From dfc09d8b14d15015b4afa5d674786ec74f616772 Mon Sep 17 00:00:00 2001
From: lonkaars <loek@pipeframe.xyz>
Date: Sun, 12 May 2024 15:00:54 +0200
Subject: get pin 19 working

---
 1/config.h | 15 +++++++++++++--
 1/fopdrv.c | 11 ++++++++++-
 1/main.c   | 21 +++++++++++++++++++++
 readme.md  |  4 ++++
 4 files changed, 48 insertions(+), 3 deletions(-)

diff --git a/1/config.h b/1/config.h
index 6326354..dbe3a86 100644
--- a/1/config.h
+++ b/1/config.h
@@ -9,7 +9,18 @@
 typedef uint32_t ti_am335x_word_t;
 
 // p. 180: "Control Module"
-#define TI_AM335X_CM_ADDR ((ti_am335x_word_t*) 0x44E1_0000)
+#define TI_AM335X_CM_ADDR 0x44E10000
+// p. 182: "GPIO1"
+#define TI_AM335X_GPIO1_ADDR 0x4804C000
 // p. 1459: "conf_gpmc_a3"
-#define TI_AM335X_CM_GPMC_A3_ADDR ((ti_am335x_word_t*) TI_AM3358_CM_ADDR + 0x84Ch)
+#define TI_AM335X_CM_GPMC_A3_ADDR (TI_AM335X_CM_ADDR + 0x84C)
 
+// p. 4990, variable names copied as-is
+#define GPIO_OE (0x134 / (sizeof(ti_am335x_word_t)))
+#define GPIO_DATAIN (0x138 / (sizeof(ti_am335x_word_t)))
+#define GPIO_CLEARDATAOUT (0x190 / (sizeof(ti_am335x_word_t)))
+#define GPIO_SETDATAOUT (0x194 / (sizeof(ti_am335x_word_t)))
+// total size of GPIO registers from p. 4990 (in bytes)
+#define GPIO_REG_SIZE 0x198
+
+#define PIN 19
diff --git a/1/fopdrv.c b/1/fopdrv.c
index e0ad41c..d048f15 100644
--- a/1/fopdrv.c
+++ b/1/fopdrv.c
@@ -1,4 +1,7 @@
+#include <linux/io.h>
+
 #include "fopdrv.h"
+#include "config.h"
 
 // driver/char/mem.c read_null (/dev/null)
 ssize_t fop_read(struct file *file, char __user *buf, size_t count, loff_t *ppos) {
@@ -6,7 +9,6 @@ ssize_t fop_read(struct file *file, char __user *buf, size_t count, loff_t *ppos
 	return 0;
 }
 
-// driver/char/mem.c write_null
 ssize_t fop_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos) {
 	printk("%s(<file>, <buf>, %u, <ppos>)\n", __PRETTY_FUNCTION__, count);
 
@@ -18,13 +20,20 @@ ssize_t fop_write(struct file *file, const char __user *buf, size_t count, loff_
 	if (copy_from_user(input_buf + *ppos, buf, count))
 		return -EFAULT;
 
+	ti_am335x_word_t* gpio1 = ioremap(TI_AM335X_GPIO1_ADDR, GPIO_REG_SIZE);
+	barrier();
+
 	if (input_buf[0] == '0') {
 		printk("TODO: TURN OFF OUTPUT\n");
+		iowrite32((1<<PIN), gpio1 + GPIO_CLEARDATAOUT); wmb();
 	}
 	if (input_buf[0] == '1') {
 		printk("TODO: TURN ON OUTPUT\n");
+		iowrite32((1<<PIN), gpio1 + GPIO_SETDATAOUT); wmb();
 	}
 
+	iounmap(gpio1);
+
 	return count;
 }
 
diff --git a/1/main.c b/1/main.c
index 5410df7..d8ea7fc 100644
--- a/1/main.c
+++ b/1/main.c
@@ -1,6 +1,7 @@
 #include <linux/cdev.h>
 #include <linux/init.h>
 #include <linux/module.h>
+#include <linux/io.h>
 
 #include "fopdrv.h"
 #include "config.h"
@@ -63,6 +64,26 @@ static int mod_init(void) {
 
 	printk("%s() -> 0 (%d:%d)\n", __PRETTY_FUNCTION__, MAJOR(node), MINOR(node));
 	printk("one = %d, two = %d\n", one, not_named_two);
+
+	// configure gpio mux
+	uint32_t* conf_gpmc_a3 = ioremap(TI_AM335X_CM_GPMC_A3_ADDR, sizeof(ti_am335x_word_t));
+	if (conf_gpmc_a3 == NULL)
+		return -EINVAL;
+	barrier();
+	uint32_t val = ioread32(conf_gpmc_a3); rmb();
+	val &= ~0x7;
+	val |= 0x7;
+	iowrite32(val, conf_gpmc_a3); wmb();
+	iounmap(conf_gpmc_a3);
+
+	// configure output pin
+	ti_am335x_word_t* gpio1 = ioremap(TI_AM335X_GPIO1_ADDR, GPIO_REG_SIZE);
+	barrier();
+	ti_am335x_word_t oe_reg = ioread32(gpio1 + GPIO_OE); rmb();
+	oe_reg &= ~(1<<PIN); // 0=output
+	iowrite32(oe_reg, gpio1 + GPIO_OE); wmb();
+	iounmap(gpio1);
+
 	return 0;
 
 free_device:
diff --git a/readme.md b/readme.md
index ef2f63a..a03a3d3 100644
--- a/readme.md
+++ b/readme.md
@@ -13,6 +13,8 @@
 - [Linux kernel labs - character device drivers][kernel-labs-chrdev]
 - [Core API][core-api]
 - [Driver API][driver-api]
+- [AM335x Technical reference manual][ti-am335x-rm]
+- [BeagleBone Black system reference manual][bbb-srm]
 
 [kbuild-obj-var]: https://docs.kernel.org/kbuild/makefiles.html#loadable-module-goals-obj-m
 [kbuild-module-makefile]: https://www.kernel.org/doc/html/latest/kbuild/modules.html#creating-a-kbuild-file-for-an-external-module
@@ -21,6 +23,8 @@
 [kernel-labs-chrdev]: https://linux-kernel-labs.github.io/refs/heads/master/labs/device_drivers.html
 [core-api]: https://docs.kernel.org/core-api/kernel-api.html
 [driver-api]: https://www.kernel.org/doc/html/latest/driver-api/infrastructure.html
+[ti-am335x-rm]: https://www.ti.com/lit/ug/spruh73q/spruh73q.pdf
+[bbb-srm]: https://cdn-shop.adafruit.com/datasheets/BBB_SRM.pdf
 
 # tips
 
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