refactor: replace the TICK_MS global with app.setTickInterval()

A magic global that the runtime reads once at startup could not be changed later, gave
no feedback when misspelled, and was a second spelling of a mechanism the sibling
firmware already had. app.setTickInterval(ms) clamps to 33..3600000, takes 0 to stop,
and errors when on_tick() is not defined -- by the time init() runs the chunk body has
finished, so a missing callback is a typo rather than a race.

Also drops the code comments pointing at the other repo. Where the two APIs agree or
differ belongs in docs/lua-api-parity.md; a comment beside a constant explaining that
another firmware picked the same number is noise a reader here cannot act on.

README.md

@@ -39,7 +39,7 @@ firmware only draws a fallback screen if it cannot start.
 
 Apps define `init()`, which is required, plus optional `draw()` (~30fps cap), `on_touch_down(x, y)`,
 `on_touch_up(x, y)`, `on_touch(x, y)` (tap alias, fired on release), and `on_tick()`
-(enabled by setting `TICK_MS`). Call `sys.exit()` to return to the launcher.
+(enabled by `app.setTickInterval(ms)`). Call `sys.exit()` to return to the launcher.
 
 `require` reads from the SD card: `/apps/<name>/?.lua` first, then `/lib/?.lua`.
 

docs/lua-api-parity.md

@@ -12,7 +12,7 @@ Compared against crosspoint-reader at `src/util/lua/LuaBindings*.cpp`.
 `fs.listDirs`, `fs.listFiles`, `fs.exists`, `fs.readFile`, `fs.writeFile`,
 `gui.width`, `gui.height`, `gui.fillRect`, `gui.drawRect`, `gui.drawLine`,
 `sys.millis`, `sys.delay`, `sys.exit`, `log.debug/info/error`, the whole `http` table,
-and the `init()` / `draw()` / `on_tick()` callbacks. `init()` is required in both, so a
+`app.setTickInterval`, and the `init()` / `draw()` / `on_tick()` callbacks. `init()` is required in both, so a
 misspelled entry point is an error rather than an app that quietly draws nothing.
 
 ## Deliberate differences
@@ -38,7 +38,6 @@ Each of these is the same concept spelled two ways. Fixing them means changing o
 
 | Concern | crosspoint-reader | esp32-lcd | Suggested resolution |
 |---|---|---|---|
-| Tick interval | `app.setTickInterval(ms)` | global `TICK_MS` | Pick one mechanism. |
 | `wifi.status()` | returns a **string** | returns a **table** of state/ssid/ip/rssi | Same name, incompatible types — the sharpest edge here. This repo added `isConnected()` and `localIP()` so the crosspoint idioms work either way. |
 | `wifi.connect()` | no arguments, uses stored credentials | `(ssid, password)`, saves them | Both are wanted: a no-argument reconnect and an explicit join. |
 | `fs.readFile` cap | 50000 bytes | 65536 bytes | Arbitrary in both. |

scripts/gen_lua_stubs.py

@@ -123,7 +123,7 @@ def render(modules):
             "-- Callbacks an app may define as globals:",
             "--   init()                   once, before the first draw (required)",
             "--   draw()                   every 33 ms while the app runs",
-            "--   on_tick()                every TICK_MS, when that global is set",
+            "--   on_tick()                at the interval app.setTickInterval() asked for",
             "--   on_touch_down(x, y)      finger down",
             "--   on_touch_up(x, y)        finger up",
             "--   on_touch(x, y)           tap, fired on release like a click",

sdcard/apps/hello/main.lua

@@ -1,12 +1,11 @@
 local ui = require("ui")
 
-TICK_MS = 1000
-
 local seconds = 0
 -- Draws straight to the panel rather than through components, so it reads the theme.
 local theme = ui.theme
 
 function init()
+  app.setTickInterval(1000)
   gui.clear(theme.bg)
   gui.drawText("hello from sd card", 10, 10, theme.fg, theme.bg)
   gui.drawText("touch the screen", 10, 30, theme.muted, theme.bg)

sdcard/apps/launcher/main.lua

@@ -3,9 +3,8 @@ local ui = require("ui")
 local screen
 local clock
 
--- Twice a second, so the seconds digit never visibly lags. WiFi and SNTP run in the
--- background; until the clock means something the placeholder holds its width.
-TICK_MS = 500
+-- Until the clock means something the placeholder holds its width; WiFi and SNTP run
+-- in the background.
 local PLACEHOLDER = "--:--:--"
 
 -- Rows are interactive containers rather than plain buttons, so each can carry a
@@ -20,6 +19,7 @@ local function appRow(name)
 end
 
 function init()
+  app.setTickInterval(500)  -- twice a second, so the seconds digit never visibly lags
   -- Fixed width: drawText paints an opaque background only under its own glyphs, so a
   -- shorter label would leave the tail of the previous one on screen.
   clock = ui.text(PLACEHOLDER, {w = gui.textWidth(PLACEHOLDER), color = ui.theme.muted})

sdcard/apps/settings/main.lua

@@ -1,7 +1,5 @@
 local ui = require("ui")
 
-TICK_MS = 50
-
 local INSET = 30
 
 local screen, message
@@ -242,6 +240,7 @@ function buildKeyboard()
 end
 
 function init()
+  app.setTickInterval(50)  -- calibration samples the raw panel between draws
   buildMenu()
 end
 

src/lua/bindings/http.cpp

@@ -1,10 +1,7 @@
-// HTTP client. Signatures match crosspoint-reader's `http` table exactly, so a script
-// that talks to a server runs on either device; see docs/lua-api-parity.md.
-//
-// Unlike crosspoint, certificates are verified against the root bundle already
-// embedded in the framework. Nothing here lets a script turn that off: the signatures
-// have no options table to hang it on, and the one caller that would want it most --
-// a firmware update -- is the one that can least afford an unauthenticated peer.
+// HTTP client. Certificates are verified against the root bundle already embedded in
+// the framework, and nothing here lets a script turn that off: the signatures have no
+// options table to hang it on, and the one caller that would want it most -- a firmware
+// update -- is the one that can least afford an unauthenticated peer.
 
 #include <HTTPClient.h>
 #include <SD.h>
@@ -19,7 +16,7 @@ extern const uint8_t rootca_crt_bundle_start[] asm("_binary_x509_crt_bundle_star
 
 namespace {
 
-constexpr size_t MAX_RESPONSE = 50000;  // matches crosspoint's cap, so limits behave alike
+constexpr size_t MAX_RESPONSE = 50000;
 constexpr uint32_t TIMEOUT_MS = 60000;
 constexpr int REDIRECT_LIMIT = 5;
 constexpr size_t DOWNLOAD_CHUNK = 2048;
@@ -64,8 +61,8 @@ void applyHeaders(lua_State* L, int index, HTTPClient& http) {
 }
 
 // get/head/delete take headers in slot 2; post/patch take a body there and headers in 3.
-// crosspoint reinterprets a string in slot 2 as a body for every method, which turns a
-// mistyped header table into a silent protocol error, so this rejects it instead.
+// A string in slot 2 of a bodyless method is rejected rather than reinterpreted, since
+// a mistyped headers table would otherwise become a silent protocol error.
 int request(lua_State* L, const char* method, bool bodyExpected) {
   const char* url = luaL_checkstring(L, 1);
   const char* body = "";
@@ -122,8 +119,8 @@ int fail(lua_State* L, const char* message) {
   return 2;
 }
 
-// Only the keys crosspoint accepts, and rejecting the rest: a misspelled `sha256` that
-// was quietly ignored would report a verified download that verified nothing.
+// Unknown keys are rejected: a misspelled `sha256` that was quietly ignored would
+// report a verified download that verified nothing.
 bool readOptions(lua_State* L, int index, uint32_t& maxBytes, uint32_t& expectedSize,
                  String& sha256, const char*& error) {
   luaL_checktype(L, index, LUA_TTABLE);

src/lua/bindings/sys.cpp

@@ -96,12 +96,32 @@ static int logAt(lua_State* L, const char* level) {
   return 0;
 }
 
+// Rejected rather than ignored when on_tick is absent: the chunk body has already run
+// by the time init() calls this, so a missing callback is a typo, not a race.
+static int l_app_setTickInterval(lua_State* L) {
+  lua_Integer requested = luaL_checkinteger(L, 1);
+  if (requested <= 0) {
+    app(L)->setTickInterval(0);
+    return 0;
+  }
+  lua_getglobal(L, "on_tick");
+  bool hasTick = lua_isfunction(L, -1);
+  lua_pop(L, 1);
+  if (!hasTick) return luaL_error(L, "app.setTickInterval() requires on_tick()");
+
+  uint32_t interval = requested < (lua_Integer)LuaApp::MIN_TICK_MS ? LuaApp::MIN_TICK_MS
+                      : requested > (lua_Integer)LuaApp::MAX_TICK_MS ? LuaApp::MAX_TICK_MS
+                                                                     : (uint32_t)requested;
+  app(L)->setTickInterval(interval);
+  return 0;
+}
+
 static int l_log_debug(lua_State* L) { return logAt(L, "debug"); }
 static int l_log_info(lua_State* L) { return logAt(L, "info"); }
 static int l_log_error(lua_State* L) { return logAt(L, "error"); }
 
-// Parity with crosspoint: sleeping is the one thing a script cannot express itself,
-// since the runtime owns the loop.
+// Sleeping is the one thing a script cannot express itself, since the runtime owns
+// the loop.
 static int l_sys_delay(lua_State* L) {
   delay(luaL_checkinteger(L, 1));
   return 0;
@@ -155,7 +175,15 @@ void registerSys(lua_State* L) {
   luaL_newlib(L, lib);
   lua_setglobal(L, "sys");
 
-  // Too small to deserve its own translation unit.
+  // These two are too small to deserve their own translation units.
+  static const luaL_Reg appLib[] = {
+      // --- Sets how often on_tick() runs. Errors when on_tick is not defined.
+      // @param intervalMs integer 0 stops ticking; anything else is clamped to 33..3600000.
+      {"setTickInterval", l_app_setTickInterval},
+      {nullptr, nullptr}};
+  luaL_newlib(L, appLib);
+  lua_setglobal(L, "app");
+
   static const luaL_Reg logLib[] = {
       // --- Writes a debug line to the serial log.
       // @param message string

src/lua/bindings/wifi.cpp

@@ -85,8 +85,8 @@ static int l_wifi_status(lua_State* L) {
   return 1;
 }
 
-// Parity with crosspoint, whose wifi.status() returns a bare string and so needs these
-// as separate calls. Here they are shorthands for fields status() already carries.
+// Shorthands for two fields status() already carries, for scripts that want one answer
+// without unpacking a table.
 static int l_wifi_isConnected(lua_State* L) {
   lua_pushboolean(L, WiFi.status() == WL_CONNECTED);
   return 1;

src/lua/lua_app.cpp

@@ -91,6 +91,9 @@ bool LuaApp::takeFailure() {
 
 bool LuaApp::load(const char* path) {
   closeState();
+  // Cleared per app: the interval outlives the app that set it, so a ticking app
+  // followed by one that never ticks would keep calling a nil global.
+  tickIntervalMs = 0;
   // The launcher tap may still be down; swallow that gesture's release.
   lastTouched = true;
   ignoreRelease = true;
@@ -109,29 +112,22 @@ bool LuaApp::load(const char* path) {
     return false;
   }
   if (!callGlobal(path)) return false;  // run chunk body
-  // Required, as on crosspoint-reader: an app whose entry point is misspelled would
-  // otherwise start, draw nothing, and give no hint why.
+  // An app whose entry point is misspelled would otherwise start, draw nothing, and
+  // give no hint why.
   if (!hasGlobal("init")) {
     fail("Missing init()");
     return false;
   }
   lua_getglobal(state, "init");
   if (!callGlobal("init")) return false;
-  // Cleared first: the interval outlives the app that set it, so a ticking app
-  // followed by one without on_tick would otherwise keep calling a nil global.
-  tickIntervalMs = 0;
-  if (hasGlobal("on_tick")) {
-    tickIntervalMs = DEFAULT_TICK_MS;
-    lua_getglobal(state, "TICK_MS");
-    if (lua_isinteger(state, -1)) {
-      tickIntervalMs = std::max<uint32_t>(lua_tointeger(state, -1), DRAW_INTERVAL_MS);
-    }
-    lua_pop(state, 1);
-    nextTickMs = millis() + tickIntervalMs;
-  }
   return running();
 }
 
+void LuaApp::setTickInterval(uint32_t intervalMs) {
+  tickIntervalMs = intervalMs;
+  nextTickMs = millis() + intervalMs;
+}
+
 void LuaApp::registerBindings() {
   registerGui(state);
   registerSys(state);

src/lua/lua_app.h

@@ -28,6 +28,12 @@ class LuaApp {
   // can leave the message on screen long enough to read.
   bool takeFailure();
 
+  // Set from Lua by app.setTickInterval(); 0 stops the ticks.
+  void setTickInterval(uint32_t intervalMs);
+
+  static constexpr uint32_t MIN_TICK_MS = 33;        // no point ticking faster than a draw
+  static constexpr uint32_t MAX_TICK_MS = 3600000;   // an hour
+
   // Panel geometry in its rotation-0 frame; calibration is stored in this space
   // so rotating the UI never needs a recalibration.
   static constexpr int16_t PANEL_W = 320;
@@ -57,7 +63,6 @@ class LuaApp {
   uint32_t nextDrawMs = 0;
 
   static constexpr uint32_t DRAW_INTERVAL_MS = 33;
-  static constexpr uint32_t DEFAULT_TICK_MS = 100;  // used when on_tick exists without TICK_MS
 
   void registerBindings();
   bool callGlobal(const char* name, int nargs = 0);

stubs/esp32lcd.lua

@@ -4,6 +4,13 @@
 -- Point your editor's Lua language server at this file to get completion for the
 -- firmware API inside sdcard/apps and sdcard/lib.
 
+---@class applib
+app = {}
+
+--- Sets how often on_tick() runs. Errors when on_tick is not defined.
+---@param intervalMs integer 0 stops ticking; anything else is clamped to 33..3600000.
+function app.setTickInterval(intervalMs) end
+
 ---@class fslib
 fs = {}
 
@@ -299,7 +306,7 @@ function wifi.forget() end
 -- Callbacks an app may define as globals:
 --   init()                   once, before the first draw (required)
 --   draw()                   every 33 ms while the app runs
---   on_tick()                every TICK_MS, when that global is set
+--   on_tick()                at the interval app.setTickInterval() asked for
 --   on_touch_down(x, y)      finger down
 --   on_touch_up(x, y)        finger up
 --   on_touch(x, y)           tap, fired on release like a click

test/fake_device.lua

@@ -13,6 +13,7 @@ local device = {
   rotation = 0,
   theme = "light",
   clockSynced = false,
+  tickInterval = 0,
   timezone = "UTC0",
   raw = nil,          -- pending raw touch reading, {x, y} or nil
   networks = {},      -- what wifi.scan() returns
@@ -99,7 +100,14 @@ function device.install()
     forget = function() device.connected = nil return saved() end,
   }
 
-  log = {info = function() end}
+  app = {
+    setTickInterval = function(ms)
+      assert(ms == 0 or on_tick, "setTickInterval without on_tick")
+      device.tickInterval = ms
+    end,
+  }
+
+  log = {debug = function() end, info = function() end, error = function() end}
 
   return device
 end