I am looking to modify the sample code for peripheral UART and central UART, so that the central one takes data received from peripheral via BLE, and transmits said data out to some external processor via UART. External component must receive 10-byte packets with at most 1ms delay between end of one packet and start of another packet.
I am currently using 2 nRF5340-DKs to accomplish this. One of them is flashed with firmware from a direct copy of the central sample code (see nrf\samples\bluetooth\central_uart). The other has modified peripheral code (see nrf\samples\bluetooth\peripheral_uart), with the following changes:
- main.c, defined array of hardcoded data - const uint8_t data[] (with size of roughly 16,000)
- main.c, modified function ble_write_thread() to look like:
void ble_write_thread(void)
{
/* Don't go any further until BLE is initialized */
k_sem_take(&ble_init_ok, K_FOREVER);
const uint16_t len2 = 10;
uint16_t ndx = 0;
int send_err;
for (;;) {
// send 1 packet
dk_set_led(DK_LED3, 0);
if ( (send_err = bt_nus_send(NULL, data + ndx, len2)) ) {
LOG_WRN("Failed to send data over BLE connection");
printk("BLE, FAILED TO SEND (ERROR=%d)\n", send_err);
}
// prepare for next time
else {
dk_set_led(DK_LED3, 1);
if (ndx % (len2 * 100) == 0) {
printk("BLE, DATA PROGRESS (LASTBYTE=0x%02x)\n", data[ndx + len2 - 1]);
}
ndx += len2;
if (ndx >= sizeof(data)) {
printk("\n\nBLE, ALL DATA SENT; RESTARTING\n\n");
ndx = 0;
break;
}
}
// wait 1ms before sending next pkt
k_sleep(K_MSEC(1));
}
}
K_THREAD_DEFINE(ble_write_thread_id, STACKSIZE, ble_write_thread, NULL, NULL,
NULL, PRIORITY, 0, 0);
I set up a logic analyzer to read the data on the central device's UART lines, and am getting the data with no loss. But there is a 45ms delay between the end of one packet and the start of another. I noticed a similar delay on the peripheral device (used the logic analyzer on the GPIO pin for LED3, and added dk_set_led() calls to use LED's off-time to measure it).
Any ideas, thoughts, suggestions on what I can do to reduce the delay (down to at most 1ms) and speed up the BLE communication? Thanks in advance.
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Development Setup (for both peripheral and central devices):
- Board: nRF5340-DK
- Development Environment: VS Code
- SDK: nRF Connect 2.5.0
- OS: Windows 10
