EM9287是英創(chuàng)公司新近推出的，專門針對網(wǎng)絡(luò)通訊、智能終端等應(yīng)用的工控主板產(chǎn)品。EM9287可選擇預(yù)裝Linux-3.9.7操作系統(tǒng)。在Linux-3.9.7中，AD數(shù)據(jù)采集已采用新的工業(yè)IO（簡稱IIO）驅(qū)動程序框架，本文主要介紹應(yīng)用程序如何讀取相關(guān)的AD數(shù)據(jù)。此外，英創(chuàng)公司的另一款主流工控主板產(chǎn)品EM9280也升級到Linux-3.9.7，具有與EM9287完全相同的AD通道，因此本文所介紹的AD數(shù)據(jù)讀取方法同樣適用于EM9280。

        EM9287支持2路單端模擬信號輸入AIN1和AIN2，輸入量程為 0V – 3.6V，信號管腳在CN1的17#和18#管腳。除了支持2路AD外，應(yīng)用程序還可讀取主板的CPU芯片iMX28的芯片當(dāng)前溫度，以了解設(shè)備的運(yùn)行情況。以下是測試程序：

        #include <STDIO.H>
        #include <STDLIB.H> 
        #include <FCNTL.H> 
        #include <UNISTD.H> 
        #include <MATH.H> 

        char iiotype[16][32] = { 
                ''in_voltage0_raw'', 
                'in_voltage1_raw', 
                'in_voltage2_raw', 
                'in_voltage3_raw', 
                'in_voltage4_raw', 
                'in_voltage5_raw', 
                'in_voltage6_raw', 
                'in_voltage7_raw', 
                'in_temp8_raw', 
                'in_temp9_raw', 
                'in_voltage10_raw', 
                'in_voltage11_raw', 
                'in_voltage12_raw', 
                'in_voltage13_raw', 
                'in_voltage14_raw', 
                'in_voltage15_raw' }; 

        // return = 0: voltage value from AIN1, unit: mV 
        // < 0: failed 
        int read_AIN1(float *fvoltage) 
        { 
                int value, ret = 0; 
                char filename[80]; 
                FILE *fp; 
                char buf[20]; 

                sprintf( filename, '/sys/bus/iio/devices/iio:device0/%s', iiotype[0]); 
                fp = fopen(filename, 'rt' ); 
                if( fp==NULL ) 
                { 
                        printf('open %s fail!\n', filename); 
                        *fvoltage = 0.0; 
                        ret = -1; 
                        return ret; 
                } 
                fread( buf, 1, sizeof(buf), fp ); 
                fclose(fp); 
        
                // convert to integer 
                sscanf( buf, '%d', &value ); 
                *fvoltage = 0.9 * value; 
                return ret; 
        } 

        // return = 0: voltage value from AIN2, unit: mV 
        // < 0: failed 
        int read_AIN2(float *fvoltage) 
        { 
                int value, ret = 0; 
                char filename[80]; 
                FILE *fp; 
                char buf[20]; 

                sprintf( filename, '/sys/bus/iio/devices/iio:device0/%s', iiotype[1]); 
                fp = fopen(filename, 'rt' ); 
                if( fp==NULL ) 
                { 
                        printf('open %s fail!\n', filename); 
                        *fvoltage = 0.0; 
                        ret = -1; 
                        return ret; 
                } 
                fread( buf, 1, sizeof(buf), fp ); 
                fclose(fp); 

                // convert to integer 
                sscanf( buf, '%d', &value ); 
                *fvoltage = 0.9 * value; 
                return ret; 
        } 

        // return = 0: temperature value from CPU, unit: K (Kalvin) 
        // < 0: failed 
        int read_CPU_temperature(float *ftemp) 
        { 
                int v_ch9, v_ch8, ret = 0; 
                char filename[80]; 
                FILE *fp; 
                char buf[20]; 

                sprintf( filename, '/sys/bus/iio/devices/iio:device0/%s', iiotype[9]); 
                fp = fopen(filename, 'rt' ); 
                if( fp==NULL ) 
                { 
                        printf('open %s fail!\n', filename); 
                        *ftemp = 0.0; 
                        ret = -1; 
                        return ret; 
                } 
                fread( buf, 1, sizeof(buf), fp ); 
                fclose(fp); 

                // convert to integer 
                sscanf( buf, '%d', &v_ch9 ); 

                sprintf( filename, '/sys/bus/iio/devices/iio:device0/%s', iiotype[8]); 
                fp = fopen(filename, 'rt' ); 
                if( fp==NULL ) 
                { 
                        printf('open %s fail!\n', filename); 
                        *ftemp = 0.0; 
                        ret = -1; 
                        return ret; 
                } 
                fread( buf, 1, sizeof(buf), fp ); 
                fclose(fp); 

                // convert to integer 
                sscanf( buf, '%d', &v_ch8 ); 

                *ftemp = ((float)(v_ch9 - v_ch8) * 1012) / 4000; 
                return ret; 
        } 

        int main(int argc, char** argv) 
        { 
                int ret = 0; 
                float fvalue; 

                printf('EM9280/EM9287 IIO AD test v2.0\n'); 

                // read AIN1 
                ret = read_AIN1(&fvalue); 
                if(ret < 0) 
                { 
                        return ret; 
                } 
                printf('AIN1 = %.2f mV\n', fvalue); 

                // read AIN2 
                ret = read_AIN2(&fvalue); 
                if(ret < 0) 
                { 
                        return ret; 
                } 
                printf('AIN2 = %.2f mV\n', fvalue); 

                // read CPU temperature 
                ret = read_CPU_temperature(&fvalue); 
                if(ret < 0) 
                { 
                        return ret; 
                } 
                printf('CPU Temperature = %.1f K, (%.1f C degree)\n', fvalue, (fvalue - 273)); 

                return ret; 
        }

        在控制臺（console）窗口，也可通過Linux命令查看IIO驅(qū)動的原始通道：

        進(jìn)一步，可用cat命令讀取各個(gè)通道AD轉(zhuǎn)換的原始數(shù)據(jù)，EM9280、EM9287內(nèi)部AD分辨率為12-bit，所以原始數(shù)據(jù)范圍為：0 – 4095。開發(fā)人員可通過以下命令來快速了解設(shè)備的AD數(shù)據(jù)狀況。

        #cat in_voltage0_raw //   讀取CH0的原始數(shù)據(jù)
        #cat in_voltage1_raw //   讀取CH1的原始數(shù)據(jù) 
        #cat in_temp8_raw //   讀取CPU溫度的原始數(shù)據(jù) 
        #cat in_temp9_raw //   讀取CPU溫度的原始數(shù)據(jù)

        其他的原始通道涉及EM9287的觸摸屏、內(nèi)部供電電源等，已不在本文的介紹范圍。