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lcd_st7920: Add brief delay around gpio toggle calls on fast MCUs 

On fast MCUs (like the SAMD51) it is possible for the gpio to toggle
faster than the st7920 can accept.  Add a small delay around the clock
rise signal.

Signed-off-by: Lars R. Hansen <popshansen@hotmail.com>
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2019-08-10 11:43:52 -04:00
parent a3980cebcc
commit effe6f6ddd
1 changed files with 20 additions and 0 deletions
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20
src/lcd_st7920.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_poll
@ -21,6 +22,23 @@ struct st7920 {
* 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();
}
#define SYNC_CMD 0xf8
#define SYNC_DATA 0xfa
@ -35,7 +53,9 @@ st7920_xmit_byte(struct st7920 *s, uint8_t data)
gpio_out_toggle(sid);
data = ~data;
}
ndelay(200);
gpio_out_toggle(sclk);
ndelay(200);
data <<= 1;
gpio_out_toggle(sclk);
}