HID output report size and count

Question

Hello, 
 I am developing a simple HID device with output report to receive data from PC. I took keyboard example as base project and I want to increase output report size (count) up to 64 bytes. 
 I can successfully send data from PC to device when output report is not larger than 1 byte. If I change size or count in descriptor, data transmission is not working. 
 I use c# code to connect to device and send byte buffer. It does not show any errors, I have just "success" or "fail". 
 Device is recognized by the PC correctly. 
 Here is my descriptor 
 #define HID_CONTROL_REPORT_DESCRIPTOR() { \
 0x05, 0x01, /* USAGE_PAGE (Generic Desktop)*/	\
 0x09, 0x00, /* USAGE (Undefined)*/	\
 0xa1, 0x01, /* COLLECTION (Application)*/	\
 0x75, 0x08, /* REPORT_SIZE (1)*/	\
 0x95, 0x01, /* REPORT_COUNT (1)*/	\
 0x15, 0x00, /* LOGICAL_MINIMUM (0)*/	\
 0x25, 0x7F, /* LOGICAL_MAXIMUM (127)*/	\
 0x09, 0x01, /* USAGE (Consumer Control)*/	\
 0x91, 0x02, /* OUTPUT (Data,Ary,Abs)*/	\
 0xc0 /* END_COLLECTION*/	\
} 
 It works perfectly. But if I increase REPORT_COUNT, or REPORT_SIZE, it stops receiving data from PC

ilia · Accepted Answer

Ok, I found what causes such behavior. 
 Apparently, changing REPORT_COUNT in HID descriptor is not enough. For example, there is a app_usbd_hid_kbd_internal.h file for keyboard descriptor. In this file there is global definition of app_usbd_hid_kbd_t class: 
 #define APP_USBD_HID_KBD_GLOBAL_DEF_INTERNAL(instance_name, \
 interface_number, \
 endpoint, \
 user_ev_handler, \
 subclass_boot) \
 static app_usbd_hid_report_buffer_t CONCAT_2(instance_name, _in)[1]; \
 static uint8_t CONCAT_2(instance_name, _ep) = {MACRO_MAP(APP_USBD_HID_KBD_INTERVAL,endpoint)}; \
 APP_USBD_HID_GENERIC_GLOBAL_OUT_REP_DEF(CONCAT_2(instance_name, _out), 1 + 1); \
 APP_USBD_CLASS_INST_GLOBAL_DEF( \
 instance_name, \
 app_usbd_hid_kbd, \
 &app_usbd_hid_kbd_class_methods, \
 APP_USBD_HID_KBD_CONFIG(interface_number, endpoint), \
 (APP_USBD_HID_KBD_INST_CONFIG(CONCAT_2(instance_name, _in), \
 &CONCAT_2(instance_name, _out), \
 user_ev_handler, \
 subclass_boot, \
 &CONCAT_2(instance_name, _ep))) \
 ) 
 The following line looks like definition of the output report: 
 APP_USBD_HID_GENERIC_GLOBAL_OUT_REP_DEF(CONCAT_2(instance_name, _out), 1 + 1); 
 That "1 + 1" looks like size of this output report: 1 byte for Report_ID + 1 byte for data that was defined in descriptor. 
 Thus, when I change Report_Count in descriptor, I can't receive more data because I specified here only 2 byte buffer. And I also can't receive same 1 byte data because my descriptor requires larger byte count. 
 So, in the global definition for my custom hid class I changed that "1 + 1" to "1 + 64" and updated my descriptor with 64 bytes output report count. And it works.

HID output report size and count

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