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  SBC7 v1.3.7 Stable

  bcox released this 2026-04-12 19:39:44 +00:00 | 13 commits to main since this release

  Signed by bcox

  GPG key ID: 1C87BFF7FAC89089

  If v1.2.0 was the release where SBC7 went from simulator to silicon, and
  v1.3.x is the release series where it became genuinely useful to live with,
  then v1.3.7 is the one where you can actually sit down at the thing, write
  a BASIC program, save it to disk, come back later, and load it again. That
  may sound modest. For a 7-bit computer, it is a complete arc. The gap
  between v1.3.1 and v1.3.7 spans six tagged versions that never made a
  public release, which means this notes entry covers rather a lot of ground.
  Here is all of it.

  (Why no v1.3.2 through v1.3.6? Because each one found something broken in
  the thing that had just shipped. Consider them the iterative part of
  "iterative development," now over.)

  Real-Time Clock

  The SBC7 has a clock now. The RTC peripheral (ports 48-55) tracks year,
  month, day, hour, minute, and second, seeded at reset from the host system's
  UTC clock in the emulator and from the MiSTer ARM HPS on hardware. There is
  no battery -- the clock does not survive power loss -- but it is accurate
  while it runs, it handles leap years correctly through 2127, and the boot
  banner now prints the date and time alongside the RAM and ROM sizes.

  The latch mechanism deserves a mention: writing CONTROL with LATCH=1
  snapshots all six time fields atomically, so a burst of IN instructions
  cannot catch a carry propagating from 23:59:59 to 00:00:00 in mid-read.
  This is the kind of detail that only becomes obvious after you have
  debugged the alternative.

  Gamepad Controller Port

  Two NES-style controller ports (ports 56-58) with a change-of-state
  interrupt at RST 5. D-pad, A, B, Select, and Start per controller; the ROM
  installs a bare RETI at the RST 5 vector, so programs can simply HALT and
  wake on any button event. On MiSTer, joystick_0 and joystick_1 from the HPS
  map to the two pads. In the emulator, player 1 is on the keyboard (arrows
  for D-pad, Z/X for A/B, A/S for Select/Start).

  Display Hardware: Color, Font, and Vertical Blanking

  This release effectively rebuilds the VGA output from the front panel
  inward.

  Indexed color per character cell. Every cell on the 64x24 display now
  has its own foreground and background color, selected from a 16-entry
  palette. The attribute byte format is compact: 3 bits of background (indices
  0-7) and 4 bits of foreground (indices 0-15), which gives brighter options
  for text while keeping dark backgrounds the sensible default. The palette
  itself lives in the color bank and is updated from the CPU's write side
  during vertical blanking.

  Per-channel gamma-corrected color expansion. The 7-bit native color
  encoding (2R 3G 2B) is expanded to 24-bit for display with different gamma
  curves per channel: R=1.6, G=1.5, B=1.4. The human eye does not perceive
  linear intensity as linear brightness, and the three channels do not agree
  on exactly how wrong the linear approximation is. The result is a more
  natural-looking palette, particularly in the mid-range colors that text
  actually lives in.

  Font data moved to ROM bank 7. The 128-glyph character set is now stored
  in a dedicated ROM bank rather than in the VGA hardware itself. The
  CHAR_BANK register (port 39) selects which bank feeds the character renderer,
  and the default points at ROM bank 7. This means custom fonts are possible
  by writing glyph data (128 glyphs x 14 rows) into any RAM bank and pointing
  port 39 at it.

  Vertical blanking interrupt at RST 4. The VGA controller fires RST 4
  at the start of each vblank, about 60 times per second. The ROM installs a
  bare RETI by default; programs that need synchronized palette updates or
  animation timing can install their own handler at &00:20. A boot-time RETI
  fix that had been shipped with a wrong opcode is also corrected here.

  Console control characters. The console driver gained cursor movement
  codes ($01-$06 for left/right/up/down), HOME ($0B), form-feed / clear-screen
  ($0C), foreground color select ($10-$1F for palette indices 0-15), and color
  swap/reset ($0E-$0F). Keyboard handling grew corresponding support for arrow
  keys, the Home key, Ctrl+digit color codes, and a properly timed ESC
  timeout. Scanline registers (ports 33-34) expose the current beam position
  and the vblank flag as readable values, useful for timing-sensitive code.

  ROM capability flags. The signature block at &7F:7F now carries a
  feature-flags byte: bit 0 = banking, bit 1 = disk, bit 2 = RTC, bit 3 =
  gamepad, bit 4 = color VGA. Programs that need to run on multiple ROM
  versions can read this byte to confirm what they are dealing with before
  trying to use features that may not be present.

  Filesystem: Full Read/Write

  S7FS now has a complete read/write story. The previous release had mount,
  open, read, close, directory listing, and free-space query. This release
  adds OPENW (open existing file for read/write), CREATE (create or truncate),
  WRITE, REMOVE, MKDIR, RMDIR, and SEEK -- syscalls 16 through 22. Timestamps
  are live: the ROM's _rtc_stamp helper reads the RTC and writes the
  creation timestamp when a file or directory is created, and the modification
  timestamp when a write-mode file is closed.

  The write driver is spread across ROM banks 4 and 5 to keep each bank within
  the 2 KB limit. Write operations go through the same FAT cluster-chain
  machinery as reads, with bank 8 used as scratch space during sector transfers.
  SEEK takes a 28-bit byte offset in the DSK_LBA registers, shared with the
  OPENW return value so appending is a single extra syscall.

  A race condition in the interrupt vector setup and a multi-cluster read bug
  in the filesystem driver are both fixed here.

  TinyBASIC: DIR, SAVE, and LOAD

  TinyBASIC now has a complete file I/O story at the BASIC level.

  DIR lists files with sizes and modification timestamps in long format,
  optionally targeting a subdirectory or a second drive. Directories are shown
  in brackets. Timestamps have quarter-hour resolution, which is the finest
  the RTC format stores.

  SAVE writes the current program to a named file on disk, in the same
  format that LIST produces. If the file already exists it is overwritten.

  LOAD reads a program back from disk, clearing whatever was in memory
  first. Files that span multiple disk clusters are handled transparently;
  the LOAD command walks the FAT chain as many times as needed. A related
  fix to the TIB (terminal input buffer) memory layout resolved an overlap
  with the B segment that had been quietly waiting to cause trouble in
  multi-cluster loads.

  Demos and Examples

  The factory disk now ships with an oscilloscope-style sine wave demo and
  palette display and logo display programs. The sine wave demo is a reasonable
  stress test for VBI-synchronized output and makes a good screensaver if you
  are the sort of person who runs a 7-bit computer unattended. The palette
  display shows all 16 palette entries with their expanded RGB values, which is
  useful when tuning color output on new hardware.

  Build System

  The justfile has been merged into the Makefile. The build system is now a
  single make invocation for all targets, including the examples, the
  language interpreters, and the cross-compilation workflow. Existing
  make-based habits are unaffected; just is no longer required.

  MiSTer Fixes

  H7X loading and disk I/O on MiSTer both received fixes during this cycle.
  The color pipeline was also corrected to match the emulator's output, so
  what you see in emu7 is what you see on the DE10-Nano.

  Downloads

  • Source code (ZIP)
    1 download
  • Source code (TAR.GZ)
    2 downloads

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  • SBC7_20260412.zip
    3 downloads · 2026-04-12 19:39:51 +00:00 · 1.1 MiB