Plasmo ... sorry to hijack your thread but there's been some interesting discussion for those less familiar with overall architecture.

1. John Coffman has done some work on the assembler for sdcc, but I don't know where that work stands
2. Anders Ostlund has done some work on an assembler for sdcc.
3. The UZI280 libraries for HiTech C coupled with the freeware version, on either the CPU280's CP/M 3 or within UZI280.
4. The PRE280 preassembler distributed with the CPU280 code. Source for this is lost, even by its author. Also usable under CP/M 3 (or the zxcc CP/M emulation subsystem from Windows or Linux).
5. Hector Peraza's Z280 assembler.

I'm still in CP/M 2.2, is there a command to initialize directory like the 'INIT' command in CP/M-68K?

On #2:do you know what licence the editor in the book is under. I was under the impression it was (C) Prentice Hall and had no particular permissions to re-use/redistribute outside of the book ?

Plasmo - Since you have a CPLD and possibly a spare macrocell, you might want to think about a different approach to RAMdisk formatting. In my CPLD I have an I/O accessible flip-flop that is reset at power-on and is set on the trailing edge of a read. The reset signal / pushbutton does not affect it. This flip-flop is read within the cold boot loader and if it's in the reset state the loader sets the entire RAMdisk directory (16K in your case) to E5's using DMA propagation. LDIR would also work. Thus the RAMdisk directory is formatted once and only once at power-on and it's contents remain useable across multiple resets.

Since I don't use USER areas on the RAMdisk, a simple ERA *.* can be used to essentially reformat it if it becomes corrupted during testing and I've never required a power-off/on to accomplish that.

I'm beginning to question Z280's reputation for being buggy.

Quote:

I'm beginning to question Z280's reputation for being buggy.

I'm beginning to wonder myself. I have relied on and deferred to Tilmann Reh's experiences along with information from several users of the Z280, but that information is almost all pre-92, and I've seen datecodes now as late as 97. So I guess it's possible that some bugs actually were fixed, but since the bugs weren't documented neither were the fixes. I've not disassembled the Specialix firmware for their SI/XIO ISA card from the Linux kernel drivers; that might be interesting to see if any of the workarounds were used.

This was what Tilmann Reh said about DIVUW bug:

The DIVUW gives wrong results in certain cases. Such a case is the MSB (bit15) of the divisor being set.

So I tried divide 0x20000000 by 0x8888 and get 0x3c00 quotient and 0x2000 remainder. Try 0x20000000 divide by 0x4888 get 0x70F1 quotient and 0x37F8 remainder. These are the correct answers according to my calculator. I tried three different addressing modes:
divuw[dehl],(addr), divuw[dehl],bc, and divuw[dehl],ix, all give the same answers.

Fritz had got Tilmann's board and has picture of it here: https://www.retrobrewcomputers.org/forum/index.php?t=msg& ;amp ;amp ;th=93&goto=4162&#msg_4162
The date code of Tilmann's Z280 is 8735. The date code of my Z280 that I just did the divuw tests is 9332. So perhaps the divuw bug is fixed since mid 1987.
.

I'm leaning toward porting CP/M because it may test the board more thoroughly and also let me try Hector Peraza (hperaza) Z280 assembler ( https://www.retrobrewcomputers.org/forum/index.php?t=msg& ;amp ;amp ;th=93&goto=3700&#msg_3700). Right now I'm hand assembling the few Z280 extended instructions I needed.

I'm ready to turn on DMA for CF and RAM disk data transfer so I will soon find out whether OUTJMP bug applies to DMA transfer of zero-wait I/O and whether DMA hangs on to the bus for up to 20uS. Any one know what is "Stefan Nitschke Chaos"?

plasmo wrote on Tue, 30 January 2018 06:57

I'm leaning toward porting CP/M because it may test the board more thoroughly and also let me try Hector Peraza (hperaza) Z280 assembler ( https://www.retrobrewcomputers.org/forum/index.php?t=msg& ;amp ;amp ;amp ;th=93&goto=3700&#msg_3700). Right now I'm hand assembling the few Z280 extended instructions I needed.

You can use the Z280 assembler on Unix/Linux with a tool like John Elliott's ZXCC. There is a Windows port available somewhere as well.

The advantage of ZXCC over other CP/M emulators like e.g. z80pack is that with ZXCC you can run any CP/M utility directly from the command line (or from a Makefile), and access files on the host filesystem without having to put everything first in a virtual disk. ZXCC is used, for example, to cross-build CP/M 3 for the CPU280; that's the tool I used as well to develop and test the assembler.

BTW, I love your TinyZ280 board; I just added it to my TODO list . The CPLD is a clever addition that makes it more versatile while keeping the component count down.

FFxxE8 is the refresh controller (section 9.3 of Preliminary technical manual). I don't know what the next three I/O address after FFxxE8 are. Writing zero to FFxxE8 will disable the refresh controller but that will cause my board to crash, but I have not find out why exactly. To turn off the refresh controller, I would clear bit 7 (enable bit), but write non-zero values to remaining 7 bits. Since I do use the refresh counter for the DRAM, it is enabled and programmed to 16uS refresh.

One of the best sources of information on Z80 is Rodnay Zaks' book. Rodnay has given permission for a PDF to be posted online, and you can grab it from the links at the end of this page. For that matter, the whole 'www.z80.info' site is a gold mine, but it needs more Z280, Z380, and eZ80 information. (Z380 and eZ80 are current production, but since both are only available in surface-mount packages, they haven't been as popular with hobbyists)

* CPU may have invalid carry flag when instruction is sandwiched between two EX AF,AF' instructions. That error is also influenced by whether cache is enabled or not.

scf
ex  af,af'
xor a
ex  af,af'

xor a      ;clear sign and carry
ex  af,af'
or  0FFh   ;set sign flag
ex  af,af'