ref: 7af5442d3b031a3f81ea5c25c88f99692fb16822
dir: /sys/src/games/blit/mmap/
- main CPU is a MC68000 running at 8 MHz. the exact clock speed is most likely one of: 7.9872, 7.68 or 7.3728 MHz (to divide to 19200 baud) - display is 800x1024, refreshed at 30 Hz (60 Hz interlaced). it simply displays the 100K framebuffer from the address given in register 030. - the host is connected through a UART running at 19200 baud. - the keyboard is connected through a UART running at an unknown baudrate. - the mouse is connected through some unknown circuitry. memory map start end purpose 0x00000 0x00008 see register 050 below 0x00008 0x40000 RAM (256K) 0x40000 ??? ROM (24K ?) (not known if mirrored) 0x60000 ??? memory mapped I/O mmio addresses (in *octal*): 0000 16-bit mouse y 0002 16-bit mouse x 0011 8-bit terminal UART status/control (MC 6850 ACIA) 0013 8-bit terminal UART data the software uses 2 stop bits, no parity, 8 bits; clock divided by 16 0021 8-bit mouse buttons bit 0: rmb bit 1: mmb bit 2: lmb reading clears the mouse interrupt 0025 8-bit second copy of 0021 (?) 0027 8-bit ??? only the ROM binaries contain references to 0025, 0027 in buttons.c. the corresponding source code appears to have been deleted. possibly some older variant of the button hardware? 0030 16-bit start address of framebuffer divided by 4 (800*1024/8 = 100K bytes) 0040 16-bit status/control register of display bit 0: invert display with this bit set 0 bits are white and 1 bits are black (most software does this). 0050 16-bit writing different values makes 0-8 either mapped to 0x40000 or error out (details unclear) resets so that they map to the reset vector at 0x40000. 0056 8-bit some kind of sound-making device (standard programmable timer + piezoelectric speaker?) 0156 referenced by demo pacman. 0256 0060 8-bit keyboard status/control register (MC 6850 ACIA) the software uses 2 stop bits, no parity, 8 bits; clock divided by 16 0062 8-bit keyboard data register 0070 16-bit? acknowledge vblank interrupt; software writes 0 tx to the keyboard sets the 7 lights and can also ring the bell. could deduce the order of lights from diag.c. writing 2 is used to sound the bell. irq lines; using the 68k autovectoring vector 1 (0x64) is vblank vector 2 (0x68) is keyboard vector 4 (0x70) is mouse buttons vector 5 (0x74) is uart MC 6850 bits: +0 (r) status register bit 0: receive buffer full bit 1: transmit buffer empty bit 2: data carrier detected (inverted) bit 3: clear-to-send (inverted) bit 4: framing error bit 5: receiver overrun bit 6: parity error bit 7: irq active +0 (w) control register bit 1-0: clock divider 00: /1 01: /16 10: /64 11: master reset bit 4-2: parity and stop bits (see datasheet) bit 6-5: RTS/ is high only if these bits are 10 TX interrupts are enabled only if these bits are 01 break is transmitted continuously if these bits are 11 bit 7: RX interrupt enabled