FPGA project
- Elpekos
This project page describes the hardware specifications of the new FPGA based Z88 platform.
Project status
Full original blink implementation is done and really stable, tested during 3 continuous days without reset.
Platform is actually a common TERASIC DE-1 board with a Cyclone 2 FPGA. Implementation uses the on-board Flash EPROM and SRAM.
Serial port is wired to a FTDI serial-USB adapter. It is fully working and Eazylink, Y-modem transfers are reliable at 38K.
Screen is a VGA monitor, keyboard a standard PS2.
Coma and snooze are implemented, pressing the 2 shifts keys on the PS2 keyboards wakes-up immediately the machine and turns on the VGA monitor.
Improvements
NextZ80 CPU (done)
Working at 6.25MHz. Since this CPU works 4 times faster than the Z80, global speed is 8 times the original Z88.
Zetriz project is compiled in less than 1'30" versus 12' on the real Z88.
Serial port (done)
Full original implementation is done.
The UTEST flag in TXC enables fast baud rates up to 500K baud.
The 31.5K baud speed is possible, allowing a MIDI interface implementation.
SPI controller (done)
Two SPI controller have been implemented in the blink. One is interfaced with the SD card slot.
- SPI layer is implemented
- SD protocol is implemented
- FAT32 is implemented in read-only
- VFAT with long filename support is implemented (allowing OZ full filename length support)
- TODO : SPI layer and SD layer OZ API (W.I.P.)
- TODO : integration in OZ VFS (transparent virtual filesystem already used for eprom file area)
- TODO : write support, erase, format...
SDRAM
The speed will be greatly improved with SDRAM usage. Speed limitation is due to Flash EPROM and SRAM chip latency.
Using a 4M SDRAM will unlock this limitation. A bootstrap has to be implemented in the CPU in order to load OZ in the first 512K before hard reset.
Read-only protection  needs to be implemented in order to protect system.
Dual VGA display
Two VGA output are planned.
OZ could easily support a dual display by switching between two screen base files.
Advanced memory management unit
This feature is intend to protect OZ integrity and avoid lowram corruption. Principles are described below.
Extended Segment register will allow up to 1GByte RAM allocation without loosing compatibility with the actual 4M range.
Blink ports
New blink registers are in bold.
Port | Read | Width | Write | Width | Softcopy |
|---|---|---|---|---|---|
$70 | PB0 | 13 | $0460, $0470 | ||
$71 | PB1 | 10 | $0461, $0471 | ||
$72 | PB2 | 9 | $0462, $0472 | ||
$73 | PB3 | 11 | $0463, $0473 | ||
$74 | SBR | 11 | $0464, $0474 | ||
$75 | SB1 | 8 | $0475 | ||
$76 | SB2 | 8 | $0476 | ||
$77 | SCI | 16 | SCM | 8 | $0477 |
$B0 | MID | 16 | COM | 8 | $04B0 |
$B1 | STA | 8 | INT | 8 | $04B1 |
$B2 | KBD | 8 | MVP | 16 | $04B2 |
$B3 | EPR | 8 | $04B3 | ||
$B4 | TACK | 3 | $04B4 | ||
$B5 | TSTA | 3 | TMK | 3 | $04B5 |
$B6 | ACK | 8 | $04B6 | ||
$B7 | ROM | 8 | $04B7 | ||
$C0 | ES0 | 16 | $04C0, $04D0 | ||
$C1 | ES1 | 16 | $04C1, $04D1 | ||
$C2 | ES2 | 16 | $04C2, $04D2 | ||
$C3 | ES3 | 16 | $04C3, $04D3 | ||
$D0 | TIM0 | 8 | SR0 | 8 | $04D0 |
$D1 | TIM1 | 6 | SR1 | 8 | $04D1 |
$D2 | TIM2 | 8 | SR2 | 8 | $04D2 |
$D3 | TIM3 | 8 | SR3 | 8 | $04D3 |
$D4 | TIM4 | 5 | |||
$E0 | RXD | ||||
$E1 | RXE | 6 | |||
$E2 | RXC | 8 | $04E2 | ||
$E3 | TXD | 11 | $04E3 | ||
$E4 | TXC | 8 | $04E4 | ||
$E5 | UIT | 8 | UMK | 7 | $04E5 |
$E6 | UAK | 7 | $04E6 | ||
$F0 | SPS0 | 8 | SPS0 | 16 | $04F0 (LSB), $04F1 (MSB) |
$F1 | SPD0 | 8 | SPD0 | 8 | |
$F2 | SPS1 | 8 | SPS1 | 16 | $04F2 (LSB), $04F3 (MSB) |
$F3 | SPD1 | 8 | SPD1 | 8 |
Read
$77 SCI 16bits  Screen Informations
$B0 MIDÂ 16bit Machine IdentificationÂ
Write
$77 Â SCM 8bits Screen Mode ($00: 640x64 pixels, $01: 640x480 pixels)
$B7 Â ROM 8bits Read Only Memory (bit 0 : $00-$1F, bit 2: $40-$5F, bit 3: $60-$7F, ... bit 7 : $E0-$FF, read-only if reset)
$B2 Â MVP 16bits Memory Violation Protection (1bit for each page of the first 4K, read-only if reset)
$C0  ES0 16bits  Extended segment 0 register (overwrites SR0)
$C1  ES1 16bits  Extended segment 1 register (overwrites SR1)
$C2  ES2 16bits  Extended segment 2 register (overwrites SR2)
$C3  ES3 16bits  Extended segment 3 register (overwrites SR3)
Advanced Memory Management Unit
The MVP and ROM registers are intend to protect memory against system violation.
The MVP allows writing in the first 4K of bank $20. Reset, Interrupt and RST instructions set this register to $FF.
The OZ calls are allowed to write in this area, they restore this register state on exit.
Application or user code cannot write in this area, if so, an interrupt is fired and MVP flag is set in INT (MVP flag replaces A19 bit, unused).
This feature ensure a strong system stability.
The ROM register hold the Read-Only configuration of 512K areas in the first 4M range.
Bit reset stands for a read only area. Each bit cover a 512K area.
Bit 0 : $00-$1F area
Bit 1 : $20-$3F area
Bit 2 : $40-$5F area
Bit 3 : $60-$7F area
Bit 4 : $80-$9F area
Bit 5 : $A0-$BF area
Bit 6 : $C0-$DF area
Bit 7 : $E0-$1F area
Screen
Resolution
Screen resolution is set by the SCM register, mode 0, default, is the standard 640x64 pixels panel.
Mode 1, VGA, the choice of the FPGA platform.
Mode 2, WVGA, is planned since 800x480 pixels resolution are a quite common LCD available (for future portable).
The blink returns screen width and height with SCW and SCH registers.
SBF
The screen base file is held in one bank.
All the screen registers are still addressed in the first 4M range.
SBR width becomes 8 bits with a 16K granularity.
128 words of 16 bits hold one line, minimal pixel width is 128x6 : 768 pixels, maximum 800 pixels if HIRES characters are used for the map.
15K are required to hold the 480 pixel lines of 60 characters.
The 1K left is used to hold the screen driver data (numbers of windows are increased...).
OZ window and MTH
OZ window and Menu window are horizontal. A vertical layout like original Z88 is not required and waste display space.
Top line : MENU window displaying Application names then the commands
Bottom line : OZ window displaying the system flags like Country, batteries, CAPS, CLI...
Control
Platform identification is performed reading the TYP register returning id ($FF for a Z88 portable).
Since memory is a large SDRAM chip, operating system area have to be write protected.
Memory Bank Switching
Extended segment registers (ESR) performs the bank switching up to 65536*16K, 1GB memory range.
Those ESR have a 16 bits width and lowest 8 bits overwrite the standard segments registers keeping backward compatibility.
SPI controller
Up to 4 SPI controller are implemented in the blink, actually only two are fitted.
Two ports by controller. One port for control/status of the controller (SPS0 or SPS1), one for data i/o (SPD0 or SPD1).
By default, controller 0 is wired to the internal serial flash (intended for FPGA bitstream update).
Controller 1 is wired to the primary SD card (intended for OZ loading).
Each controller has a CRC 16 and 32 calculation facility.
Remaining controllers are intended for future additional SD card slots.
UART update
UART implementation is backward compatible. UTEST bit implementation allows high-speed additional baudrates. Up to 500,000 bauds are allowed. A special 31.5 bauds speed allows MIDI implementation.
The serial signals are directly wired to a FTDI FT232R chip allowing UART USB link.