lcd_hd44780: Add proper timing delays around gpio updates

A fast micro-controller may update the gpio pins faster than the
hd44780 chip can handle.  Add in the appropriate delays.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

1 files changed, 20 insertions, 0 deletions

diff --git a/src/lcd_hd44780.c b/src/lcd_hd44780.c
index 9c23814b..fe65f5cf 100644
--- a/src/lcd_hd44780.c
+++ b/src/lcd_hd44780.c
@@ -4,6 +4,7 @@
 //
 // This file may be distributed under the terms of the GNU GPLv3 license.
 
+#include "autoconf.h" // CONFIG_CLOCK_FREQ
 #include "basecmd.h" // oid_alloc
 #include "board/gpio.h" // gpio_out_write
 #include "board/irq.h" // irq_disable
@@ -22,6 +23,23 @@ struct hd44780 {
  * Transmit functions
  ****************************************************************/
 
+static uint32_t
+nsecs_to_ticks(uint32_t ns)
+{
+    return timer_from_us(ns * 1000) / 1000000;
+}
+
+static inline void
+ndelay(uint32_t nsecs)
+{
+    if (CONFIG_CLOCK_FREQ <= 48000000)
+        // Slower MCUs don't require a delay
+        return;
+    uint32_t end = timer_read_time() + nsecs_to_ticks(nsecs);
+    while (timer_is_before(timer_read_time(), end))
+        irq_poll();
+}
+
 // Write 4 bits to the hd44780 using the 4bit parallel interface
 static __always_inline void
 hd44780_xmit_bits(uint8_t toggle, struct gpio_out e, struct gpio_out d4
@@ -36,6 +54,7 @@ hd44780_xmit_bits(uint8_t toggle, struct gpio_out e, struct gpio_out d4
         gpio_out_toggle(d6);
     if (toggle & 0x80)
         gpio_out_toggle(d7);
+    ndelay(80);
     gpio_out_toggle(e);
 }
 
@@ -46,6 +65,7 @@ hd44780_xmit_byte(struct hd44780 *h, uint8_t data)
     struct gpio_out e = h->e, d4 = h->d4, d5 = h->d5, d6 = h->d6, d7 = h->d7;
     hd44780_xmit_bits(h->last ^ data, e, d4, d5, d6, d7);
     h->last = data << 4;
+    ndelay(500 - 80);
     hd44780_xmit_bits(data ^ h->last, e, d4, d5, d6, d7);
 }