A patch was developed many years ago to cause CP\/M 2 to look on drive A: if it couldn’t find a .COM file. This is probably a precursor to the Windows and MSDOS search PATH command, though unix may have already had a PATH variable.<\/p>\n
You can find a copy of the patch to search drive a at: www.classiccmp.org<\/a>.<\/p>\n BUT it has some side effects. <\/p>\n It worked great for me; until I mistyped a command.<\/p>\n This is what you get normally: <\/code><\/p>\n This is what you get with a mistyped command: <\/code><\/p>\n I have two disks in the system (A: and B:) and the patch tries to access drive C.<\/p>\n Here’s the text of the patch: <\/code> If you look at the code in the CCP that this is patching, you’ll notice that it is changing a drive setting for the CCP; not just for the .COM file we are trying to run. The ‘inr m’ seems to be causing a broader impact (like accessing one more than the current drive – C: when we are on B:).<\/p>\n I found an alternative approach to work better. For a 64K system (cpmb equ 0E400H, CCP at E400-EBFF) it looks like: <\/code> The CCP is the first thing on a bootable disk after the boot sector. On an 8″ SSSD or DSSD system it is in track 0 sector 2 to sector 17 so use a disk editor to patch sectors 15 (EA80-E400=680=13 sectors) and 17. DD sectors are 200H each so if you’re using DD disks, both parts will be in sector 5.<\/p>\n I tend to edit disk images directly, using a hex editor in Windows. You could use GETSYS \/ PUTSYS and DDT\/ZSID within CP\/M to make the same changes.<\/p>\n This is what I get normally: <\/code><\/p>\n This is what I get with a mistyped command: <\/code> This is part of the CP\/M topic<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":" A patch was developed many years ago to cause CP\/M 2 to look on drive A: if it couldn’t find a .COM file. This is probably a precursor to the Windows and MSDOS search PATH command, though unix may have already had a PATH variable. You can find a copy of the patch to search … Continue reading A Better CCPPATCH for CP\/M 2<\/span> <\/p>\n\r\nB>dir\r\nNO FILE\r\nB>stat\r\nA: R\/W, Space: 372k\r\nB: R\/W, Space: 490k\r\n\r\n\r\nB><\/pre>\n
<\/p>\n\r\nB>stap\r\nBdos Err On C: Bad Sector<\/pre>\n
\n<\/p>\n\r\n; This patch causes the CCP of a cp\/m 2.x system to look on drive A\r\n; when you are logged into a drive other than A and call for a .COM\r\n; file that does not exist on that drive. Giving an explicit drive\r\n; reference overrides this feature, so that you can always force\r\n; the file to be loaded from a specific drive.\r\n;\r\nmsize\tequ\t60\t\t; set this to your nominal system size\r\n;\r\ncpmb\tequ\t(msize-20)*1024+3400h\t; start of CCP in given sys size\r\n;\r\n\torg\tcpmb+6dbh\r\n\tjz\tpatch\t\t; replaces \"jz cpmb+76bh\"\r\n;\r\n\torg\tcpmb+7f2h\t; replaces an unused area of NOP's\r\npatch:\r\n\tlxi\th,cpmb+7f0h\t; get drive from current command\r\n\tora\tm\t\t; accum was 0 on entry, so this fetches drive\r\n\tjnz\tcpmb+76bh\t; command has explicit drive...give error\r\n\tinr\tm\t\t; force explicit reference to drive A\r\n\tlxi\td,cpmb+7d6h\t; we need de set up when we\r\n\tjmp\tcpmb+6cdh\t; re-enter ccp\r\n;\r\n\tend\r\n<\/pre>\n
\nThe idea is good: if open fails for the .COM file you jump to a patch area, change the drive specifier from 0 (default) to 1 (drive A), and then redo the process. It has enough smarts to exit if there is already a drive specifier (eg if we typed B:PROG). This also prevents loops if the .COM file isn’t on drive A either (because we now have a drive specifier).<\/p>\n
\n<\/p>\n\r\nEADB: CAF2EB JP Z,EBF2\r\n\r\nEBF2: 1A LD A,(DE)\r\nEBF3: B7 OR A\r\nEBF4: C26BEB JP NZ,EB6B ; to the original error msg\r\nEBF7: 3C INC A ; fcb[0] to 01, ie A:\r\nEBF8: 12 LD (DE),A\r\nEBF9: CDD0E4 CALL E4D0 ; retry the open that failed last time\r\nEBFC: C3DBEA JP EADB ; back to just after last time\r\nEBFF: 00 NOP\r\n<\/pre>\n
\nFor other memory sizes, subtract 4 from the “E4”, “EA” and “EB” values, for each 1K less. This is what the original “cpmb …” line does.<\/p>\n<\/p>\n\r\nB>dir\r\nNO FILE\r\nB>stat\r\nA: R\/W, Space: 372k\r\nB: R\/W, Space: 490k\r\n\r\n\r\nB><\/pre>\n
<\/p>\n\r\nB>stap\r\nSTAP?\r\n\r\nB><\/pre>\n
\nThe difference is I use the FCB address in DE and check and change the drive specifier for the .COM file instead of for the CCP.<\/p>\n