nodemcu-firmware: Hardware timer (platform_hw_timer_*) causing freeze

I am building a module to radio control Somfy blinds via 433Mhz RF transmitter. A sequence of 0 and 1 with different delays needs to be transmitted as illustrated on the chart:

There are implementations for Arduino using delay functions but on ESP8266 I need to go asynchronous. That is why I have decided to use the hw_timer to achieve precise timing in the order of microseconds.

Actual behavior

I am indeed able to control blinds but after sending few commands the ESP8266 freezes and then goes restart triggered by hw watchdog (rst cause: 4, boot mode:(3,0)).

Test code

The minimum code to reproduce the issue is

modules\somfy.c

#include "os_type.h"
#include "osapi.h"

#include "module.h"
#include "lauxlib.h"
#include "platform.h"
#include "hw_timer.h"
#include "user_interface.h"

#define SYMBOL 640 // symbol width in microseconds

#define TIMER_OWNER ((os_param_t) 's')

static uint32_t   delay[10] = {9415, 89565, 4*SYMBOL, 4*SYMBOL, 4*SYMBOL, 4550, SYMBOL, SYMBOL, SYMBOL, 30415}; // 143 ms total
static uint8_t    signalindex;

static void ICACHE_RAM_ATTR sendCommand(os_param_t p) {
    (void) p;
    //NODE_DBG("%d\n", signalindex);
    signalindex++;
    if (signalindex<10) {
        platform_hw_timer_arm_us(TIMER_OWNER, delay[signalindex-1]);
    } else {
        platform_hw_timer_close(TIMER_OWNER);
    }
}

static int somfy_lua_sendcommand(lua_State* L) {
    if (!platform_hw_timer_init(TIMER_OWNER, NMI_SOURCE, TRUE)) {
        // Failed to init the timer
        luaL_error(L, "Unable to initialize timer");
    }
    NODE_DBG("Triggering hw timer (%d)\n",  system_get_time());
    platform_hw_timer_set_func(TIMER_OWNER, sendCommand, 0);
    signalindex=0;
    sendCommand(0);
    return 0;
}

static const LUA_REG_TYPE somfy_map[] = {
    { LSTRKEY( "sendcommand" ), LFUNCVAL(somfy_lua_sendcommand)},
    { LNILKEY, LNILVAL}
};

NODEMCU_MODULE(SOMFY, "somfy", somfy_map, NULL);

and the Lua code to trigger it

tmr.alarm(0, 250, tmr.ALARM_AUTO, function() somfy.sendcommand() end)

The Lua code freezes and crashes in less than 1 minute. The sendcommand calls platform_hw_timer_close() in less than 150ms so there should be no issue that the function is called when the timer is still running.

Am I doing something which is not compliant with specifications?

NodeMCU version

I am using dev branch, version up to 56b4a3e commit. Modules included: file, gpio, net, node, tmr, uart, wifi.

Hardware

ESP-01. No need to connect the RF transmitter to reproduce the issue.