How can i set spis rx buffer length on nrf52832 SDK13?

[freedom118]

Hi，

i defined spis rx and tx buffer length at:

#define HUB_SPIS_RECV_BUFF_SIZE	1024
#define HUB_SPIS_SEND_BUFF_SIZE	1024

because the rx data length will be vary, so i set:

            hub_spis_recv_len=HUB_SPIS_RECV_BUFF_SIZE;
	nrf_drv_spis_buffers_set(&hub_spis,
							 hub_spis_send_buff,
							 hub_spis_send_len,
							 hub_spis_recv_buff,
							 hub_spis_recv_len);

and when i send data "Nordic thingy welcome!" from demo spi master to this spi slave, spis can't receive data from spi master, the log of spis rx bytes will be 0 in its hanlder. but when i set:

    hub_spis_recv_len=22;
err_code = nrf_drv_spis_buffers_set(&hub_spis,
									 hub_spis_send_buff,
									 hub_spis_send_len,
									 hub_spis_recv_buff,
									 hub_spis_recv_len);

spis can receive the data "Nordic thingy welcome!" from spi master.

why? and when i don't know how long data will be received on spis rx, how can i set the buffer length?

[Jørgen Holmefjord]

Hi,

The SPIS peripheral on nRF52832 use EasyDMA to store the received data directly in RAM buffer. EasyDMA have a limit on buffer size of 255 bytes, as seen from the documentation of the RXD.MAXCNT register, which is only 8 bits wide.

In the API documentation of nrf_drv_spis_buffers_set(), the type of the parameter rx_buffer_length is uint8_t, i.e., an 8-bit variable. When you assign 1024 to this variable, it will overflow and you are left with the 8 lower bits of the number (1024 dec = 0100 0000 0000 bin).

Best regards,

Jørgen

[freedom118]

Dear Jorgen，

I see. Thanks a lot. so if i want to send or receive a message longer than 255, i need to split and concat the message to packet which max length is 255.

[Jørgen Holmefjord]

Yes, that is correct.