From 38040fcaa3f943b26f5d5668ecea5fc4607535a7 Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Fri, 5 Sep 2025 17:21:31 -0400
Subject: debug usb

---
 fw/usb.c | 126 ++++++++++++++++++++++++++++++++++-----------------------------
 1 file changed, 69 insertions(+), 57 deletions(-)

(limited to 'fw/usb.c')

diff --git a/fw/usb.c b/fw/usb.c
index 2992888..a843945 100644
--- a/fw/usb.c
+++ b/fw/usb.c
@@ -2,6 +2,7 @@
 
 #include <stdbool.h>
 #include <stdint.h>
+#include <string.h>
 
 #include <usb.h>
 #include <usb_device.h>
@@ -20,8 +21,7 @@ enum {
 
 // State
 typedef enum {
-	IDLE, // waiting for command
-	CMD_START, // received opcode
+	IDLE,
 	ECHO,
 	WRITE_EEPROM,
 	READ_EEPROM,
@@ -29,75 +29,88 @@ typedef enum {
 
 static uint8_t readBuf[CDC_DATA_OUT_EP_SIZE];
 static uint8_t writeBuf[CDC_DATA_IN_EP_SIZE];
-static State state = IDLE;
+static uint8_t readLen = 0u;
 
 // Handle "e" echo command.
-static void
+// Returns the next state.
+static State
 echo(void) {
-	static uint8_t readLen = 0u;
-	static uint8_t ri, wi;
-
-	if (!USBUSARTIsTxTrfReady()) {
-		return;
-	}
+	uint8_t i;
+	State state = ECHO;
 
 	if (readLen == 0u) {
 		readLen = getsUSBUSART(readBuf, sizeof(readBuf));
-		ri = 0u;
-		wi = 0u;
 	}
 
-	while (readLen--) {
-		if (wi > sizeof(writeBuf)) {
-			// Overflow; flush
-			putUSBUSART(writeBuf, sizeof(writeBuf));
-			wi = 0u;
-			return; // continue on next call
-		}
-
-		writeBuf[wi] = readBuf[ri];
-		if (readBuf[ri] == '\n') {
+	for (i = 0u; i < readLen; i++) {
+		writeBuf[i] = readBuf[i];
+		if (readBuf[i] == '\n') {
 			// End of command
-			putUSBUSART(writeBuf, wi);
-			readLen = 0u;
 			state = IDLE;
-			return;
+			i++;
+			break;
 		}
+	}
 
-		ri++;
-		wi++;
+	if (readLen > 0u) {
+		putUSBUSART(writeBuf, i);
 	}
+	readLen = 0u;
+
+	return state;
 }
 
 // Handle "w" write eeprom command.
-static void
+// Returns the next state.
+static State
 writeEeprom(void) {
 	// TODO
+	return IDLE;
 }
 
 // Handle "r" read eeprom command.
-static void readEeprom(void) {
+// Returns the next state.
+static State
+readEeprom(void) {
 	// TODO
+	return IDLE;
 }
 
-static void
-setCmdState(uint8_t opcode) {
+static State
+cmdState(uint8_t opcode) {
 	switch (opcode) {
-	case 'e': // echo
-		state = ECHO;
-		break;
-	case 'w':
-		state = WRITE_EEPROM;
-		break;
-	case 'r':
-		state = READ_EEPROM;
-		break;
+	case 'e': return ECHO;
+	case 'w': return WRITE_EEPROM;
+	case 'r': return READ_EEPROM;
+	default: return IDLE; // invalid command
 	}
 }
 
+// Read (the start of) a command from USB.
+// Leaves <args> at the beginning of the read buffer.
+// Returns the next state based on the opcode of the command.
+static State
+readCmd(void) {
+	uint8_t opcode;
+
+	readLen = getsUSBUSART(readBuf, sizeof(readBuf));
+	if (readLen < 2u) {
+		// Invalid command. Must start with <opcode> <space>
+		return IDLE;
+	}
+
+	opcode = readBuf[0u];
+
+	// skip <opcode> <space>
+	memmove(readBuf, readBuf+2u, readLen-2u);
+	readLen -= 2u;
+
+	return cmdState(opcode);
+}
+
 void
 usbTask(void) {
-	static uint8_t opcode = 0u;
+	static State state = IDLE;
 
 	USBDeviceTasks();
 
@@ -108,23 +121,13 @@ usbTask(void) {
 		return;
 	}
 
-	switch (state) {
-	case IDLE:
-		if (getsUSBUSART(&opcode, 1u) > 0) {
-			state = CMD_START;
-		}
-		break;
-	case CMD_START:
-		// Skip space char
-		if (getsUSBUSART(readBuf, 1u) > 0) {
-			setCmdState(opcode);
+	if (USBUSARTIsTxTrfReady()) {
+		switch (state) {
+		case IDLE: state = readCmd(); break;
+		case ECHO: state = echo(); break;
+		case WRITE_EEPROM: state = writeEeprom(); break;
+		case READ_EEPROM: state = readEeprom(); break;
 		}
-	case ECHO: echo();
-		break;
-	case WRITE_EEPROM: writeEeprom();
-		break;
-	case READ_EEPROM: readEeprom();
-		break;
 	}
 
 	CDCTxService();
@@ -143,25 +146,34 @@ USER_USB_CALLBACK_EVENT_HANDLER(USB_EVENT event, void *pdata, uint16_t size) {
 	switch ((int)event) {
 	case EVENT_TRANSFER:
 		break;
+
 	case EVENT_SOF:
 		break;
+
 	case EVENT_SUSPEND:
 		break;
+
 	case EVENT_RESUME:
 		break;
+
 	case EVENT_CONFIGURED:
 		CDCInitEP();
 		configure();
 		break;
+
 	case EVENT_SET_DESCRIPTOR:
 		break;
+
 	case EVENT_EP0_REQUEST:
 		USBCheckCDCRequest();
 		break;
+
 	case EVENT_BUS_ERROR:
 		break;
+
 	case EVENT_TRANSFER_TERMINATED:
 		break;
+
 	default:
 		break;
 	}
-- 
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