From ba6fb7522c7333b3a9081a823f2b93a425b36022 Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Thu, 4 Sep 2025 19:05:46 -0400
Subject: fw: usb

---
 fw/usb.c | 170 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 170 insertions(+)
 create mode 100644 fw/usb.c

(limited to 'fw/usb.c')

diff --git a/fw/usb.c b/fw/usb.c
new file mode 100644
index 0000000..2992888
--- /dev/null
+++ b/fw/usb.c
@@ -0,0 +1,170 @@
+#include <xc.h>
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#include <usb.h>
+#include <usb_device.h>
+#include <usb_device_cdc.h>
+
+#include "usb.h"
+
+// Line coding
+// See struct USB_CDC_LINE_CODING
+enum {
+	DATA_RATE = 9600, // bps
+	CHAR_FORMAT = NUM_STOP_BITS_1,
+	PARITY_TYPE = PARITY_NONE,
+	DATA_BITS = 8,
+};
+
+// State
+typedef enum {
+	IDLE, // waiting for command
+	CMD_START, // received opcode
+	ECHO,
+	WRITE_EEPROM,
+	READ_EEPROM,
+} State;
+
+static uint8_t readBuf[CDC_DATA_OUT_EP_SIZE];
+static uint8_t writeBuf[CDC_DATA_IN_EP_SIZE];
+static State state = IDLE;
+
+// Handle "e" echo command.
+static void
+echo(void) {
+	static uint8_t readLen = 0u;
+	static uint8_t ri, wi;
+
+	if (!USBUSARTIsTxTrfReady()) {
+		return;
+	}
+
+	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') {
+			// End of command
+			putUSBUSART(writeBuf, wi);
+			readLen = 0u;
+			state = IDLE;
+			return;
+		}
+
+		ri++;
+		wi++;
+	}
+}
+
+// Handle "w" write eeprom command.
+static void
+writeEeprom(void) {
+	// TODO
+}
+
+// Handle "r" read eeprom command.
+static void readEeprom(void) {
+	// TODO
+}
+
+static void
+setCmdState(uint8_t opcode) {
+	switch (opcode) {
+	case 'e': // echo
+		state = ECHO;
+		break;
+	case 'w':
+		state = WRITE_EEPROM;
+		break;
+	case 'r':
+		state = READ_EEPROM;
+		break;
+	}
+}
+
+void
+usbTask(void) {
+	static uint8_t opcode = 0u;
+
+	USBDeviceTasks();
+
+	if (USBGetDeviceState() < CONFIGURED_STATE) {
+		return;
+	}
+	if (USBIsDeviceSuspended()) {
+		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);
+		}
+	case ECHO: echo();
+		break;
+	case WRITE_EEPROM: writeEeprom();
+		break;
+	case READ_EEPROM: readEeprom();
+		break;
+	}
+
+	CDCTxService();
+}
+
+static void
+configure(void) {
+	line_coding.dwDTERate = DATA_RATE;
+	line_coding.bCharFormat = CHAR_FORMAT;
+	line_coding.bParityType = PARITY_TYPE;
+	line_coding.bDataBits = DATA_BITS;
+}
+
+bool
+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;
+	}
+
+	return true;
+}
-- 
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