Reclaim memory

CLAUDE.md

@@ -94,3 +94,23 @@ In `key_action.h`:
 ## Code Review Philosophy
 
 Focus on functional aspects, not nitpicks. Only flag magic constants if they're used in multiple places and may need future changes. Don't require comments unless truly necessary.
+
+## UHK80 / Zephyr Dev Environment — Findings
+
+Key gotchas discovered while setting up:
+
+- **Re-run `./build.sh update` after any branch/manifest switch.** The west modules (zephyr, nrf, …)
+  are pinned per `west_nrfsdk.yml`; if they don't match the current checkout, CMake configure fails
+  with `Error finding board: uhk-80-right ... Malformed "build" section ... SchemaError`. This is a
+  Zephyr version mismatch, not a `board.yml` bug — `./build.sh update` (west update + patch) fixes it.
+- **Single-device builds run in the foreground** (`./build.sh right build`), which is easiest for
+  testing; multi-device (`left right dongle`) fans out into tmux `buildsession` panes.
+- **Dongle link depends on `keyboard/` sources.** `right/src/slave_drivers/kboot_driver.c` is compiled
+  for all UHK80 targets, but `device/src/CMakeLists.txt` only compiles `keyboard/*.c` (which includes
+  `uart_modules.c`) for left/right, **not** the dongle. So any symbol `kboot_driver.c` pulls from
+  `uart_modules.c` (e.g. the `KbootUart_*` UART-transport functions) must be stubbed/guarded for the
+  dongle or the dongle link fails with `undefined reference`.
+- **Agent npm shadow.** `lib/agent` is nested inside this repo; the firmware root's `node_modules/npm`
+  (11.8.0, pinned by the root lockfile) shadows nvm's npm during the Agent build and trips its
+  `check-node-version` (>=11.13.0). Fix: `npm install npm@11.13.0 --no-save --no-package-lock` in the
+  firmware root. Details in the reference doc above.

device/prj.conf.overlays/nrf_shared.conf

@@ -8,7 +8,6 @@ CONFIG_INIT_STACKS=y
 CONFIG_LOG=y
 CONFIG_LOG_CMDS=y
 CONFIG_LOG_MODE_DEFERRED=y
-CONFIG_LOG_BUFFER_SIZE=2048
 CONFIG_LOG_BACKEND_SHOW_COLOR=y
 CONFIG_LOG_RUNTIME_FILTERING=y
 
@@ -38,19 +37,31 @@ CONFIG_BT_FILTER_ACCEPT_LIST=y
 CONFIG_BT_CTLR_SDC_MAX_CONN_EVENT_LEN_DEFAULT=2500
 CONFIG_BT_CTLR_SDC_CENTRAL_ACL_EVENT_SPACING_DEFAULT=2500
 
-# increase these to make multiple connections more reliable
-# this is a generic ai advice. 
-CONFIG_BT_ATT_TX_COUNT=10
-CONFIG_BT_CONN_TX_MAX=6
-CONFIG_BT_L2CAP_TX_BUF_COUNT=12
-
-# negotiate larger MTU for NUS
+# BLE buffer counts, sized for ~2 active links (L=2) with double buffering
+# (D=2), no HCI fragmentation (LL unit == L2CAP MTU, so frags/PDU F=1). Each
+# line notes the constraint it must satisfy. BT_BUF_ACL_TX_COUNT (the HCI TX
+# credit window) is left at its default 3: it is capped by the controller's
+# BT_CTLR_SDC_TX_PACKET_COUNT and 3 credits already cover 2 links.
+# ATT TX PDUs in flight: >= L*D (freed on HCI handoff, not air-ack)
+CONFIG_BT_ATT_TX_COUNT=5
+# L2CAP signalling/SMP only (no CoC): a handful
+CONFIG_BT_L2CAP_TX_BUF_COUNT=4
+# HCI event RX: > BT_BUF_ACL_TX_COUNT (build assert)
+CONFIG_BT_BUF_EVT_RX_COUNT=6
+# ACL RX reassembly: 1+EXTRA >= L+1 (one/link + driver spare)
+CONFIG_BT_BUF_ACL_RX_COUNT_EXTRA=2
+
+# NUS packet sizing. We cap the link packet at MAX_LINK_PACKET_LENGTH=128
+# (link_protocol.h) rather than the DLE maximum, to save RAM and cut BLE latency.
+#   ACL buffer = MAX_LINK_PACKET_LENGTH + L2CAP(4) + ATT(3) = 135
+#   L2CAP MTU  = MAX_LINK_PACKET_LENGTH + ATT(3)            = 131
+# bt_conn.c caps the negotiated DLE tx length to CONFIG_BT_BUF_ACL_TX_SIZE.
 CONFIG_BT_USER_DATA_LEN_UPDATE=y
-CONFIG_BT_BUF_ACL_RX_SIZE=251
-CONFIG_BT_BUF_ACL_TX_SIZE=251
-CONFIG_BT_L2CAP_TX_MTU=247
+CONFIG_BT_BUF_ACL_RX_SIZE=135
+CONFIG_BT_BUF_ACL_TX_SIZE=135
+CONFIG_BT_L2CAP_TX_MTU=131
 
-# allow BLE buffering
+# inbound long-write (config transfer) queue depth
 CONFIG_BT_ATT_PREPARE_COUNT=4
 
 # store BLE link keys in flash
@@ -61,9 +72,12 @@ CONFIG_FLASH_MAP=y
 CONFIG_SETTINGS=y
 CONFIG_NVS=y
 
-# prevent dropped messages 
-CONFIG_LOG_BUFFER_SIZE=4096
-CONFIG_SEGGER_RTT_BUFFER_SIZE_UP=4096
+# Log/RTT buffers kept small to save RAM (we are tight on RAM). If these small
+# buffers drop messages under bursty logging, raise the logging thread priority
+# at runtime with the "uhk log priority high" shell command rather than enlarging
+# the buffers.
+CONFIG_LOG_BUFFER_SIZE=1024
+CONFIG_SEGGER_RTT_BUFFER_SIZE_UP=512
 
 CONFIG_SERIAL=y
 

device/src/bt_conn.c

@@ -291,10 +291,13 @@ static void enableDataLengthExtension(struct bt_conn *conn) {
     data_len = BT_LE_DATA_LEN_PARAM_MAX;
 
     /**
-     * This configures actual transmission length.
+     * Configures actual transmission length. Cap the payload to our reduced ACL
+     * buffer (CONFIG_BT_BUF_ACL_TX_SIZE) rather than the DLE max of 251: we never
+     * send larger packets and shorter PDUs mean lower latency.
      *
-     * We don't want it too high in order to prevent scheduling conflicts between multiple links.
+     * tx_max_time kept low to avoid scheduling conflicts between multiple links.
      * */
+    data_len->tx_max_len = CONFIG_BT_BUF_ACL_TX_SIZE;
     data_len->tx_max_time = 2500;
 
     int err = bt_conn_le_data_len_update(conn, data_len);

device/src/link_protocol.h

@@ -8,12 +8,16 @@
 
 // Macros:
 
-// 251 = maximum BLE packet length with data length extension
+// Maximum deserialized message length (header + payload) that fits in a single
+// BLE notification / UART bridge frame. We deliberately keep this well below the
+// DLE maximum (244 with a 251-byte ACL buffer) to save RAM (messenger-queue
+// regions, nus/uart buffers) and to shorten BLE packets for lower latency.
 // 4 bytes reserved for L2CAP header
 // 3 bytes reserved for ATT header
 // https://devzone.nordicsemi.com/f/nordic-q-a/111900/maximum-nus-packet-payload-with-ble-data-length-extensio
-// Should equal `CONFIG_BT_BUF_ACL_RX_SIZE - L2CAP_HEADER_SIZE - ATT_HEADER_SIZE`, otherwise something is wrong
-#define MAX_LINK_PACKET_LENGTH 244
+// Should equal `CONFIG_BT_BUF_ACL_RX_SIZE - L2CAP_HEADER_SIZE - ATT_HEADER_SIZE`
+// (i.e. 135 - 4 - 3), otherwise something is wrong.
+#define MAX_LINK_PACKET_LENGTH 128
 
 // Typedefs: