r5			; get dsr name length (low byte of >8354)\n"
	"       jeq  a2364              ; size=0, so take it \n"
	"       cb   r5,*r2+			; compare length to length in dsr\n"
	"       jne  a233a              ; diff size: loop back for next\n"
	"       srl  r5,8			    ; make length a word count\n"
	"       li   r6,%1              ; name buffer pointer in r6\n"
	"a235c  cb   *r6+,*r2+          ; check name\n"
	"       jne  a233a              ; diff name: loop back for next entry\n"
	"       dec  r5					; count down length\n"
	"       jne  a235c              ; not done yet: next char\n"
	"a2364  inc  r1                 ; if we get here, everything matched, increment # calls\n"
	"       bl   *r9                ; link\n"
	"       jmp  a233a              ; check next entry on the same card -- most dsrs will skip this \n"
	"       sbz  0                  ; card off\n"
	"		li r0,>8300				; load register for restore\n"
	"		mov @0x8314,r1			; get r10 for source\n"
	"rslp1	mov *r1+,*r0+			; copy register\n"
	"		ci r0,>8322\n"
	"		jne rslp1\n"
	"a2388  lwpi 0x8300             ; restore workspace\n"
	"		ai r10,34				; restore stack\n"
	"axxx   seto %0                 ; set error flag\n"
    "       jmp a2388\n"
		: "=r" (ret)
		: "i" (buf)
	);

    // this is a little awkward, but it makes for cleaner asm above
    // will clean it up when we convert the above to C
    if (ret) {
        return 1;
    } else {
        return 0;
    }

}