libsi: Reduce memory usage in command_table

Author: loopj

firmware/libsi/src/commands.c

@@ -1,83 +1,126 @@
 #include "si/commands.h"
 
+#define COMMAND_TABLE_SIZE 18
+
 enum {
-  COMMAND_STATE_IDLE,
-  COMMAND_STATE_RX,
-  COMMAND_STATE_TX,
-  COMMAND_STATE_ERROR,
+  BUS_STATE_UNKNOWN = 0,
+  BUS_STATE_IDLE,
+  BUS_STATE_BUSY,
+  BUS_STATE_ERROR,
 };
 
 struct command_entry {
+  uint8_t command;
   uint8_t length;
   si_command_handler_fn handler;
   void *context;
 };
 
-static uint8_t command_state                   = COMMAND_STATE_IDLE;
-static struct command_entry command_table[256] = {0};
+static uint8_t bus_state                                      = BUS_STATE_UNKNOWN;
+static struct command_entry command_table[COMMAND_TABLE_SIZE] = {0};
 static uint8_t command_buffer[SI_BLOCK_SIZE];
 static bool auto_tx_rx_transition = false;
 
+// Vaguely context-aware hash function
+static inline uint8_t hash_command(uint8_t command)
+{
+  // Reserve hash slots for universal commands
+  if (command == 0x00)
+    return 0;
+  if (command == 0xFF)
+    return 1;
+
+  // Hash all other commands to remaining slots
+  return (command % (COMMAND_TABLE_SIZE - 2)) + 2;
+}
+
+// Find a command entry by command id
+static struct command_entry *find_command(uint8_t command)
+{
+  uint8_t index = hash_command(command);
+
+  while (command_table[index].handler != NULL) {
+    if (command_table[index].command == command) {
+      return &command_table[index];
+    }
+    index = (index + 1) % COMMAND_TABLE_SIZE;
+  }
+  return NULL;
+}
+
 // Command handler TX completion callback
 static void on_tx_complete(int result)
 {
-  if (result == 0) {
-    command_state = COMMAND_STATE_IDLE;
+  // Update bus state based on result
+  bus_state = (result < 0) ? BUS_STATE_ERROR : BUS_STATE_IDLE;
 
-    // Check if we need to transition back to RX mode
-    if (auto_tx_rx_transition)
-      si_command_process();
-  } else {
-    command_state = COMMAND_STATE_ERROR;
-  }
+  // Transition back to RX mode if auto transition is enabled
+  if (auto_tx_rx_transition)
+    si_command_process();
 }
 
 // Command handler RX completion callback
 static void on_rx_complete(int result)
 {
   if (result == 0) {
     // Look up the command in the table
-    struct command_entry *command = &command_table[command_buffer[0]];
-    if (command->handler) {
+    struct command_entry *command = find_command(command_buffer[0]);
+    if (command && command->handler) {
       // Call the command handler
-      command_state = COMMAND_STATE_TX;
+      bus_state = BUS_STATE_BUSY;
       command->handler(command_buffer, on_tx_complete, command->context);
       return;
     }
   }
 
   // Error during command read or handler not found
-  command_state = COMMAND_STATE_ERROR;
+  bus_state = BUS_STATE_ERROR;
+
+  // Transition back to RX mode if auto transition is enabled
+  if (auto_tx_rx_transition)
+    si_command_process();
 }
 
 void si_command_register(uint8_t command, uint8_t length, si_command_handler_fn handler, void *context)
 {
-  command_table[command].length  = length;
-  command_table[command].handler = handler;
-  command_table[command].context = context;
+  uint8_t index = hash_command(command);
+
+  // Linear probing for collision resolution
+  while (command_table[index].handler != NULL && command_table[index].command != command) {
+    index = (index + 1) % COMMAND_TABLE_SIZE;
+  }
+
+  command_table[index].command = command;
+  command_table[index].length  = length;
+  command_table[index].handler = handler;
+  command_table[index].context = context;
 }
 
 uint8_t si_command_get_length(uint8_t command)
 {
-  return command_table[command].length;
+  struct command_entry *entry = find_command(command);
+  if (entry == NULL)
+    return 0;
+
+  return entry->length;
 }
 
 si_command_handler_fn si_command_get_handler(uint8_t command)
 {
-  return command_table[command].handler;
+  struct command_entry *entry = find_command(command);
+  if (entry == NULL)
+    return NULL;
+
+  return entry->handler;
 }
 
 void si_command_process()
 {
-  if (command_state == COMMAND_STATE_ERROR) {
+  if (bus_state != BUS_STATE_IDLE)
     si_await_bus_idle();
-    command_state = COMMAND_STATE_IDLE;
-  }
 
-  if (command_state == COMMAND_STATE_IDLE) {
-    command_state = COMMAND_STATE_RX;
-    si_read_command(command_buffer, on_rx_complete);
-  }
+  bus_state = BUS_STATE_BUSY;
+  si_read_command(command_buffer, on_rx_complete);
 }
 
 void si_command_processing_enable()
@@ -89,4 +132,5 @@ void si_command_processing_enable()
 void si_command_processing_disable()
 {
   auto_tx_rx_transition = false;
+  bus_state             = BUS_STATE_UNKNOWN;
 }