diff --git a/src/spi_software.c b/src/spi_software.c
index 54b75dcd..4d5e7d97 100644
--- a/src/spi_software.c
+++ b/src/spi_software.c
@@ -4,7 +4,9 @@
 //
 // This file may be distributed under the terms of the GNU GPLv3 license.
 
+#include "autoconf.h"   // CONFIG_*
 #include "board/gpio.h" // gpio_out_setup
+#include "board/misc.h" // timer_read_time
 #include "basecmd.h" // oid_alloc
 #include "command.h" // DECL_COMMAND
 #include "sched.h" // sched_shutdown
@@ -13,6 +15,7 @@
 struct spi_software {
     struct gpio_in miso;
     struct gpio_out mosi, sclk;
+    uint32_t sck_ticks;
     uint8_t mode;
 };
 
@@ -20,6 +23,8 @@ void
 command_spi_set_software_bus(uint32_t *args)
 {
     uint8_t mode = args[4];
+    uint32_t rate = args[5];
+    uint8_t div = 0;
     if (mode > 3)
         shutdown("Invalid spi config");
 
@@ -29,6 +34,9 @@ command_spi_set_software_bus(uint32_t *args)
     ss->mosi = gpio_out_setup(args[2], 0);
     ss->sclk = gpio_out_setup(args[3], 0);
     ss->mode = mode;
+    while (((CONFIG_CLOCK_FREQ/2) >> div) > rate)
+        div++;
+    ss->sck_ticks = 1 << div;
     spidev_set_software_bus(spi, ss);
 }
 DECL_COMMAND(command_spi_set_software_bus,
@@ -41,30 +49,49 @@ spi_software_prepare(struct spi_software *ss)
     gpio_out_write(ss->sclk, ss->mode & 0x02);
 }
 
+static void
+spi_delay(uint32_t end)
+{
+    while (timer_is_before(timer_read_time(), end));
+}
+
 void
 spi_software_transfer(struct spi_software *ss, uint8_t receive_data
                       , uint8_t len, uint8_t *data)
 {
+    uint32_t t1 = ss->sck_ticks >> 1;
+    uint32_t t2 = ss->sck_ticks - t1;
+    uint32_t end = timer_read_time() + t1;
     while (len--) {
         uint8_t outbuf = *data;
         uint8_t inbuf = 0;
-        for (uint_fast8_t i = 0; i < 8; i++) {
-            if (ss->mode & 0x01) {
+        if (ss->mode & 0x01) {
+            for (uint_fast8_t i = 0; i < 8; i++) {
+                spi_delay(end);
                 // MODE 1 & 3
                 gpio_out_toggle(ss->sclk);
                 gpio_out_write(ss->mosi, outbuf & 0x80);
+                end = timer_read_time() + t2;
                 outbuf <<= 1;
-                gpio_out_toggle(ss->sclk);
                 inbuf <<= 1;
+                spi_delay(end);
+                gpio_out_toggle(ss->sclk);
                 inbuf |= gpio_in_read(ss->miso);
-            } else {
+                end = timer_read_time() + t1;
+            }
+        } else {
+            for (uint_fast8_t i = 0; i < 8; i++) {
+                spi_delay(end);
                 // MODE 0 & 2
                 gpio_out_write(ss->mosi, outbuf & 0x80);
-                outbuf <<= 1;
                 gpio_out_toggle(ss->sclk);
+                end = timer_read_time() + t2;
+                outbuf <<= 1;
                 inbuf <<= 1;
+                spi_delay(end);
                 inbuf |= gpio_in_read(ss->miso);
                 gpio_out_toggle(ss->sclk);
+                end = timer_read_time() + t1;
             }
         }