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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>
This commit is contained in:
Kevin O'Connor 2019-11-26 09:34:42 -05:00
parent 35de9b8e55
commit fb485e862d
1 changed files with 20 additions and 0 deletions
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20
src/lcd_hd44780.c
View File

@ -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);
}