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bridge: each node draws its own receiver noise #23

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Merged
A13xB0 merged 1 commit into from
Sep 9, 2026
Merged

bridge: each node draws its own receiver noise #23

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14 changes: 14 additions & 0 deletions bridge/main.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,15 @@ void loop();
// Defined by the host variant.
extern uint32_t g_sim_millis;
int g_stuck_irq_ms = 0;
// The receiver-noise stream the chip model draws from. Distinct per node so
// two nodes do not read the same "random" bytes at the same instants - which
// is what seeds each node's RNG, its CSMA backoff and its advert jitter. Left
// at 0 the whole mesh drew one stream and every node's timing was correlated.
// Defaults to the identity seed, which the simulator already makes distinct
// per node, so a node differs without the simulator having to send anything;
// XORed so it is not literally the number the keypair is also derived from.
uint64_t g_noise_seed = 0;
bool g_noise_seed_set = false;
extern int g_sf;
extern float g_bwKHz;
extern int g_cr;
Expand Down Expand Up @@ -181,6 +190,7 @@ int main(int argc, char** argv) {
// identity. The simulator sends a value that fits in 32 bits either way,
// so a seed it sends means the same thing on every platform.
else if (!strcmp(argv[i], "--seed")) g_identity_seed = strtoull(next(), nullptr, 10);
else if (!strcmp(argv[i], "--noise-seed")) { g_noise_seed = strtoull(next(), nullptr, 10); g_noise_seed_set = true; }
else if (!strcmp(argv[i], "--sf")) g_sf = atoi(next());
else if (!strcmp(argv[i], "--bw-khz")) g_bwKHz = (float)atof(next());
else if (!strcmp(argv[i], "--cr")) g_cr = atoi(next());
Expand Down Expand Up @@ -217,6 +227,10 @@ int main(int argc, char** argv) {
// Only if asked for on the command line. A build compiled as a faulty
// variant already has its value, and overwriting it with the flag default
// silently turned that whole variant back into a well-behaved one.
// Per-node receiver noise, so the mesh does not run on one shared stream.
sim_hal.chip().setNoiseSeed(g_noise_seed_set ? g_noise_seed
: (g_identity_seed ^ 0x9E3779B97F4A7C15ULL));

if (g_stuck_irq_ms > 0) sim_hal.chip().setStuckIrqMs((uint32_t)g_stuck_irq_ms);
setup();
drainTx();
Expand Down
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